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.TH LIBPNG 3 "December 3, 2004"
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.SH NAME
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libpng \- Portable Network Graphics (PNG) Reference Library 1.2.8
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.SH SYNOPSIS
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\fI\fB
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\fB#include <png.h>\fP
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\fI\fB
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\fBpng_uint_32 png_access_version_number \fI(void\fP\fB);\fP
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\fI\fB
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\fBint png_check_sig (png_bytep \fP\fIsig\fP\fB, int \fInum\fP\fB);\fP
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\fI\fB
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\fBvoid png_chunk_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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\fI\fB
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\fBvoid png_chunk_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
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\fI\fB
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\fBvoid png_convert_from_struct_tm (png_timep \fP\fIptime\fP\fB, struct tm FAR * \fIttime\fP\fB);\fP
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\fI\fB
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\fBvoid png_convert_from_time_t (png_timep \fP\fIptime\fP\fB, time_t \fIttime\fP\fB);\fP
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\fI\fB
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\fBpng_charp png_convert_to_rfc1123 (png_structp \fP\fIpng_ptr\fP\fB, png_timep \fIptime\fP\fB);\fP
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\fI\fB
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\fBpng_infop png_create_info_struct (png_structp \fIpng_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_structp png_create_read_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
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\fI\fB
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\fBpng_structp png_create_read_struct_2(png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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\fI\fB
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\fBpng_structp png_create_write_struct (png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarn_fn\fP\fB);\fP
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\fI\fB
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\fBpng_structp png_create_write_struct_2(png_const_charp \fP\fIuser_png_ver\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fP\fIwarn_fn\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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\fI\fB
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\fBint png_debug(int \fP\fIlevel\fP\fB, png_const_charp \fImessage\fP\fB);\fP
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\fI\fB
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\fBint png_debug1(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fIp1\fP\fB);\fP
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\fI\fB
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\fBint png_debug2(int \fP\fIlevel\fP\fB, png_const_charp \fP\fImessage\fP\fB, \fP\fIp1\fP\fB, \fIp2\fP\fB);\fP
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\fI\fB
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\fBvoid png_destroy_info_struct (png_structp \fP\fIpng_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
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\fI\fB
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\fBvoid png_destroy_read_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fP\fIinfo_ptr_ptr\fP\fB, png_infopp \fIend_info_ptr_ptr\fP\fB);\fP
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\fI\fB
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\fBvoid png_destroy_write_struct (png_structpp \fP\fIpng_ptr_ptr\fP\fB, png_infopp \fIinfo_ptr_ptr\fP\fB);\fP
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\fI\fB
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\fBvoid png_error (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fIerror\fP\fB);\fP
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\fI\fB
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\fBvoid png_free (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
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\fI\fB
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\fBvoid png_free_chunk_list (png_structp \fIpng_ptr\fP\fB);\fP
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\fI\fB
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\fBvoid png_free_default(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fIptr\fP\fB);\fP
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\fI\fB
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\fBvoid png_free_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fInum\fP\fB);\fP
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\fI\fB
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\fBpng_byte png_get_bit_depth (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fI*background\fP\fB);\fP
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\fI\fB
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\fBpng_byte png_get_channels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fI*white_x\fP\fB, double \fP\fI*white_y\fP\fB, double \fP\fI*red_x\fP\fB, double \fP\fI*red_y\fP\fB, double \fP\fI*green_x\fP\fB, double \fP\fI*green_y\fP\fB, double \fP\fI*blue_x\fP\fB, double \fI*blue_y\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*white_x\fP\fB, png_uint_32 \fP\fI*white_y\fP\fB, png_uint_32 \fP\fI*red_x\fP\fB, png_uint_32 \fP\fI*red_y\fP\fB, png_uint_32 \fP\fI*green_x\fP\fB, png_uint_32 \fP\fI*green_y\fP\fB, png_uint_32 \fP\fI*blue_x\fP\fB, png_uint_32 \fI*blue_y\fP\fB);\fP
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\fI\fB
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\fBpng_byte png_get_color_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_byte png_get_compression_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_byte png_get_copyright (png_structp \fIpng_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_voidp png_get_error_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_byte png_get_filter_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fI*file_gamma\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fI*int_file_gamma\fP\fB);\fP
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\fI\fB
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\fBpng_byte png_get_header_ver (png_structp \fIpng_ptr\fP\fB);\fP
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\fBpng_byte png_get_header_version (png_structp \fIpng_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fI*hist\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charpp \fP\fIname\fP\fB, int \fP\fI*compression_type\fP\fB, png_charpp \fP\fIprofile\fP\fB, png_uint_32 \fI*proflen\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*width\fP\fB, png_uint_32 \fP\fI*height\fP\fB, int \fP\fI*bit_depth\fP\fB, int \fP\fI*color_type\fP\fB, int \fP\fI*interlace_type\fP\fB, int \fP\fI*compression_type\fP\fB, int \fI*filter_type\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_image_height (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_image_width (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_byte png_get_interlace_type (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_voidp png_get_io_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_byte png_get_libpng_ver (png_structp \fIpng_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_voidp png_get_mem_ptr(png_structp \fIpng_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*offset_x\fP\fB, png_uint_32 \fP\fI*offset_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fI*purpose\fP\fB, png_int_32 \fP\fI*X0\fP\fB, png_int_32 \fP\fI*X1\fP\fB, int \fP\fI*type\fP\fB, int \fP\fI*nparams\fP\fB, png_charp \fP\fI*units\fP\fB, png_charpp \fI*params\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fI*res_x\fP\fB, png_uint_32 \fP\fI*res_y\fP\fB, int \fI*unit_type\fP\fB);\fP
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\fI\fB
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\fBfloat png_get_pixel_aspect_ratio (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_voidp png_get_progressive_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fI*palette\fP\fB, int \fI*num_palette\fP\fB);\fP
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\fI\fB
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\fBpng_byte png_get_rgb_to_gray_status (png_structp \fIpng_ptr)
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\fBpng_uint_32 png_get_rowbytes (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_bytepp png_get_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fI*sig_bit\fP\fB);\fP
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\fI\fB
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\fBpng_bytep png_get_signature (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fI*splt_ptr\fP\fB);\fP
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\fI\fB
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\fBpng_uint_32 png_get_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fI*intent\fP\fB);\fP
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\fI\fB
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249 |
\fBpng_uint_32 png_get_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fI*text_ptr\fP\fB, int \fI*num_text\fP\fB);\fP
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250 |
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251 |
\fI\fB
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252 |
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253 |
\fBpng_uint_32 png_get_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fI*mod_time\fP\fB);\fP
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254 |
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255 |
\fI\fB
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256 |
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257 |
\fBpng_uint_32 png_get_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fI*trans\fP\fB, int \fP\fI*num_trans\fP\fB, png_color_16p \fI*trans_values\fP\fB);\fP
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258 |
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259 |
\fI\fB
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260 |
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261 |
\fBpng_uint_32 png_get_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkpp \fIunknowns\fP\fB);\fP
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262 |
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263 |
\fI\fB
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264 |
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265 |
\fBpng_voidp png_get_user_chunk_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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266 |
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267 |
\fI\fB
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268 |
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269 |
\fBpng_uint_32 png_get_user_height_max( png_structp \fIpng_ptr\fP\fB);\fP
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270 |
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271 |
\fI\fB
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272 |
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273 |
\fBpng_voidp png_get_user_transform_ptr (png_structp \fIpng_ptr\fP\fB);\fP
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274 |
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275 |
\fI\fB
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276 |
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277 |
\fBpng_uint_32 png_get_user_width_max (png_structp \fIpng_ptr\fP\fB);\fP
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278 |
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279 |
\fI\fB
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280 |
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281 |
\fBpng_uint_32 png_get_valid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIflag\fP\fB);\fP
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282 |
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283 |
\fI\fB
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284 |
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285 |
\fBpng_int_32 png_get_x_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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286 |
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287 |
\fI\fB
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288 |
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289 |
\fBpng_int_32 png_get_x_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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290 |
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291 |
\fI\fB
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292 |
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293 |
\fBpng_uint_32 png_get_x_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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294 |
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295 |
\fI\fB
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296 |
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297 |
\fBpng_int_32 png_get_y_offset_microns (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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298 |
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299 |
\fI\fB
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300 |
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301 |
\fBpng_int_32 png_get_y_offset_pixels (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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302 |
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\fI\fB
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304 |
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\fBpng_uint_32 png_get_y_pixels_per_meter (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
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306 |
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307 |
\fI\fB
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308 |
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309 |
\fBpng_uint_32 png_get_compression_buffer_size (png_structp \fIpng_ptr\fP\fB);\fP
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310 |
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311 |
\fI\fB
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312 |
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313 |
\fBint png_handle_as_unknown (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIchunk_name\fP\fB);\fP
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314 |
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315 |
\fI\fB
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316 |
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317 |
\fBvoid png_init_io (png_structp \fP\fIpng_ptr\fP\fB, FILE \fI*fp\fP\fB);\fP
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318 |
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319 |
\fI\fB
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320 |
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321 |
\fBDEPRECATED: void png_info_init (png_infop \fIinfo_ptr\fP\fB);\fP
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\fI\fB
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324 |
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325 |
\fBDEPRECATED: void png_info_init_2 (png_infopp \fP\fIptr_ptr\fP\fB, png_size_t \fIpng_info_struct_size\fP\fB);\fP
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326 |
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327 |
\fI\fB
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328 |
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329 |
\fBpng_voidp png_malloc (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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330 |
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331 |
\fI\fB
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332 |
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333 |
\fBpng_voidp png_malloc_default(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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334 |
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335 |
\fI\fB
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336 |
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337 |
\fBvoidp png_memcpy (png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_size_t \fIsize\fP\fB);\fP
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338 |
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339 |
\fI\fB
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340 |
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341 |
\fBpng_voidp png_memcpy_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, png_voidp \fP\fIs2\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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342 |
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343 |
\fI\fB
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344 |
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345 |
\fBvoidp png_memset (png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_size_t \fIsize\fP\fB);\fP
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346 |
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347 |
\fI\fB
|
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348 |
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349 |
\fBpng_voidp png_memset_check (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIs1\fP\fB, int \fP\fIvalue\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
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350 |
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|
351 |
\fI\fB
|
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352 |
|
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353 |
\fBDEPRECATED: void png_permit_empty_plte (png_structp \fP\fIpng_ptr\fP\fB, int \fIempty_plte_permitted\fP\fB);\fP
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354 |
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355 |
\fI\fB
|
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356 |
|
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357 |
\fBvoid png_process_data (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fIbuffer\fP\fB, png_size_t \fIbuffer_size\fP\fB);\fP
|
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358 |
|
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|
359 |
\fI\fB
|
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|
360 |
|
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|
361 |
\fBvoid png_progressive_combine_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIold_row\fP\fB, png_bytep \fInew_row\fP\fB);\fP
|
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362 |
|
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|
363 |
\fI\fB
|
|
|
364 |
|
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|
365 |
\fBvoid png_read_destroy (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_infop \fIend_info_ptr\fP\fB);\fP
|
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|
366 |
|
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|
367 |
\fI\fB
|
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|
368 |
|
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|
369 |
\fBvoid png_read_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
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|
370 |
|
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|
371 |
\fI\fB
|
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|
372 |
|
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|
373 |
\fBvoid png_read_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
|
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|
374 |
|
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|
375 |
\fI\fB
|
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|
376 |
|
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|
377 |
\fBDEPRECATED: void png_read_init (png_structp \fIpng_ptr\fP\fB);\fP
|
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|
378 |
|
|
|
379 |
\fI\fB
|
|
|
380 |
|
|
|
381 |
\fBDEPRECATED: void png_read_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
|
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|
382 |
|
|
|
383 |
\fI\fB
|
|
|
384 |
|
|
|
385 |
\fBvoid png_read_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|
|
386 |
|
|
|
387 |
\fI\fB
|
|
|
388 |
|
|
|
389 |
\fBvoid png_read_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
|
|
|
390 |
|
|
|
391 |
\fI\fB
|
|
|
392 |
|
|
|
393 |
\fBvoid png_read_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIrow\fP\fB, png_bytep \fIdisplay_row\fP\fB);\fP
|
|
|
394 |
|
|
|
395 |
\fI\fB
|
|
|
396 |
|
|
|
397 |
\fBvoid png_read_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_bytepp \fP\fIdisplay_row\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
|
|
|
398 |
|
|
|
399 |
\fI\fB
|
|
|
400 |
|
|
|
401 |
\fBvoid png_read_update_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|
|
402 |
|
|
|
403 |
\fI\fB
|
|
|
404 |
|
|
|
405 |
\fB#if \fI!defined(PNG_1_0_X)
|
|
|
406 |
|
|
|
407 |
\fBvoid png_set_add_alpha (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
|
|
|
408 |
|
|
|
409 |
\fI\fB#endif
|
|
|
410 |
|
|
|
411 |
\fI\fB
|
|
|
412 |
|
|
|
413 |
\fBvoid png_set_background (png_structp \fP\fIpng_ptr\fP\fB, png_color_16p \fP\fIbackground_color\fP\fB, int \fP\fIbackground_gamma_code\fP\fB, int \fP\fIneed_expand\fP\fB, double \fIbackground_gamma\fP\fB);\fP
|
|
|
414 |
|
|
|
415 |
\fI\fB
|
|
|
416 |
|
|
|
417 |
\fBvoid png_set_bgr (png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
418 |
|
|
|
419 |
\fI\fB
|
|
|
420 |
|
|
|
421 |
\fBvoid png_set_bKGD (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_16p \fIbackground\fP\fB);\fP
|
|
|
422 |
|
|
|
423 |
\fI\fB
|
|
|
424 |
|
|
|
425 |
\fBvoid png_set_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fP\fIwhite_x\fP\fB, double \fP\fIwhite_y\fP\fB, double \fP\fIred_x\fP\fB, double \fP\fIred_y\fP\fB, double \fP\fIgreen_x\fP\fB, double \fP\fIgreen_y\fP\fB, double \fP\fIblue_x\fP\fB, double \fIblue_y\fP\fB);\fP
|
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|
426 |
|
|
|
427 |
\fI\fB
|
|
|
428 |
|
|
|
429 |
\fBvoid png_set_cHRM_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwhite_x\fP\fB, png_uint_32 \fP\fIwhite_y\fP\fB, png_uint_32 \fP\fIred_x\fP\fB, png_uint_32 \fP\fIred_y\fP\fB, png_uint_32 \fP\fIgreen_x\fP\fB, png_uint_32 \fP\fIgreen_y\fP\fB, png_uint_32 \fP\fIblue_x\fP\fB, png_uint_32 \fIblue_y\fP\fB);\fP
|
|
|
430 |
|
|
|
431 |
\fI\fB
|
|
|
432 |
|
|
|
433 |
\fBvoid png_set_compression_level (png_structp \fP\fIpng_ptr\fP\fB, int \fIlevel\fP\fB);\fP
|
|
|
434 |
|
|
|
435 |
\fI\fB
|
|
|
436 |
|
|
|
437 |
\fBvoid png_set_compression_mem_level (png_structp \fP\fIpng_ptr\fP\fB, int \fImem_level\fP\fB);\fP
|
|
|
438 |
|
|
|
439 |
\fI\fB
|
|
|
440 |
|
|
|
441 |
\fBvoid png_set_compression_method (png_structp \fP\fIpng_ptr\fP\fB, int \fImethod\fP\fB);\fP
|
|
|
442 |
|
|
|
443 |
\fI\fB
|
|
|
444 |
|
|
|
445 |
\fBvoid png_set_compression_strategy (png_structp \fP\fIpng_ptr\fP\fB, int \fIstrategy\fP\fB);\fP
|
|
|
446 |
|
|
|
447 |
\fI\fB
|
|
|
448 |
|
|
|
449 |
\fBvoid png_set_compression_window_bits (png_structp \fP\fIpng_ptr\fP\fB, int \fIwindow_bits\fP\fB);\fP
|
|
|
450 |
|
|
|
451 |
\fI\fB
|
|
|
452 |
|
|
|
453 |
\fBvoid png_set_crc_action (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIcrit_action\fP\fB, int \fIancil_action\fP\fB);\fP
|
|
|
454 |
|
|
|
455 |
\fI\fB
|
|
|
456 |
|
|
|
457 |
\fBvoid png_set_dither (png_structp \fP\fIpng_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fP\fInum_palette\fP\fB, int \fP\fImaximum_colors\fP\fB, png_uint_16p \fP\fIhistogram\fP\fB, int \fIfull_dither\fP\fB);\fP
|
|
|
458 |
|
|
|
459 |
\fI\fB
|
|
|
460 |
|
|
|
461 |
\fBvoid png_set_error_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIerror_ptr\fP\fB, png_error_ptr \fP\fIerror_fn\fP\fB, png_error_ptr \fIwarning_fn\fP\fB);\fP
|
|
|
462 |
|
|
|
463 |
\fI\fB
|
|
|
464 |
|
|
|
465 |
\fBvoid png_set_expand (png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
466 |
|
|
|
467 |
\fI\fB
|
|
|
468 |
|
|
|
469 |
\fBvoid png_set_filler (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIfiller\fP\fB, int \fIflags\fP\fB);\fP
|
|
|
470 |
|
|
|
471 |
\fI\fB
|
|
|
472 |
|
|
|
473 |
\fBvoid png_set_filter (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fImethod\fP\fB, int \fIfilters\fP\fB);\fP
|
|
|
474 |
|
|
|
475 |
\fI\fB
|
|
|
476 |
|
|
|
477 |
\fBvoid png_set_filter_heuristics (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIheuristic_method\fP\fB, int \fP\fInum_weights\fP\fB, png_doublep \fP\fIfilter_weights\fP\fB, png_doublep \fIfilter_costs\fP\fB);\fP
|
|
|
478 |
|
|
|
479 |
\fI\fB
|
|
|
480 |
|
|
|
481 |
\fBvoid png_set_flush (png_structp \fP\fIpng_ptr\fP\fB, int \fInrows\fP\fB);\fP
|
|
|
482 |
|
|
|
483 |
\fI\fB
|
|
|
484 |
|
|
|
485 |
\fBvoid png_set_gamma (png_structp \fP\fIpng_ptr\fP\fB, double \fP\fIscreen_gamma\fP\fB, double \fIdefault_file_gamma\fP\fB);\fP
|
|
|
486 |
|
|
|
487 |
\fI\fB
|
|
|
488 |
|
|
|
489 |
\fBvoid png_set_gAMA (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, double \fIfile_gamma\fP\fB);\fP
|
|
|
490 |
|
|
|
491 |
\fI\fB
|
|
|
492 |
|
|
|
493 |
\fBvoid png_set_gAMA_fixed (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fIfile_gamma\fP\fB);\fP
|
|
|
494 |
|
|
|
495 |
\fI\fB
|
|
|
496 |
|
|
|
497 |
\fBvoid png_set_gray_1_2_4_to_8(png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
498 |
|
|
|
499 |
\fI\fB
|
|
|
500 |
|
|
|
501 |
\fBvoid png_set_gray_to_rgb (png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
502 |
|
|
|
503 |
\fI\fB
|
|
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504 |
|
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|
505 |
\fBvoid png_set_hIST (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_16p \fIhist\fP\fB);\fP
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506 |
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507 |
\fI\fB
|
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508 |
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|
509 |
\fBvoid png_set_iCCP (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIname\fP\fB, int \fP\fIcompression_type\fP\fB, png_charp \fP\fIprofile\fP\fB, png_uint_32 \fIproflen\fP\fB);\fP
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510 |
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|
511 |
\fI\fB
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512 |
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|
513 |
\fBint png_set_interlace_handling (png_structp \fIpng_ptr\fP\fB);\fP
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514 |
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515 |
\fI\fB
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516 |
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|
517 |
\fBvoid png_set_invalid (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fImask\fP\fB);\fP
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518 |
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|
519 |
\fI\fB
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|
520 |
|
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|
521 |
\fBvoid png_set_invert_alpha (png_structp \fIpng_ptr\fP\fB);\fP
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|
522 |
|
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|
523 |
\fI\fB
|
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|
524 |
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|
525 |
\fBvoid png_set_invert_mono (png_structp \fIpng_ptr\fP\fB);\fP
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526 |
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|
527 |
\fI\fB
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528 |
|
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|
529 |
\fBvoid png_set_IHDR (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIwidth\fP\fB, png_uint_32 \fP\fIheight\fP\fB, int \fP\fIbit_depth\fP\fB, int \fP\fIcolor_type\fP\fB, int \fP\fIinterlace_type\fP\fB, int \fP\fIcompression_type\fP\fB, int \fIfilter_type\fP\fB);\fP
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530 |
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|
531 |
\fI\fB
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532 |
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533 |
\fBvoid png_set_keep_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIkeep\fP\fB, png_bytep \fP\fIchunk_list\fP\fB, int \fInum_chunks\fP\fB);\fP
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534 |
|
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|
535 |
\fI\fB
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|
536 |
|
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|
537 |
\fBvoid png_set_mem_fn(png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fImem_ptr\fP\fB, png_malloc_ptr \fP\fImalloc_fn\fP\fB, png_free_ptr \fIfree_fn\fP\fB);\fP
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538 |
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|
539 |
\fI\fB
|
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540 |
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|
541 |
\fBvoid png_set_oFFs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIoffset_x\fP\fB, png_uint_32 \fP\fIoffset_y\fP\fB, int \fIunit_type\fP\fB);\fP
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|
542 |
|
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|
543 |
\fI\fB
|
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|
544 |
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|
545 |
\fBvoid png_set_packing (png_structp \fIpng_ptr\fP\fB);\fP
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546 |
|
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|
547 |
\fI\fB
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|
548 |
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|
549 |
\fBvoid png_set_packswap (png_structp \fIpng_ptr\fP\fB);\fP
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550 |
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|
551 |
\fI\fB
|
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|
552 |
|
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|
553 |
\fBvoid png_set_palette_to_rgb(png_structp \fIpng_ptr\fP\fB);\fP
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554 |
|
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|
555 |
\fI\fB
|
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|
556 |
|
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|
557 |
\fBvoid png_set_pCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIpurpose\fP\fB, png_int_32 \fP\fIX0\fP\fB, png_int_32 \fP\fIX1\fP\fB, int \fP\fItype\fP\fB, int \fP\fInparams\fP\fB, png_charp \fP\fIunits\fP\fB, png_charpp \fIparams\fP\fB);\fP
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558 |
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|
559 |
\fI\fB
|
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|
560 |
|
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|
561 |
\fBvoid png_set_pHYs (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_uint_32 \fP\fIres_x\fP\fB, png_uint_32 \fP\fIres_y\fP\fB, int \fIunit_type\fP\fB);\fP
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562 |
|
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|
563 |
\fI\fB
|
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|
564 |
|
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|
565 |
\fBvoid png_set_progressive_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIprogressive_ptr\fP\fB, png_progressive_info_ptr \fP\fIinfo_fn\fP\fB, png_progressive_row_ptr \fP\fIrow_fn\fP\fB, png_progressive_end_ptr \fIend_fn\fP\fB);\fP
|
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|
566 |
|
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|
567 |
\fI\fB
|
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|
568 |
|
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|
569 |
\fBvoid png_set_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_colorp \fP\fIpalette\fP\fB, int \fInum_palette\fP\fB);\fP
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|
570 |
|
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|
571 |
\fI\fB
|
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|
572 |
|
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|
573 |
\fBvoid png_set_read_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fIread_data_fn\fP\fB);\fP
|
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|
574 |
|
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|
575 |
\fI\fB
|
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|
576 |
|
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|
577 |
\fBvoid png_set_read_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_read_status_ptr \fIread_row_fn\fP\fB);\fP
|
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|
578 |
|
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|
579 |
\fI\fB
|
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|
580 |
|
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|
581 |
\fBvoid png_set_read_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIread_user_transform_fn\fP\fB);\fP
|
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|
582 |
|
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|
583 |
\fI\fB
|
|
|
584 |
|
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|
585 |
\fBvoid png_set_rgb_to_gray (png_structp \fP\fIpng_ptr\fP\fB, int \fP\fIerror_action\fP\fB, double \fP\fIred\fP\fB, double \fIgreen\fP\fB);\fP
|
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|
586 |
|
|
|
587 |
\fI\fB
|
|
|
588 |
|
|
|
589 |
\fBvoid png_set_rgb_to_gray_fixed (png_structp \fP\fIpng_ptr\fP\fB, int error_action png_fixed_point \fP\fIred\fP\fB, png_fixed_point \fIgreen\fP\fB);\fP
|
|
|
590 |
|
|
|
591 |
\fI\fB
|
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|
592 |
|
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|
593 |
\fBvoid png_set_rows (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytepp \fIrow_pointers\fP\fB);\fP
|
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|
594 |
|
|
|
595 |
\fI\fB
|
|
|
596 |
|
|
|
597 |
\fBvoid png_set_sBIT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_color_8p \fIsig_bit\fP\fB);\fP
|
|
|
598 |
|
|
|
599 |
\fI\fB
|
|
|
600 |
|
|
|
601 |
\fBvoid png_set_sCAL (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_charp \fP\fIunit\fP\fB, double \fP\fIwidth\fP\fB, double \fIheight\fP\fB);\fP
|
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|
602 |
|
|
|
603 |
\fI\fB
|
|
|
604 |
|
|
|
605 |
\fBvoid png_set_shift (png_structp \fP\fIpng_ptr\fP\fB, png_color_8p \fItrue_bits\fP\fB);\fP
|
|
|
606 |
|
|
|
607 |
\fI\fB
|
|
|
608 |
|
|
|
609 |
\fBvoid png_set_sig_bytes (png_structp \fP\fIpng_ptr\fP\fB, int \fInum_bytes\fP\fB);\fP
|
|
|
610 |
|
|
|
611 |
\fI\fB
|
|
|
612 |
|
|
|
613 |
\fBvoid png_set_sPLT (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_spalette_p \fP\fIsplt_ptr\fP\fB, int \fInum_spalettes\fP\fB);\fP
|
|
|
614 |
|
|
|
615 |
\fI\fB
|
|
|
616 |
|
|
|
617 |
\fBvoid png_set_sRGB (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
|
|
|
618 |
|
|
|
619 |
\fI\fB
|
|
|
620 |
|
|
|
621 |
\fBvoid png_set_sRGB_gAMA_and_cHRM (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fIintent\fP\fB);\fP
|
|
|
622 |
|
|
|
623 |
\fI\fB
|
|
|
624 |
|
|
|
625 |
\fBvoid png_set_strip_16 (png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
626 |
|
|
|
627 |
\fI\fB
|
|
|
628 |
|
|
|
629 |
\fBvoid png_set_strip_alpha (png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
630 |
|
|
|
631 |
\fI\fB
|
|
|
632 |
|
|
|
633 |
\fBvoid png_set_swap (png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
634 |
|
|
|
635 |
\fI\fB
|
|
|
636 |
|
|
|
637 |
\fBvoid png_set_swap_alpha (png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
638 |
|
|
|
639 |
\fI\fB
|
|
|
640 |
|
|
|
641 |
\fBvoid png_set_text (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_textp \fP\fItext_ptr\fP\fB, int \fInum_text\fP\fB);\fP
|
|
|
642 |
|
|
|
643 |
\fI\fB
|
|
|
644 |
|
|
|
645 |
\fBvoid png_set_tIME (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_timep \fImod_time\fP\fB);\fP
|
|
|
646 |
|
|
|
647 |
\fI\fB
|
|
|
648 |
|
|
|
649 |
\fBvoid png_set_tRNS (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_bytep \fP\fItrans\fP\fB, int \fP\fInum_trans\fP\fB, png_color_16p \fItrans_values\fP\fB);\fP
|
|
|
650 |
|
|
|
651 |
\fI\fB
|
|
|
652 |
|
|
|
653 |
\fBvoid png_set_tRNS_to_alpha(png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
654 |
|
|
|
655 |
\fI\fB
|
|
|
656 |
|
|
|
657 |
\fBpng_uint_32 png_set_unknown_chunks (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, png_unknown_chunkp \fP\fIunknowns\fP\fB, int \fP\fInum\fP\fB, int \fIlocation\fP\fB);\fP
|
|
|
658 |
|
|
|
659 |
\fI\fB
|
|
|
660 |
|
|
|
661 |
\fBvoid png_set_unknown_chunk_location(png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fIchunk\fP\fB, int \fIlocation\fP\fB);\fP
|
|
|
662 |
|
|
|
663 |
\fI\fB
|
|
|
664 |
|
|
|
665 |
\fBvoid png_set_read_user_chunk_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_chunk_ptr\fP\fB, png_user_chunk_ptr \fIread_user_chunk_fn\fP\fB);\fP
|
|
|
666 |
|
|
|
667 |
\fI\fB
|
|
|
668 |
|
|
|
669 |
\fBvoid png_set_user_limits (png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fP\fIuser_width_max\fP\fB, png_uint_32 \fIuser_height_max\fP\fB);\fP
|
|
|
670 |
|
|
|
671 |
\fI\fB
|
|
|
672 |
|
|
|
673 |
\fBvoid png_set_user_transform_info (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIuser_transform_ptr\fP\fB, int \fP\fIuser_transform_depth\fP\fB, int \fIuser_transform_channels\fP\fB);\fP
|
|
|
674 |
|
|
|
675 |
\fI\fB
|
|
|
676 |
|
|
|
677 |
\fBvoid png_set_write_fn (png_structp \fP\fIpng_ptr\fP\fB, png_voidp \fP\fIio_ptr\fP\fB, png_rw_ptr \fP\fIwrite_data_fn\fP\fB, png_flush_ptr \fIoutput_flush_fn\fP\fB);\fP
|
|
|
678 |
|
|
|
679 |
\fI\fB
|
|
|
680 |
|
|
|
681 |
\fBvoid png_set_write_status_fn (png_structp \fP\fIpng_ptr\fP\fB, png_write_status_ptr \fIwrite_row_fn\fP\fB);\fP
|
|
|
682 |
|
|
|
683 |
\fI\fB
|
|
|
684 |
|
|
|
685 |
\fBvoid png_set_write_user_transform_fn (png_structp \fP\fIpng_ptr\fP\fB, png_user_transform_ptr \fIwrite_user_transform_fn\fP\fB);\fP
|
|
|
686 |
|
|
|
687 |
\fI\fB
|
|
|
688 |
|
|
|
689 |
\fBvoid png_set_compression_buffer_size(png_structp \fP\fIpng_ptr\fP\fB, png_uint_32 \fIsize\fP\fB);\fP
|
|
|
690 |
|
|
|
691 |
\fI\fB
|
|
|
692 |
|
|
|
693 |
\fBint png_sig_cmp (png_bytep \fP\fIsig\fP\fB, png_size_t \fP\fIstart\fP\fB, png_size_t \fInum_to_check\fP\fB);\fP
|
|
|
694 |
|
|
|
695 |
\fI\fB
|
|
|
696 |
|
|
|
697 |
\fBvoid png_start_read_image (png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
698 |
|
|
|
699 |
\fI\fB
|
|
|
700 |
|
|
|
701 |
\fBvoid png_warning (png_structp \fP\fIpng_ptr\fP\fB, png_const_charp \fImessage\fP\fB);\fP
|
|
|
702 |
|
|
|
703 |
\fI\fB
|
|
|
704 |
|
|
|
705 |
\fBvoid png_write_chunk (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
|
|
|
706 |
|
|
|
707 |
\fI\fB
|
|
|
708 |
|
|
|
709 |
\fBvoid png_write_chunk_data (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIdata\fP\fB, png_size_t \fIlength\fP\fB);\fP
|
|
|
710 |
|
|
|
711 |
\fI\fB
|
|
|
712 |
|
|
|
713 |
\fBvoid png_write_chunk_end (png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
714 |
|
|
|
715 |
\fI\fB
|
|
|
716 |
|
|
|
717 |
\fBvoid png_write_chunk_start (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fP\fIchunk_name\fP\fB, png_uint_32 \fIlength\fP\fB);\fP
|
|
|
718 |
|
|
|
719 |
\fI\fB
|
|
|
720 |
|
|
|
721 |
\fBvoid png_write_destroy (png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
722 |
|
|
|
723 |
\fI\fB
|
|
|
724 |
|
|
|
725 |
\fBvoid png_write_end (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|
|
726 |
|
|
|
727 |
\fI\fB
|
|
|
728 |
|
|
|
729 |
\fBvoid png_write_flush (png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
730 |
|
|
|
731 |
\fI\fB
|
|
|
732 |
|
|
|
733 |
\fBvoid png_write_image (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fIimage\fP\fB);\fP
|
|
|
734 |
|
|
|
735 |
\fI\fB
|
|
|
736 |
|
|
|
737 |
\fBDEPRECATED: void png_write_init (png_structp \fIpng_ptr\fP\fB);\fP
|
|
|
738 |
|
|
|
739 |
\fI\fB
|
|
|
740 |
|
|
|
741 |
\fBDEPRECATED: void png_write_init_2 (png_structpp \fP\fIptr_ptr\fP\fB, png_const_charp \fP\fIuser_png_ver\fP\fB, png_size_t \fP\fIpng_struct_size\fP\fB, png_size_t \fIpng_info_size\fP\fB);\fP
|
|
|
742 |
|
|
|
743 |
\fI\fB
|
|
|
744 |
|
|
|
745 |
\fBvoid png_write_info (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|
|
746 |
|
|
|
747 |
\fI\fB
|
|
|
748 |
|
|
|
749 |
\fBvoid png_write_info_before_PLTE (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fIinfo_ptr\fP\fB);\fP
|
|
|
750 |
|
|
|
751 |
\fI\fB
|
|
|
752 |
|
|
|
753 |
\fBvoid png_write_png (png_structp \fP\fIpng_ptr\fP\fB, png_infop \fP\fIinfo_ptr\fP\fB, int \fP\fItransforms\fP\fB, png_voidp \fIparams\fP\fB);\fP
|
|
|
754 |
|
|
|
755 |
\fI\fB
|
|
|
756 |
|
|
|
757 |
\fBvoid png_write_row (png_structp \fP\fIpng_ptr\fP\fB, png_bytep \fIrow\fP\fB);\fP
|
|
|
758 |
|
|
|
759 |
\fI\fB
|
|
|
760 |
|
|
|
761 |
\fBvoid png_write_rows (png_structp \fP\fIpng_ptr\fP\fB, png_bytepp \fP\fIrow\fP\fB, png_uint_32 \fInum_rows\fP\fB);\fP
|
|
|
762 |
|
|
|
763 |
\fI\fB
|
|
|
764 |
|
|
|
765 |
\fBvoidpf png_zalloc (voidpf \fP\fIpng_ptr\fP\fB, uInt \fP\fIitems\fP\fB, uInt \fIsize\fP\fB);\fP
|
|
|
766 |
|
|
|
767 |
\fI\fB
|
|
|
768 |
|
|
|
769 |
\fBvoid png_zfree (voidpf \fP\fIpng_ptr\fP\fB, voidpf \fIptr\fP\fB);\fP
|
|
|
770 |
|
|
|
771 |
\fI\fB
|
|
|
772 |
|
|
|
773 |
.SH DESCRIPTION
|
|
|
774 |
The
|
|
|
775 |
.I libpng
|
|
|
776 |
library supports encoding, decoding, and various manipulations of
|
|
|
777 |
the Portable Network Graphics (PNG) format image files. It uses the
|
|
|
778 |
.IR zlib(3)
|
|
|
779 |
compression library.
|
|
|
780 |
Following is a copy of the libpng.txt file that accompanies libpng.
|
|
|
781 |
.SH LIBPNG.TXT
|
|
|
782 |
libpng.txt - A description on how to use and modify libpng
|
|
|
783 |
|
|
|
784 |
libpng version 1.2.8 - December 3, 2004
|
|
|
785 |
Updated and distributed by Glenn Randers-Pehrson
|
|
|
786 |
<glennrp at users.sourceforge.net>
|
|
|
787 |
Copyright (c) 1998-2004 Glenn Randers-Pehrson
|
|
|
788 |
For conditions of distribution and use, see copyright
|
|
|
789 |
notice in png.h.
|
|
|
790 |
|
|
|
791 |
based on:
|
|
|
792 |
|
|
|
793 |
libpng 1.0 beta 6 version 0.96 May 28, 1997
|
|
|
794 |
Updated and distributed by Andreas Dilger
|
|
|
795 |
Copyright (c) 1996, 1997 Andreas Dilger
|
|
|
796 |
|
|
|
797 |
libpng 1.0 beta 2 - version 0.88 January 26, 1996
|
|
|
798 |
For conditions of distribution and use, see copyright
|
|
|
799 |
notice in png.h. Copyright (c) 1995, 1996 Guy Eric
|
|
|
800 |
Schalnat, Group 42, Inc.
|
|
|
801 |
|
|
|
802 |
Updated/rewritten per request in the libpng FAQ
|
|
|
803 |
Copyright (c) 1995, 1996 Frank J. T. Wojcik
|
|
|
804 |
December 18, 1995 & January 20, 1996
|
|
|
805 |
|
|
|
806 |
.SH I. Introduction
|
|
|
807 |
|
|
|
808 |
This file describes how to use and modify the PNG reference library
|
|
|
809 |
(known as libpng) for your own use. There are five sections to this
|
|
|
810 |
file: introduction, structures, reading, writing, and modification and
|
|
|
811 |
configuration notes for various special platforms. In addition to this
|
|
|
812 |
file, example.c is a good starting point for using the library, as
|
|
|
813 |
it is heavily commented and should include everything most people
|
|
|
814 |
will need. We assume that libpng is already installed; see the
|
|
|
815 |
INSTALL file for instructions on how to install libpng.
|
|
|
816 |
|
|
|
817 |
Libpng was written as a companion to the PNG specification, as a way
|
|
|
818 |
of reducing the amount of time and effort it takes to support the PNG
|
|
|
819 |
file format in application programs.
|
|
|
820 |
|
|
|
821 |
The PNG specification (second edition), November 2003, is available as
|
|
|
822 |
a W3C Recommendation and as an ISO Standard (ISO/IEC 15948:2003 (E)) at
|
|
|
823 |
<http://www.w3.org/TR/2003/REC-PNG-20031110/
|
|
|
824 |
The W3C and ISO documents have identical technical content.
|
|
|
825 |
|
|
|
826 |
The PNG-1.2 specification is available at
|
|
|
827 |
<http://www.libpng.org/pub/png/documents/>
|
|
|
828 |
|
|
|
829 |
The PNG-1.0 specification is available
|
|
|
830 |
as RFC 2083 <http://www.libpng.org/pub/png/documents/> and as a
|
|
|
831 |
W3C Recommendation <http://www.w3.org/TR/REC.png.html>. Some
|
|
|
832 |
additional chunks are described in the special-purpose public chunks
|
|
|
833 |
documents at <http://www.libpng.org/pub/png/documents/>.
|
|
|
834 |
|
|
|
835 |
Other information
|
|
|
836 |
about PNG, and the latest version of libpng, can be found at the PNG home
|
|
|
837 |
page, <http://www.libpng.org/pub/png/>.
|
|
|
838 |
|
|
|
839 |
Most users will not have to modify the library significantly; advanced
|
|
|
840 |
users may want to modify it more. All attempts were made to make it as
|
|
|
841 |
complete as possible, while keeping the code easy to understand.
|
|
|
842 |
Currently, this library only supports C. Support for other languages
|
|
|
843 |
is being considered.
|
|
|
844 |
|
|
|
845 |
Libpng has been designed to handle multiple sessions at one time,
|
|
|
846 |
to be easily modifiable, to be portable to the vast majority of
|
|
|
847 |
machines (ANSI, K&R, 16-, 32-, and 64-bit) available, and to be easy
|
|
|
848 |
to use. The ultimate goal of libpng is to promote the acceptance of
|
|
|
849 |
the PNG file format in whatever way possible. While there is still
|
|
|
850 |
work to be done (see the TODO file), libpng should cover the
|
|
|
851 |
majority of the needs of its users.
|
|
|
852 |
|
|
|
853 |
Libpng uses zlib for its compression and decompression of PNG files.
|
|
|
854 |
Further information about zlib, and the latest version of zlib, can
|
|
|
855 |
be found at the zlib home page, <http://www.info-zip.org/pub/infozip/zlib/>.
|
|
|
856 |
The zlib compression utility is a general purpose utility that is
|
|
|
857 |
useful for more than PNG files, and can be used without libpng.
|
|
|
858 |
See the documentation delivered with zlib for more details.
|
|
|
859 |
You can usually find the source files for the zlib utility wherever you
|
|
|
860 |
find the libpng source files.
|
|
|
861 |
|
|
|
862 |
Libpng is thread safe, provided the threads are using different
|
|
|
863 |
instances of the structures. Each thread should have its own
|
|
|
864 |
png_struct and png_info instances, and thus its own image.
|
|
|
865 |
Libpng does not protect itself against two threads using the
|
|
|
866 |
same instance of a structure. Note: thread safety may be defeated
|
|
|
867 |
by use of some of the MMX assembler code in pnggccrd.c, which is only
|
|
|
868 |
compiled when the user defines PNG_THREAD_UNSAFE_OK.
|
|
|
869 |
|
|
|
870 |
.SH II. Structures
|
|
|
871 |
|
|
|
872 |
There are two main structures that are important to libpng, png_struct
|
|
|
873 |
and png_info. The first, png_struct, is an internal structure that
|
|
|
874 |
will not, for the most part, be used by a user except as the first
|
|
|
875 |
variable passed to every libpng function call.
|
|
|
876 |
|
|
|
877 |
The png_info structure is designed to provide information about the
|
|
|
878 |
PNG file. At one time, the fields of png_info were intended to be
|
|
|
879 |
directly accessible to the user. However, this tended to cause problems
|
|
|
880 |
with applications using dynamically loaded libraries, and as a result
|
|
|
881 |
a set of interface functions for png_info (the png_get_*() and png_set_*()
|
|
|
882 |
functions) was developed. The fields of png_info are still available for
|
|
|
883 |
older applications, but it is suggested that applications use the new
|
|
|
884 |
interfaces if at all possible.
|
|
|
885 |
|
|
|
886 |
Applications that do make direct access to the members of png_struct (except
|
|
|
887 |
for png_ptr->jmpbuf) must be recompiled whenever the library is updated,
|
|
|
888 |
and applications that make direct access to the members of png_info must
|
|
|
889 |
be recompiled if they were compiled or loaded with libpng version 1.0.6,
|
|
|
890 |
in which the members were in a different order. In version 1.0.7, the
|
|
|
891 |
members of the png_info structure reverted to the old order, as they were
|
|
|
892 |
in versions 0.97c through 1.0.5. Starting with version 2.0.0, both
|
|
|
893 |
structures are going to be hidden, and the contents of the structures will
|
|
|
894 |
only be accessible through the png_get/png_set functions.
|
|
|
895 |
|
|
|
896 |
The png.h header file is an invaluable reference for programming with libpng.
|
|
|
897 |
And while I'm on the topic, make sure you include the libpng header file:
|
|
|
898 |
|
|
|
899 |
#include <png.h>
|
|
|
900 |
|
|
|
901 |
.SH III. Reading
|
|
|
902 |
|
|
|
903 |
We'll now walk you through the possible functions to call when reading
|
|
|
904 |
in a PNG file sequentially, briefly explaining the syntax and purpose
|
|
|
905 |
of each one. See example.c and png.h for more detail. While
|
|
|
906 |
progressive reading is covered in the next section, you will still
|
|
|
907 |
need some of the functions discussed in this section to read a PNG
|
|
|
908 |
file.
|
|
|
909 |
|
|
|
910 |
.SS Setup
|
|
|
911 |
|
|
|
912 |
You will want to do the I/O initialization(*) before you get into libpng,
|
|
|
913 |
so if it doesn't work, you don't have much to undo. Of course, you
|
|
|
914 |
will also want to insure that you are, in fact, dealing with a PNG
|
|
|
915 |
file. Libpng provides a simple check to see if a file is a PNG file.
|
|
|
916 |
To use it, pass in the first 1 to 8 bytes of the file to the function
|
|
|
917 |
png_sig_cmp(), and it will return 0 if the bytes match the corresponding
|
|
|
918 |
bytes of the PNG signature, or nonzero otherwise. Of course, the more bytes
|
|
|
919 |
you pass in, the greater the accuracy of the prediction.
|
|
|
920 |
|
|
|
921 |
If you are intending to keep the file pointer open for use in libpng,
|
|
|
922 |
you must ensure you don't read more than 8 bytes from the beginning
|
|
|
923 |
of the file, and you also have to make a call to png_set_sig_bytes_read()
|
|
|
924 |
with the number of bytes you read from the beginning. Libpng will
|
|
|
925 |
then only check the bytes (if any) that your program didn't read.
|
|
|
926 |
|
|
|
927 |
(*): If you are not using the standard I/O functions, you will need
|
|
|
928 |
to replace them with custom functions. See the discussion under
|
|
|
929 |
Customizing libpng.
|
|
|
930 |
|
|
|
931 |
|
|
|
932 |
FILE *fp = fopen(file_name, "rb");
|
|
|
933 |
if (!fp)
|
|
|
934 |
{
|
|
|
935 |
return (ERROR);
|
|
|
936 |
}
|
|
|
937 |
fread(header, 1, number, fp);
|
|
|
938 |
is_png = !png_sig_cmp(header, 0, number);
|
|
|
939 |
if (!is_png)
|
|
|
940 |
{
|
|
|
941 |
return (NOT_PNG);
|
|
|
942 |
}
|
|
|
943 |
|
|
|
944 |
|
|
|
945 |
Next, png_struct and png_info need to be allocated and initialized. In
|
|
|
946 |
order to ensure that the size of these structures is correct even with a
|
|
|
947 |
dynamically linked libpng, there are functions to initialize and
|
|
|
948 |
allocate the structures. We also pass the library version, optional
|
|
|
949 |
pointers to error handling functions, and a pointer to a data struct for
|
|
|
950 |
use by the error functions, if necessary (the pointer and functions can
|
|
|
951 |
be NULL if the default error handlers are to be used). See the section
|
|
|
952 |
on Changes to Libpng below regarding the old initialization functions.
|
|
|
953 |
The structure allocation functions quietly return NULL if they fail to
|
|
|
954 |
create the structure, so your application should check for that.
|
|
|
955 |
|
|
|
956 |
png_structp png_ptr = png_create_read_struct
|
|
|
957 |
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
|
958 |
user_error_fn, user_warning_fn);
|
|
|
959 |
if (!png_ptr)
|
|
|
960 |
return (ERROR);
|
|
|
961 |
|
|
|
962 |
png_infop info_ptr = png_create_info_struct(png_ptr);
|
|
|
963 |
if (!info_ptr)
|
|
|
964 |
{
|
|
|
965 |
png_destroy_read_struct(&png_ptr,
|
|
|
966 |
(png_infopp)NULL, (png_infopp)NULL);
|
|
|
967 |
return (ERROR);
|
|
|
968 |
}
|
|
|
969 |
|
|
|
970 |
png_infop end_info = png_create_info_struct(png_ptr);
|
|
|
971 |
if (!end_info)
|
|
|
972 |
{
|
|
|
973 |
png_destroy_read_struct(&png_ptr, &info_ptr,
|
|
|
974 |
(png_infopp)NULL);
|
|
|
975 |
return (ERROR);
|
|
|
976 |
}
|
|
|
977 |
|
|
|
978 |
If you want to use your own memory allocation routines,
|
|
|
979 |
define PNG_USER_MEM_SUPPORTED and use
|
|
|
980 |
png_create_read_struct_2() instead of png_create_read_struct():
|
|
|
981 |
|
|
|
982 |
png_structp png_ptr = png_create_read_struct_2
|
|
|
983 |
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
|
984 |
user_error_fn, user_warning_fn, (png_voidp)
|
|
|
985 |
user_mem_ptr, user_malloc_fn, user_free_fn);
|
|
|
986 |
|
|
|
987 |
The error handling routines passed to png_create_read_struct()
|
|
|
988 |
and the memory alloc/free routines passed to png_create_struct_2()
|
|
|
989 |
are only necessary if you are not using the libpng supplied error
|
|
|
990 |
handling and memory alloc/free functions.
|
|
|
991 |
|
|
|
992 |
When libpng encounters an error, it expects to longjmp back
|
|
|
993 |
to your routine. Therefore, you will need to call setjmp and pass
|
|
|
994 |
your png_jmpbuf(png_ptr). If you read the file from different
|
|
|
995 |
routines, you will need to update the jmpbuf field every time you enter
|
|
|
996 |
a new routine that will call a png_*() function.
|
|
|
997 |
|
|
|
998 |
See your documentation of setjmp/longjmp for your compiler for more
|
|
|
999 |
information on setjmp/longjmp. See the discussion on libpng error
|
|
|
1000 |
handling in the Customizing Libpng section below for more information
|
|
|
1001 |
on the libpng error handling. If an error occurs, and libpng longjmp's
|
|
|
1002 |
back to your setjmp, you will want to call png_destroy_read_struct() to
|
|
|
1003 |
free any memory.
|
|
|
1004 |
|
|
|
1005 |
if (setjmp(png_jmpbuf(png_ptr)))
|
|
|
1006 |
{
|
|
|
1007 |
png_destroy_read_struct(&png_ptr, &info_ptr,
|
|
|
1008 |
&end_info);
|
|
|
1009 |
fclose(fp);
|
|
|
1010 |
return (ERROR);
|
|
|
1011 |
}
|
|
|
1012 |
|
|
|
1013 |
If you would rather avoid the complexity of setjmp/longjmp issues,
|
|
|
1014 |
you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
|
|
|
1015 |
errors will result in a call to PNG_ABORT() which defaults to abort().
|
|
|
1016 |
|
|
|
1017 |
Now you need to set up the input code. The default for libpng is to
|
|
|
1018 |
use the C function fread(). If you use this, you will need to pass a
|
|
|
1019 |
valid FILE * in the function png_init_io(). Be sure that the file is
|
|
|
1020 |
opened in binary mode. If you wish to handle reading data in another
|
|
|
1021 |
way, you need not call the png_init_io() function, but you must then
|
|
|
1022 |
implement the libpng I/O methods discussed in the Customizing Libpng
|
|
|
1023 |
section below.
|
|
|
1024 |
|
|
|
1025 |
png_init_io(png_ptr, fp);
|
|
|
1026 |
|
|
|
1027 |
If you had previously opened the file and read any of the signature from
|
|
|
1028 |
the beginning in order to see if this was a PNG file, you need to let
|
|
|
1029 |
libpng know that there are some bytes missing from the start of the file.
|
|
|
1030 |
|
|
|
1031 |
png_set_sig_bytes(png_ptr, number);
|
|
|
1032 |
|
|
|
1033 |
.SS Setting up callback code
|
|
|
1034 |
|
|
|
1035 |
You can set up a callback function to handle any unknown chunks in the
|
|
|
1036 |
input stream. You must supply the function
|
|
|
1037 |
|
|
|
1038 |
read_chunk_callback(png_ptr ptr,
|
|
|
1039 |
png_unknown_chunkp chunk);
|
|
|
1040 |
{
|
|
|
1041 |
/* The unknown chunk structure contains your
|
|
|
1042 |
chunk data: */
|
|
|
1043 |
png_byte name[5];
|
|
|
1044 |
png_byte *data;
|
|
|
1045 |
png_size_t size;
|
|
|
1046 |
/* Note that libpng has already taken care of
|
|
|
1047 |
the CRC handling */
|
|
|
1048 |
|
|
|
1049 |
/* put your code here. Return one of the
|
|
|
1050 |
following: */
|
|
|
1051 |
|
|
|
1052 |
return (-n); /* chunk had an error */
|
|
|
1053 |
return (0); /* did not recognize */
|
|
|
1054 |
return (n); /* success */
|
|
|
1055 |
}
|
|
|
1056 |
|
|
|
1057 |
(You can give your function another name that you like instead of
|
|
|
1058 |
"read_chunk_callback")
|
|
|
1059 |
|
|
|
1060 |
To inform libpng about your function, use
|
|
|
1061 |
|
|
|
1062 |
png_set_read_user_chunk_fn(png_ptr, user_chunk_ptr,
|
|
|
1063 |
read_chunk_callback);
|
|
|
1064 |
|
|
|
1065 |
This names not only the callback function, but also a user pointer that
|
|
|
1066 |
you can retrieve with
|
|
|
1067 |
|
|
|
1068 |
png_get_user_chunk_ptr(png_ptr);
|
|
|
1069 |
|
|
|
1070 |
At this point, you can set up a callback function that will be
|
|
|
1071 |
called after each row has been read, which you can use to control
|
|
|
1072 |
a progress meter or the like. It's demonstrated in pngtest.c.
|
|
|
1073 |
You must supply a function
|
|
|
1074 |
|
|
|
1075 |
void read_row_callback(png_ptr ptr, png_uint_32 row,
|
|
|
1076 |
int pass);
|
|
|
1077 |
{
|
|
|
1078 |
/* put your code here */
|
|
|
1079 |
}
|
|
|
1080 |
|
|
|
1081 |
(You can give it another name that you like instead of "read_row_callback")
|
|
|
1082 |
|
|
|
1083 |
To inform libpng about your function, use
|
|
|
1084 |
|
|
|
1085 |
png_set_read_status_fn(png_ptr, read_row_callback);
|
|
|
1086 |
|
|
|
1087 |
.SS Width and height limits
|
|
|
1088 |
|
|
|
1089 |
The PNG specification allows the width and height of an image to be as
|
|
|
1090 |
large as 2^31-1 (0x7fffffff), or about 2.147 billion rows and columns.
|
|
|
1091 |
Since very few applications really need to process such large images,
|
|
|
1092 |
we have imposed an arbitrary 1-million limit on rows and columns.
|
|
|
1093 |
Larger images will be rejected immediately with a png_error() call. If
|
|
|
1094 |
you wish to override this limit, you can use
|
|
|
1095 |
|
|
|
1096 |
png_set_user_limits(png_ptr, width_max, height_max);
|
|
|
1097 |
|
|
|
1098 |
to set your own limits, or use width_max = height_max = 0x7fffffffL
|
|
|
1099 |
to allow all valid dimensions (libpng may reject some very large images
|
|
|
1100 |
anyway because of potential buffer overflow conditions).
|
|
|
1101 |
|
|
|
1102 |
You should put this statement after you create the PNG structure and
|
|
|
1103 |
before calling png_read_info(), png_read_png(), or png_process_data().
|
|
|
1104 |
If you need to retrieve the limits that are being applied, use
|
|
|
1105 |
|
|
|
1106 |
width_max = png_get_user_width_max(png_ptr);
|
|
|
1107 |
height_max = png_get_user_height_max(png_ptr);
|
|
|
1108 |
|
|
|
1109 |
.SS Unknown-chunk handling
|
|
|
1110 |
|
|
|
1111 |
Now you get to set the way the library processes unknown chunks in the
|
|
|
1112 |
input PNG stream. Both known and unknown chunks will be read. Normal
|
|
|
1113 |
behavior is that known chunks will be parsed into information in
|
|
|
1114 |
various info_ptr members; unknown chunks will be discarded. To change
|
|
|
1115 |
this, you can call:
|
|
|
1116 |
|
|
|
1117 |
png_set_keep_unknown_chunks(png_ptr, keep,
|
|
|
1118 |
chunk_list, num_chunks);
|
|
|
1119 |
keep - 0: do not handle as unknown
|
|
|
1120 |
1: do not keep
|
|
|
1121 |
2: keep only if safe-to-copy
|
|
|
1122 |
3: keep even if unsafe-to-copy
|
|
|
1123 |
You can use these definitions:
|
|
|
1124 |
PNG_HANDLE_CHUNK_AS_DEFAULT 0
|
|
|
1125 |
PNG_HANDLE_CHUNK_NEVER 1
|
|
|
1126 |
PNG_HANDLE_CHUNK_IF_SAFE 2
|
|
|
1127 |
PNG_HANDLE_CHUNK_ALWAYS 3
|
|
|
1128 |
chunk_list - list of chunks affected (a byte string,
|
|
|
1129 |
five bytes per chunk, NULL or '\0' if
|
|
|
1130 |
num_chunks is 0)
|
|
|
1131 |
num_chunks - number of chunks affected; if 0, all
|
|
|
1132 |
unknown chunks are affected. If nonzero,
|
|
|
1133 |
only the chunks in the list are affected
|
|
|
1134 |
|
|
|
1135 |
Unknown chunks declared in this way will be saved as raw data onto a
|
|
|
1136 |
list of png_unknown_chunk structures. If a chunk that is normally
|
|
|
1137 |
known to libpng is named in the list, it will be handled as unknown,
|
|
|
1138 |
according to the "keep" directive. If a chunk is named in successive
|
|
|
1139 |
instances of png_set_keep_unknown_chunks(), the final instance will
|
|
|
1140 |
take precedence. The IHDR and IEND chunks should not be named in
|
|
|
1141 |
chunk_list; if they are, libpng will process them normally anyway.
|
|
|
1142 |
|
|
|
1143 |
.SS The high-level read interface
|
|
|
1144 |
|
|
|
1145 |
At this point there are two ways to proceed; through the high-level
|
|
|
1146 |
read interface, or through a sequence of low-level read operations.
|
|
|
1147 |
You can use the high-level interface if (a) you are willing to read
|
|
|
1148 |
the entire image into memory, and (b) the input transformations
|
|
|
1149 |
you want to do are limited to the following set:
|
|
|
1150 |
|
|
|
1151 |
PNG_TRANSFORM_IDENTITY No transformation
|
|
|
1152 |
PNG_TRANSFORM_STRIP_16 Strip 16-bit samples to
|
|
|
1153 |
8 bits
|
|
|
1154 |
PNG_TRANSFORM_STRIP_ALPHA Discard the alpha channel
|
|
|
1155 |
PNG_TRANSFORM_PACKING Expand 1, 2 and 4-bit
|
|
|
1156 |
samples to bytes
|
|
|
1157 |
PNG_TRANSFORM_PACKSWAP Change order of packed
|
|
|
1158 |
pixels to LSB first
|
|
|
1159 |
PNG_TRANSFORM_EXPAND Perform set_expand()
|
|
|
1160 |
PNG_TRANSFORM_INVERT_MONO Invert monochrome images
|
|
|
1161 |
PNG_TRANSFORM_SHIFT Normalize pixels to the
|
|
|
1162 |
sBIT depth
|
|
|
1163 |
PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
|
|
|
1164 |
to BGRA
|
|
|
1165 |
PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
|
|
|
1166 |
to AG
|
|
|
1167 |
PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
|
|
|
1168 |
to transparency
|
|
|
1169 |
PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
|
|
|
1170 |
|
|
|
1171 |
(This excludes setting a background color, doing gamma transformation,
|
|
|
1172 |
dithering, and setting filler.) If this is the case, simply do this:
|
|
|
1173 |
|
|
|
1174 |
png_read_png(png_ptr, info_ptr, png_transforms, NULL)
|
|
|
1175 |
|
|
|
1176 |
where png_transforms is an integer containing the logical OR of
|
|
|
1177 |
some set of transformation flags. This call is equivalent to png_read_info(),
|
|
|
1178 |
followed the set of transformations indicated by the transform mask,
|
|
|
1179 |
then png_read_image(), and finally png_read_end().
|
|
|
1180 |
|
|
|
1181 |
(The final parameter of this call is not yet used. Someday it might point
|
|
|
1182 |
to transformation parameters required by some future input transform.)
|
|
|
1183 |
|
|
|
1184 |
You must use png_transforms and not call any png_set_transform() functions
|
|
|
1185 |
when you use png_read_png().
|
|
|
1186 |
|
|
|
1187 |
After you have called png_read_png(), you can retrieve the image data
|
|
|
1188 |
with
|
|
|
1189 |
|
|
|
1190 |
row_pointers = png_get_rows(png_ptr, info_ptr);
|
|
|
1191 |
|
|
|
1192 |
where row_pointers is an array of pointers to the pixel data for each row:
|
|
|
1193 |
|
|
|
1194 |
png_bytep row_pointers[height];
|
|
|
1195 |
|
|
|
1196 |
If you know your image size and pixel size ahead of time, you can allocate
|
|
|
1197 |
row_pointers prior to calling png_read_png() with
|
|
|
1198 |
|
|
|
1199 |
if (height > PNG_UINT_32_MAX/png_sizeof(png_byte))
|
|
|
1200 |
png_error (png_ptr,
|
|
|
1201 |
"Image is too tall to process in memory");
|
|
|
1202 |
if (width > PNG_UINT_32_MAX/pixel_size)
|
|
|
1203 |
png_error (png_ptr,
|
|
|
1204 |
"Image is too wide to process in memory");
|
|
|
1205 |
row_pointers = png_malloc(png_ptr,
|
|
|
1206 |
height*png_sizeof(png_bytep));
|
|
|
1207 |
for (int i=0; i<height, i++)
|
|
|
1208 |
row_pointers[i]=png_malloc(png_ptr,
|
|
|
1209 |
width*pixel_size);
|
|
|
1210 |
png_set_rows(png_ptr, info_ptr, &row_pointers);
|
|
|
1211 |
|
|
|
1212 |
Alternatively you could allocate your image in one big block and define
|
|
|
1213 |
row_pointers[i] to point into the proper places in your block.
|
|
|
1214 |
|
|
|
1215 |
If you use png_set_rows(), the application is responsible for freeing
|
|
|
1216 |
row_pointers (and row_pointers[i], if they were separately allocated).
|
|
|
1217 |
|
|
|
1218 |
If you don't allocate row_pointers ahead of time, png_read_png() will
|
|
|
1219 |
do it, and it'll be free'ed when you call png_destroy_*().
|
|
|
1220 |
|
|
|
1221 |
.SS The low-level read interface
|
|
|
1222 |
|
|
|
1223 |
If you are going the low-level route, you are now ready to read all
|
|
|
1224 |
the file information up to the actual image data. You do this with a
|
|
|
1225 |
call to png_read_info().
|
|
|
1226 |
|
|
|
1227 |
png_read_info(png_ptr, info_ptr);
|
|
|
1228 |
|
|
|
1229 |
This will process all chunks up to but not including the image data.
|
|
|
1230 |
|
|
|
1231 |
.SS Querying the info structure
|
|
|
1232 |
|
|
|
1233 |
Functions are used to get the information from the info_ptr once it
|
|
|
1234 |
has been read. Note that these fields may not be completely filled
|
|
|
1235 |
in until png_read_end() has read the chunk data following the image.
|
|
|
1236 |
|
|
|
1237 |
png_get_IHDR(png_ptr, info_ptr, &width, &height,
|
|
|
1238 |
&bit_depth, &color_type, &interlace_type,
|
|
|
1239 |
&compression_type, &filter_method);
|
|
|
1240 |
|
|
|
1241 |
width - holds the width of the image
|
|
|
1242 |
in pixels (up to 2^31).
|
|
|
1243 |
height - holds the height of the image
|
|
|
1244 |
in pixels (up to 2^31).
|
|
|
1245 |
bit_depth - holds the bit depth of one of the
|
|
|
1246 |
image channels. (valid values are
|
|
|
1247 |
1, 2, 4, 8, 16 and depend also on
|
|
|
1248 |
the color_type. See also
|
|
|
1249 |
significant bits (sBIT) below).
|
|
|
1250 |
color_type - describes which color/alpha channels
|
|
|
1251 |
are present.
|
|
|
1252 |
PNG_COLOR_TYPE_GRAY
|
|
|
1253 |
(bit depths 1, 2, 4, 8, 16)
|
|
|
1254 |
PNG_COLOR_TYPE_GRAY_ALPHA
|
|
|
1255 |
(bit depths 8, 16)
|
|
|
1256 |
PNG_COLOR_TYPE_PALETTE
|
|
|
1257 |
(bit depths 1, 2, 4, 8)
|
|
|
1258 |
PNG_COLOR_TYPE_RGB
|
|
|
1259 |
(bit_depths 8, 16)
|
|
|
1260 |
PNG_COLOR_TYPE_RGB_ALPHA
|
|
|
1261 |
(bit_depths 8, 16)
|
|
|
1262 |
|
|
|
1263 |
PNG_COLOR_MASK_PALETTE
|
|
|
1264 |
PNG_COLOR_MASK_COLOR
|
|
|
1265 |
PNG_COLOR_MASK_ALPHA
|
|
|
1266 |
|
|
|
1267 |
filter_method - (must be PNG_FILTER_TYPE_BASE
|
|
|
1268 |
for PNG 1.0, and can also be
|
|
|
1269 |
PNG_INTRAPIXEL_DIFFERENCING if
|
|
|
1270 |
the PNG datastream is embedded in
|
|
|
1271 |
a MNG-1.0 datastream)
|
|
|
1272 |
compression_type - (must be PNG_COMPRESSION_TYPE_BASE
|
|
|
1273 |
for PNG 1.0)
|
|
|
1274 |
interlace_type - (PNG_INTERLACE_NONE or
|
|
|
1275 |
PNG_INTERLACE_ADAM7)
|
|
|
1276 |
Any or all of interlace_type, compression_type, of
|
|
|
1277 |
filter_method can be NULL if you are
|
|
|
1278 |
not interested in their values.
|
|
|
1279 |
|
|
|
1280 |
channels = png_get_channels(png_ptr, info_ptr);
|
|
|
1281 |
channels - number of channels of info for the
|
|
|
1282 |
color type (valid values are 1 (GRAY,
|
|
|
1283 |
PALETTE), 2 (GRAY_ALPHA), 3 (RGB),
|
|
|
1284 |
4 (RGB_ALPHA or RGB + filler byte))
|
|
|
1285 |
rowbytes = png_get_rowbytes(png_ptr, info_ptr);
|
|
|
1286 |
rowbytes - number of bytes needed to hold a row
|
|
|
1287 |
|
|
|
1288 |
signature = png_get_signature(png_ptr, info_ptr);
|
|
|
1289 |
signature - holds the signature read from the
|
|
|
1290 |
file (if any). The data is kept in
|
|
|
1291 |
the same offset it would be if the
|
|
|
1292 |
whole signature were read (i.e. if an
|
|
|
1293 |
application had already read in 4
|
|
|
1294 |
bytes of signature before starting
|
|
|
1295 |
libpng, the remaining 4 bytes would
|
|
|
1296 |
be in signature[4] through signature[7]
|
|
|
1297 |
(see png_set_sig_bytes())).
|
|
|
1298 |
|
|
|
1299 |
|
|
|
1300 |
width = png_get_image_width(png_ptr,
|
|
|
1301 |
info_ptr);
|
|
|
1302 |
height = png_get_image_height(png_ptr,
|
|
|
1303 |
info_ptr);
|
|
|
1304 |
bit_depth = png_get_bit_depth(png_ptr,
|
|
|
1305 |
info_ptr);
|
|
|
1306 |
color_type = png_get_color_type(png_ptr,
|
|
|
1307 |
info_ptr);
|
|
|
1308 |
filter_method = png_get_filter_type(png_ptr,
|
|
|
1309 |
info_ptr);
|
|
|
1310 |
compression_type = png_get_compression_type(png_ptr,
|
|
|
1311 |
info_ptr);
|
|
|
1312 |
interlace_type = png_get_interlace_type(png_ptr,
|
|
|
1313 |
info_ptr);
|
|
|
1314 |
|
|
|
1315 |
|
|
|
1316 |
These are also important, but their validity depends on whether the chunk
|
|
|
1317 |
has been read. The png_get_valid(png_ptr, info_ptr, PNG_INFO_<chunk>) and
|
|
|
1318 |
png_get_<chunk>(png_ptr, info_ptr, ...) functions return non-zero if the
|
|
|
1319 |
data has been read, or zero if it is missing. The parameters to the
|
|
|
1320 |
png_get_<chunk> are set directly if they are simple data types, or a pointer
|
|
|
1321 |
into the info_ptr is returned for any complex types.
|
|
|
1322 |
|
|
|
1323 |
png_get_PLTE(png_ptr, info_ptr, &palette,
|
|
|
1324 |
&num_palette);
|
|
|
1325 |
palette - the palette for the file
|
|
|
1326 |
(array of png_color)
|
|
|
1327 |
num_palette - number of entries in the palette
|
|
|
1328 |
|
|
|
1329 |
png_get_gAMA(png_ptr, info_ptr, &gamma);
|
|
|
1330 |
gamma - the gamma the file is written
|
|
|
1331 |
at (PNG_INFO_gAMA)
|
|
|
1332 |
|
|
|
1333 |
png_get_sRGB(png_ptr, info_ptr, &srgb_intent);
|
|
|
1334 |
srgb_intent - the rendering intent (PNG_INFO_sRGB)
|
|
|
1335 |
The presence of the sRGB chunk
|
|
|
1336 |
means that the pixel data is in the
|
|
|
1337 |
sRGB color space. This chunk also
|
|
|
1338 |
implies specific values of gAMA and
|
|
|
1339 |
cHRM.
|
|
|
1340 |
|
|
|
1341 |
png_get_iCCP(png_ptr, info_ptr, &name,
|
|
|
1342 |
&compression_type, &profile, &proflen);
|
|
|
1343 |
name - The profile name.
|
|
|
1344 |
compression - The compression type; always
|
|
|
1345 |
PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
|
|
|
1346 |
You may give NULL to this argument to
|
|
|
1347 |
ignore it.
|
|
|
1348 |
profile - International Color Consortium color
|
|
|
1349 |
profile data. May contain NULs.
|
|
|
1350 |
proflen - length of profile data in bytes.
|
|
|
1351 |
|
|
|
1352 |
png_get_sBIT(png_ptr, info_ptr, &sig_bit);
|
|
|
1353 |
sig_bit - the number of significant bits for
|
|
|
1354 |
(PNG_INFO_sBIT) each of the gray,
|
|
|
1355 |
red, green, and blue channels,
|
|
|
1356 |
whichever are appropriate for the
|
|
|
1357 |
given color type (png_color_16)
|
|
|
1358 |
|
|
|
1359 |
png_get_tRNS(png_ptr, info_ptr, &trans, &num_trans,
|
|
|
1360 |
&trans_values);
|
|
|
1361 |
trans - array of transparent entries for
|
|
|
1362 |
palette (PNG_INFO_tRNS)
|
|
|
1363 |
trans_values - graylevel or color sample values of
|
|
|
1364 |
the single transparent color for
|
|
|
1365 |
non-paletted images (PNG_INFO_tRNS)
|
|
|
1366 |
num_trans - number of transparent entries
|
|
|
1367 |
(PNG_INFO_tRNS)
|
|
|
1368 |
|
|
|
1369 |
png_get_hIST(png_ptr, info_ptr, &hist);
|
|
|
1370 |
(PNG_INFO_hIST)
|
|
|
1371 |
hist - histogram of palette (array of
|
|
|
1372 |
png_uint_16)
|
|
|
1373 |
|
|
|
1374 |
png_get_tIME(png_ptr, info_ptr, &mod_time);
|
|
|
1375 |
mod_time - time image was last modified
|
|
|
1376 |
(PNG_VALID_tIME)
|
|
|
1377 |
|
|
|
1378 |
png_get_bKGD(png_ptr, info_ptr, &background);
|
|
|
1379 |
background - background color (PNG_VALID_bKGD)
|
|
|
1380 |
valid 16-bit red, green and blue
|
|
|
1381 |
values, regardless of color_type
|
|
|
1382 |
|
|
|
1383 |
num_comments = png_get_text(png_ptr, info_ptr,
|
|
|
1384 |
&text_ptr, &num_text);
|
|
|
1385 |
num_comments - number of comments
|
|
|
1386 |
text_ptr - array of png_text holding image
|
|
|
1387 |
comments
|
|
|
1388 |
text_ptr[i].compression - type of compression used
|
|
|
1389 |
on "text" PNG_TEXT_COMPRESSION_NONE
|
|
|
1390 |
PNG_TEXT_COMPRESSION_zTXt
|
|
|
1391 |
PNG_ITXT_COMPRESSION_NONE
|
|
|
1392 |
PNG_ITXT_COMPRESSION_zTXt
|
|
|
1393 |
text_ptr[i].key - keyword for comment. Must contain
|
|
|
1394 |
1-79 characters.
|
|
|
1395 |
text_ptr[i].text - text comments for current
|
|
|
1396 |
keyword. Can be empty.
|
|
|
1397 |
text_ptr[i].text_length - length of text string,
|
|
|
1398 |
after decompression, 0 for iTXt
|
|
|
1399 |
text_ptr[i].itxt_length - length of itxt string,
|
|
|
1400 |
after decompression, 0 for tEXt/zTXt
|
|
|
1401 |
text_ptr[i].lang - language of comment (empty
|
|
|
1402 |
string for unknown).
|
|
|
1403 |
text_ptr[i].lang_key - keyword in UTF-8
|
|
|
1404 |
(empty string for unknown).
|
|
|
1405 |
num_text - number of comments (same as
|
|
|
1406 |
num_comments; you can put NULL here
|
|
|
1407 |
to avoid the duplication)
|
|
|
1408 |
Note while png_set_text() will accept text, language,
|
|
|
1409 |
and translated keywords that can be NULL pointers, the
|
|
|
1410 |
structure returned by png_get_text will always contain
|
|
|
1411 |
regular zero-terminated C strings. They might be
|
|
|
1412 |
empty strings but they will never be NULL pointers.
|
|
|
1413 |
|
|
|
1414 |
num_spalettes = png_get_sPLT(png_ptr, info_ptr,
|
|
|
1415 |
&palette_ptr);
|
|
|
1416 |
palette_ptr - array of palette structures holding
|
|
|
1417 |
contents of one or more sPLT chunks
|
|
|
1418 |
read.
|
|
|
1419 |
num_spalettes - number of sPLT chunks read.
|
|
|
1420 |
|
|
|
1421 |
png_get_oFFs(png_ptr, info_ptr, &offset_x, &offset_y,
|
|
|
1422 |
&unit_type);
|
|
|
1423 |
offset_x - positive offset from the left edge
|
|
|
1424 |
of the screen
|
|
|
1425 |
offset_y - positive offset from the top edge
|
|
|
1426 |
of the screen
|
|
|
1427 |
unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
|
|
|
1428 |
|
|
|
1429 |
png_get_pHYs(png_ptr, info_ptr, &res_x, &res_y,
|
|
|
1430 |
&unit_type);
|
|
|
1431 |
res_x - pixels/unit physical resolution in
|
|
|
1432 |
x direction
|
|
|
1433 |
res_y - pixels/unit physical resolution in
|
|
|
1434 |
x direction
|
|
|
1435 |
unit_type - PNG_RESOLUTION_UNKNOWN,
|
|
|
1436 |
PNG_RESOLUTION_METER
|
|
|
1437 |
|
|
|
1438 |
png_get_sCAL(png_ptr, info_ptr, &unit, &width,
|
|
|
1439 |
&height)
|
|
|
1440 |
unit - physical scale units (an integer)
|
|
|
1441 |
width - width of a pixel in physical scale units
|
|
|
1442 |
height - height of a pixel in physical scale units
|
|
|
1443 |
(width and height are doubles)
|
|
|
1444 |
|
|
|
1445 |
png_get_sCAL_s(png_ptr, info_ptr, &unit, &width,
|
|
|
1446 |
&height)
|
|
|
1447 |
unit - physical scale units (an integer)
|
|
|
1448 |
width - width of a pixel in physical scale units
|
|
|
1449 |
height - height of a pixel in physical scale units
|
|
|
1450 |
(width and height are strings like "2.54")
|
|
|
1451 |
|
|
|
1452 |
num_unknown_chunks = png_get_unknown_chunks(png_ptr,
|
|
|
1453 |
info_ptr, &unknowns)
|
|
|
1454 |
unknowns - array of png_unknown_chunk
|
|
|
1455 |
structures holding unknown chunks
|
|
|
1456 |
unknowns[i].name - name of unknown chunk
|
|
|
1457 |
unknowns[i].data - data of unknown chunk
|
|
|
1458 |
unknowns[i].size - size of unknown chunk's data
|
|
|
1459 |
unknowns[i].location - position of chunk in file
|
|
|
1460 |
|
|
|
1461 |
The value of "i" corresponds to the order in which the
|
|
|
1462 |
chunks were read from the PNG file or inserted with the
|
|
|
1463 |
png_set_unknown_chunks() function.
|
|
|
1464 |
|
|
|
1465 |
The data from the pHYs chunk can be retrieved in several convenient
|
|
|
1466 |
forms:
|
|
|
1467 |
|
|
|
1468 |
res_x = png_get_x_pixels_per_meter(png_ptr,
|
|
|
1469 |
info_ptr)
|
|
|
1470 |
res_y = png_get_y_pixels_per_meter(png_ptr,
|
|
|
1471 |
info_ptr)
|
|
|
1472 |
res_x_and_y = png_get_pixels_per_meter(png_ptr,
|
|
|
1473 |
info_ptr)
|
|
|
1474 |
res_x = png_get_x_pixels_per_inch(png_ptr,
|
|
|
1475 |
info_ptr)
|
|
|
1476 |
res_y = png_get_y_pixels_per_inch(png_ptr,
|
|
|
1477 |
info_ptr)
|
|
|
1478 |
res_x_and_y = png_get_pixels_per_inch(png_ptr,
|
|
|
1479 |
info_ptr)
|
|
|
1480 |
aspect_ratio = png_get_pixel_aspect_ratio(png_ptr,
|
|
|
1481 |
info_ptr)
|
|
|
1482 |
|
|
|
1483 |
(Each of these returns 0 [signifying "unknown"] if
|
|
|
1484 |
the data is not present or if res_x is 0;
|
|
|
1485 |
res_x_and_y is 0 if res_x != res_y)
|
|
|
1486 |
|
|
|
1487 |
The data from the oFFs chunk can be retrieved in several convenient
|
|
|
1488 |
forms:
|
|
|
1489 |
|
|
|
1490 |
x_offset = png_get_x_offset_microns(png_ptr, info_ptr);
|
|
|
1491 |
y_offset = png_get_y_offset_microns(png_ptr, info_ptr);
|
|
|
1492 |
x_offset = png_get_x_offset_inches(png_ptr, info_ptr);
|
|
|
1493 |
y_offset = png_get_y_offset_inches(png_ptr, info_ptr);
|
|
|
1494 |
|
|
|
1495 |
(Each of these returns 0 [signifying "unknown" if both
|
|
|
1496 |
x and y are 0] if the data is not present or if the
|
|
|
1497 |
chunk is present but the unit is the pixel)
|
|
|
1498 |
|
|
|
1499 |
For more information, see the png_info definition in png.h and the
|
|
|
1500 |
PNG specification for chunk contents. Be careful with trusting
|
|
|
1501 |
rowbytes, as some of the transformations could increase the space
|
|
|
1502 |
needed to hold a row (expand, filler, gray_to_rgb, etc.).
|
|
|
1503 |
See png_read_update_info(), below.
|
|
|
1504 |
|
|
|
1505 |
A quick word about text_ptr and num_text. PNG stores comments in
|
|
|
1506 |
keyword/text pairs, one pair per chunk, with no limit on the number
|
|
|
1507 |
of text chunks, and a 2^31 byte limit on their size. While there are
|
|
|
1508 |
suggested keywords, there is no requirement to restrict the use to these
|
|
|
1509 |
strings. It is strongly suggested that keywords and text be sensible
|
|
|
1510 |
to humans (that's the point), so don't use abbreviations. Non-printing
|
|
|
1511 |
symbols are not allowed. See the PNG specification for more details.
|
|
|
1512 |
There is also no requirement to have text after the keyword.
|
|
|
1513 |
|
|
|
1514 |
Keywords should be limited to 79 Latin-1 characters without leading or
|
|
|
1515 |
trailing spaces, but non-consecutive spaces are allowed within the
|
|
|
1516 |
keyword. It is possible to have the same keyword any number of times.
|
|
|
1517 |
The text_ptr is an array of png_text structures, each holding a
|
|
|
1518 |
pointer to a language string, a pointer to a keyword and a pointer to
|
|
|
1519 |
a text string. The text string, language code, and translated
|
|
|
1520 |
keyword may be empty or NULL pointers. The keyword/text
|
|
|
1521 |
pairs are put into the array in the order that they are received.
|
|
|
1522 |
However, some or all of the text chunks may be after the image, so, to
|
|
|
1523 |
make sure you have read all the text chunks, don't mess with these
|
|
|
1524 |
until after you read the stuff after the image. This will be
|
|
|
1525 |
mentioned again below in the discussion that goes with png_read_end().
|
|
|
1526 |
|
|
|
1527 |
.SS Input transformations
|
|
|
1528 |
|
|
|
1529 |
After you've read the header information, you can set up the library
|
|
|
1530 |
to handle any special transformations of the image data. The various
|
|
|
1531 |
ways to transform the data will be described in the order that they
|
|
|
1532 |
should occur. This is important, as some of these change the color
|
|
|
1533 |
type and/or bit depth of the data, and some others only work on
|
|
|
1534 |
certain color types and bit depths. Even though each transformation
|
|
|
1535 |
checks to see if it has data that it can do something with, you should
|
|
|
1536 |
make sure to only enable a transformation if it will be valid for the
|
|
|
1537 |
data. For example, don't swap red and blue on grayscale data.
|
|
|
1538 |
|
|
|
1539 |
The colors used for the background and transparency values should be
|
|
|
1540 |
supplied in the same format/depth as the current image data. They
|
|
|
1541 |
are stored in the same format/depth as the image data in a bKGD or tRNS
|
|
|
1542 |
chunk, so this is what libpng expects for this data. The colors are
|
|
|
1543 |
transformed to keep in sync with the image data when an application
|
|
|
1544 |
calls the png_read_update_info() routine (see below).
|
|
|
1545 |
|
|
|
1546 |
Data will be decoded into the supplied row buffers packed into bytes
|
|
|
1547 |
unless the library has been told to transform it into another format.
|
|
|
1548 |
For example, 4 bit/pixel paletted or grayscale data will be returned
|
|
|
1549 |
2 pixels/byte with the leftmost pixel in the high-order bits of the
|
|
|
1550 |
byte, unless png_set_packing() is called. 8-bit RGB data will be stored
|
|
|
1551 |
in RGB RGB RGB format unless png_set_filler() or png_set_add_alpha()
|
|
|
1552 |
is called to insert filler bytes, either before or after each RGB triplet.
|
|
|
1553 |
16-bit RGB data will be returned RRGGBB RRGGBB, with the most significant
|
|
|
1554 |
byte of the color value first, unless png_set_strip_16() is called to
|
|
|
1555 |
transform it to regular RGB RGB triplets, or png_set_filler() or
|
|
|
1556 |
png_set_add alpha() is called to insert filler bytes, either before or
|
|
|
1557 |
after each RRGGBB triplet. Similarly, 8-bit or 16-bit grayscale data can
|
|
|
1558 |
be modified with
|
|
|
1559 |
png_set_filler(), png_set_add_alpha(), or png_set_strip_16().
|
|
|
1560 |
|
|
|
1561 |
The following code transforms grayscale images of less than 8 to 8 bits,
|
|
|
1562 |
changes paletted images to RGB, and adds a full alpha channel if there is
|
|
|
1563 |
transparency information in a tRNS chunk. This is most useful on
|
|
|
1564 |
grayscale images with bit depths of 2 or 4 or if there is a multiple-image
|
|
|
1565 |
viewing application that wishes to treat all images in the same way.
|
|
|
1566 |
|
|
|
1567 |
if (color_type == PNG_COLOR_TYPE_PALETTE)
|
|
|
1568 |
png_set_palette_to_rgb(png_ptr);
|
|
|
1569 |
|
|
|
1570 |
if (color_type == PNG_COLOR_TYPE_GRAY &&
|
|
|
1571 |
bit_depth < 8) png_set_gray_1_2_4_to_8(png_ptr);
|
|
|
1572 |
|
|
|
1573 |
if (png_get_valid(png_ptr, info_ptr,
|
|
|
1574 |
PNG_INFO_tRNS)) png_set_tRNS_to_alpha(png_ptr);
|
|
|
1575 |
|
|
|
1576 |
These three functions are actually aliases for png_set_expand(), added
|
|
|
1577 |
in libpng version 1.0.4, with the function names expanded to improve code
|
|
|
1578 |
readability. In some future version they may actually do different
|
|
|
1579 |
things.
|
|
|
1580 |
|
|
|
1581 |
PNG can have files with 16 bits per channel. If you only can handle
|
|
|
1582 |
8 bits per channel, this will strip the pixels down to 8 bit.
|
|
|
1583 |
|
|
|
1584 |
if (bit_depth == 16)
|
|
|
1585 |
png_set_strip_16(png_ptr);
|
|
|
1586 |
|
|
|
1587 |
If, for some reason, you don't need the alpha channel on an image,
|
|
|
1588 |
and you want to remove it rather than combining it with the background
|
|
|
1589 |
(but the image author certainly had in mind that you *would* combine
|
|
|
1590 |
it with the background, so that's what you should probably do):
|
|
|
1591 |
|
|
|
1592 |
if (color_type & PNG_COLOR_MASK_ALPHA)
|
|
|
1593 |
png_set_strip_alpha(png_ptr);
|
|
|
1594 |
|
|
|
1595 |
In PNG files, the alpha channel in an image
|
|
|
1596 |
is the level of opacity. If you need the alpha channel in an image to
|
|
|
1597 |
be the level of transparency instead of opacity, you can invert the
|
|
|
1598 |
alpha channel (or the tRNS chunk data) after it's read, so that 0 is
|
|
|
1599 |
fully opaque and 255 (in 8-bit or paletted images) or 65535 (in 16-bit
|
|
|
1600 |
images) is fully transparent, with
|
|
|
1601 |
|
|
|
1602 |
png_set_invert_alpha(png_ptr);
|
|
|
1603 |
|
|
|
1604 |
PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
|
|
|
1605 |
they can, resulting in, for example, 8 pixels per byte for 1 bit
|
|
|
1606 |
files. This code expands to 1 pixel per byte without changing the
|
|
|
1607 |
values of the pixels:
|
|
|
1608 |
|
|
|
1609 |
if (bit_depth < 8)
|
|
|
1610 |
png_set_packing(png_ptr);
|
|
|
1611 |
|
|
|
1612 |
PNG files have possible bit depths of 1, 2, 4, 8, and 16. All pixels
|
|
|
1613 |
stored in a PNG image have been "scaled" or "shifted" up to the next
|
|
|
1614 |
higher possible bit depth (e.g. from 5 bits/sample in the range [0,31] to
|
|
|
1615 |
8 bits/sample in the range [0, 255]). However, it is also possible to
|
|
|
1616 |
convert the PNG pixel data back to the original bit depth of the image.
|
|
|
1617 |
This call reduces the pixels back down to the original bit depth:
|
|
|
1618 |
|
|
|
1619 |
png_color_8p sig_bit;
|
|
|
1620 |
|
|
|
1621 |
if (png_get_sBIT(png_ptr, info_ptr, &sig_bit))
|
|
|
1622 |
png_set_shift(png_ptr, sig_bit);
|
|
|
1623 |
|
|
|
1624 |
PNG files store 3-color pixels in red, green, blue order. This code
|
|
|
1625 |
changes the storage of the pixels to blue, green, red:
|
|
|
1626 |
|
|
|
1627 |
if (color_type == PNG_COLOR_TYPE_RGB ||
|
|
|
1628 |
color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|
|
1629 |
png_set_bgr(png_ptr);
|
|
|
1630 |
|
|
|
1631 |
PNG files store RGB pixels packed into 3 or 6 bytes. This code expands them
|
|
|
1632 |
into 4 or 8 bytes for windowing systems that need them in this format:
|
|
|
1633 |
|
|
|
1634 |
if (color_type == PNG_COLOR_TYPE_RGB)
|
|
|
1635 |
png_set_filler(png_ptr, filler, PNG_FILLER_BEFORE);
|
|
|
1636 |
|
|
|
1637 |
where "filler" is the 8 or 16-bit number to fill with, and the location is
|
|
|
1638 |
either PNG_FILLER_BEFORE or PNG_FILLER_AFTER, depending upon whether
|
|
|
1639 |
you want the filler before the RGB or after. This transformation
|
|
|
1640 |
does not affect images that already have full alpha channels. To add an
|
|
|
1641 |
opaque alpha channel, use filler=0xff or 0xffff and PNG_FILLER_AFTER which
|
|
|
1642 |
will generate RGBA pixels.
|
|
|
1643 |
|
|
|
1644 |
Note that png_set_filler() does not change the color type. If you want
|
|
|
1645 |
to do that, you can add a true alpha channel with
|
|
|
1646 |
|
|
|
1647 |
if (color_type == PNG_COLOR_TYPE_RGB ||
|
|
|
1648 |
color_type == PNG_COLOR_TYPE_GRAY)
|
|
|
1649 |
png_set_add_alpha(png_ptr, filler, PNG_FILLER_AFTER);
|
|
|
1650 |
|
|
|
1651 |
where "filler" contains the alpha value to assign to each pixel.
|
|
|
1652 |
This function was added in libpng-1.2.7.
|
|
|
1653 |
|
|
|
1654 |
If you are reading an image with an alpha channel, and you need the
|
|
|
1655 |
data as ARGB instead of the normal PNG format RGBA:
|
|
|
1656 |
|
|
|
1657 |
if (color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|
|
1658 |
png_set_swap_alpha(png_ptr);
|
|
|
1659 |
|
|
|
1660 |
For some uses, you may want a grayscale image to be represented as
|
|
|
1661 |
RGB. This code will do that conversion:
|
|
|
1662 |
|
|
|
1663 |
if (color_type == PNG_COLOR_TYPE_GRAY ||
|
|
|
1664 |
color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
|
|
|
1665 |
png_set_gray_to_rgb(png_ptr);
|
|
|
1666 |
|
|
|
1667 |
Conversely, you can convert an RGB or RGBA image to grayscale or grayscale
|
|
|
1668 |
with alpha.
|
|
|
1669 |
|
|
|
1670 |
if (color_type == PNG_COLOR_TYPE_RGB ||
|
|
|
1671 |
color_type == PNG_COLOR_TYPE_RGB_ALPHA)
|
|
|
1672 |
png_set_rgb_to_gray_fixed(png_ptr, error_action,
|
|
|
1673 |
int red_weight, int green_weight);
|
|
|
1674 |
|
|
|
1675 |
error_action = 1: silently do the conversion
|
|
|
1676 |
error_action = 2: issue a warning if the original
|
|
|
1677 |
image has any pixel where
|
|
|
1678 |
red != green or red != blue
|
|
|
1679 |
error_action = 3: issue an error and abort the
|
|
|
1680 |
conversion if the original
|
|
|
1681 |
image has any pixel where
|
|
|
1682 |
red != green or red != blue
|
|
|
1683 |
|
|
|
1684 |
red_weight: weight of red component times 100000
|
|
|
1685 |
green_weight: weight of green component times 100000
|
|
|
1686 |
If either weight is negative, default
|
|
|
1687 |
weights (21268, 71514) are used.
|
|
|
1688 |
|
|
|
1689 |
If you have set error_action = 1 or 2, you can
|
|
|
1690 |
later check whether the image really was gray, after processing
|
|
|
1691 |
the image rows, with the png_get_rgb_to_gray_status(png_ptr) function.
|
|
|
1692 |
It will return a png_byte that is zero if the image was gray or
|
|
|
1693 |
1 if there were any non-gray pixels. bKGD and sBIT data
|
|
|
1694 |
will be silently converted to grayscale, using the green channel
|
|
|
1695 |
data, regardless of the error_action setting.
|
|
|
1696 |
|
|
|
1697 |
With red_weight+green_weight<=100000,
|
|
|
1698 |
the normalized graylevel is computed:
|
|
|
1699 |
|
|
|
1700 |
int rw = red_weight * 65536;
|
|
|
1701 |
int gw = green_weight * 65536;
|
|
|
1702 |
int bw = 65536 - (rw + gw);
|
|
|
1703 |
gray = (rw*red + gw*green + bw*blue)/65536;
|
|
|
1704 |
|
|
|
1705 |
The default values approximate those recommended in the Charles
|
|
|
1706 |
Poynton's Color FAQ, <http://www.inforamp.net/~poynton/>
|
|
|
1707 |
Copyright (c) 1998-01-04 Charles Poynton <poynton at inforamp.net>
|
|
|
1708 |
|
|
|
1709 |
Y = 0.212671 * R + 0.715160 * G + 0.072169 * B
|
|
|
1710 |
|
|
|
1711 |
Libpng approximates this with
|
|
|
1712 |
|
|
|
1713 |
Y = 0.21268 * R + 0.7151 * G + 0.07217 * B
|
|
|
1714 |
|
|
|
1715 |
which can be expressed with integers as
|
|
|
1716 |
|
|
|
1717 |
Y = (6969 * R + 23434 * G + 2365 * B)/32768
|
|
|
1718 |
|
|
|
1719 |
The calculation is done in a linear colorspace, if the image gamma
|
|
|
1720 |
is known.
|
|
|
1721 |
|
|
|
1722 |
If you have a grayscale and you are using png_set_expand_depth(),
|
|
|
1723 |
png_set_expand(), or png_set_gray_to_rgb to change to truecolor or to
|
|
|
1724 |
a higher bit-depth, you must either supply the background color as a gray
|
|
|
1725 |
value at the original file bit-depth (need_expand = 1) or else supply the
|
|
|
1726 |
background color as an RGB triplet at the final, expanded bit depth
|
|
|
1727 |
(need_expand = 0). Similarly, if you are reading a paletted image, you
|
|
|
1728 |
must either supply the background color as a palette index (need_expand = 1)
|
|
|
1729 |
or as an RGB triplet that may or may not be in the palette (need_expand = 0).
|
|
|
1730 |
|
|
|
1731 |
png_color_16 my_background;
|
|
|
1732 |
png_color_16p image_background;
|
|
|
1733 |
|
|
|
1734 |
if (png_get_bKGD(png_ptr, info_ptr, &image_background))
|
|
|
1735 |
png_set_background(png_ptr, image_background,
|
|
|
1736 |
PNG_BACKGROUND_GAMMA_FILE, 1, 1.0);
|
|
|
1737 |
else
|
|
|
1738 |
png_set_background(png_ptr, &my_background,
|
|
|
1739 |
PNG_BACKGROUND_GAMMA_SCREEN, 0, 1.0);
|
|
|
1740 |
|
|
|
1741 |
The png_set_background() function tells libpng to composite images
|
|
|
1742 |
with alpha or simple transparency against the supplied background
|
|
|
1743 |
color. If the PNG file contains a bKGD chunk (PNG_INFO_bKGD valid),
|
|
|
1744 |
you may use this color, or supply another color more suitable for
|
|
|
1745 |
the current display (e.g., the background color from a web page). You
|
|
|
1746 |
need to tell libpng whether the color is in the gamma space of the
|
|
|
1747 |
display (PNG_BACKGROUND_GAMMA_SCREEN for colors you supply), the file
|
|
|
1748 |
(PNG_BACKGROUND_GAMMA_FILE for colors from the bKGD chunk), or one
|
|
|
1749 |
that is neither of these gammas (PNG_BACKGROUND_GAMMA_UNIQUE - I don't
|
|
|
1750 |
know why anyone would use this, but it's here).
|
|
|
1751 |
|
|
|
1752 |
To properly display PNG images on any kind of system, the application needs
|
|
|
1753 |
to know what the display gamma is. Ideally, the user will know this, and
|
|
|
1754 |
the application will allow them to set it. One method of allowing the user
|
|
|
1755 |
to set the display gamma separately for each system is to check for a
|
|
|
1756 |
SCREEN_GAMMA or DISPLAY_GAMMA environment variable, which will hopefully be
|
|
|
1757 |
correctly set.
|
|
|
1758 |
|
|
|
1759 |
Note that display_gamma is the overall gamma correction required to produce
|
|
|
1760 |
pleasing results, which depends on the lighting conditions in the surrounding
|
|
|
1761 |
environment. In a dim or brightly lit room, no compensation other than
|
|
|
1762 |
the physical gamma exponent of the monitor is needed, while in a dark room
|
|
|
1763 |
a slightly smaller exponent is better.
|
|
|
1764 |
|
|
|
1765 |
double gamma, screen_gamma;
|
|
|
1766 |
|
|
|
1767 |
if (/* We have a user-defined screen
|
|
|
1768 |
gamma value */)
|
|
|
1769 |
{
|
|
|
1770 |
screen_gamma = user_defined_screen_gamma;
|
|
|
1771 |
}
|
|
|
1772 |
/* One way that applications can share the same
|
|
|
1773 |
screen gamma value */
|
|
|
1774 |
else if ((gamma_str = getenv("SCREEN_GAMMA"))
|
|
|
1775 |
!= NULL)
|
|
|
1776 |
{
|
|
|
1777 |
screen_gamma = (double)atof(gamma_str);
|
|
|
1778 |
}
|
|
|
1779 |
/* If we don't have another value */
|
|
|
1780 |
else
|
|
|
1781 |
{
|
|
|
1782 |
screen_gamma = 2.2; /* A good guess for a
|
|
|
1783 |
PC monitor in a bright office or a dim room */
|
|
|
1784 |
screen_gamma = 2.0; /* A good guess for a
|
|
|
1785 |
PC monitor in a dark room */
|
|
|
1786 |
screen_gamma = 1.7 or 1.0; /* A good
|
|
|
1787 |
guess for Mac systems */
|
|
|
1788 |
}
|
|
|
1789 |
|
|
|
1790 |
The png_set_gamma() function handles gamma transformations of the data.
|
|
|
1791 |
Pass both the file gamma and the current screen_gamma. If the file does
|
|
|
1792 |
not have a gamma value, you can pass one anyway if you have an idea what
|
|
|
1793 |
it is (usually 0.45455 is a good guess for GIF images on PCs). Note
|
|
|
1794 |
that file gammas are inverted from screen gammas. See the discussions
|
|
|
1795 |
on gamma in the PNG specification for an excellent description of what
|
|
|
1796 |
gamma is, and why all applications should support it. It is strongly
|
|
|
1797 |
recommended that PNG viewers support gamma correction.
|
|
|
1798 |
|
|
|
1799 |
if (png_get_gAMA(png_ptr, info_ptr, &gamma))
|
|
|
1800 |
png_set_gamma(png_ptr, screen_gamma, gamma);
|
|
|
1801 |
else
|
|
|
1802 |
png_set_gamma(png_ptr, screen_gamma, 0.45455);
|
|
|
1803 |
|
|
|
1804 |
If you need to reduce an RGB file to a paletted file, or if a paletted
|
|
|
1805 |
file has more entries then will fit on your screen, png_set_dither()
|
|
|
1806 |
will do that. Note that this is a simple match dither that merely
|
|
|
1807 |
finds the closest color available. This should work fairly well with
|
|
|
1808 |
optimized palettes, and fairly badly with linear color cubes. If you
|
|
|
1809 |
pass a palette that is larger then maximum_colors, the file will
|
|
|
1810 |
reduce the number of colors in the palette so it will fit into
|
|
|
1811 |
maximum_colors. If there is a histogram, it will use it to make
|
|
|
1812 |
more intelligent choices when reducing the palette. If there is no
|
|
|
1813 |
histogram, it may not do as good a job.
|
|
|
1814 |
|
|
|
1815 |
if (color_type & PNG_COLOR_MASK_COLOR)
|
|
|
1816 |
{
|
|
|
1817 |
if (png_get_valid(png_ptr, info_ptr,
|
|
|
1818 |
PNG_INFO_PLTE))
|
|
|
1819 |
{
|
|
|
1820 |
png_uint_16p histogram = NULL;
|
|
|
1821 |
|
|
|
1822 |
png_get_hIST(png_ptr, info_ptr,
|
|
|
1823 |
&histogram);
|
|
|
1824 |
png_set_dither(png_ptr, palette, num_palette,
|
|
|
1825 |
max_screen_colors, histogram, 1);
|
|
|
1826 |
}
|
|
|
1827 |
else
|
|
|
1828 |
{
|
|
|
1829 |
png_color std_color_cube[MAX_SCREEN_COLORS] =
|
|
|
1830 |
{ ... colors ... };
|
|
|
1831 |
|
|
|
1832 |
png_set_dither(png_ptr, std_color_cube,
|
|
|
1833 |
MAX_SCREEN_COLORS, MAX_SCREEN_COLORS,
|
|
|
1834 |
NULL,0);
|
|
|
1835 |
}
|
|
|
1836 |
}
|
|
|
1837 |
|
|
|
1838 |
PNG files describe monochrome as black being zero and white being one.
|
|
|
1839 |
The following code will reverse this (make black be one and white be
|
|
|
1840 |
zero):
|
|
|
1841 |
|
|
|
1842 |
if (bit_depth == 1 && color_type == PNG_COLOR_TYPE_GRAY)
|
|
|
1843 |
png_set_invert_mono(png_ptr);
|
|
|
1844 |
|
|
|
1845 |
This function can also be used to invert grayscale and gray-alpha images:
|
|
|
1846 |
|
|
|
1847 |
if (color_type == PNG_COLOR_TYPE_GRAY ||
|
|
|
1848 |
color_type == PNG_COLOR_TYPE_GRAY_ALPHA)
|
|
|
1849 |
png_set_invert_mono(png_ptr);
|
|
|
1850 |
|
|
|
1851 |
PNG files store 16 bit pixels in network byte order (big-endian,
|
|
|
1852 |
ie. most significant bits first). This code changes the storage to the
|
|
|
1853 |
other way (little-endian, i.e. least significant bits first, the
|
|
|
1854 |
way PCs store them):
|
|
|
1855 |
|
|
|
1856 |
if (bit_depth == 16)
|
|
|
1857 |
png_set_swap(png_ptr);
|
|
|
1858 |
|
|
|
1859 |
If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
|
|
|
1860 |
need to change the order the pixels are packed into bytes, you can use:
|
|
|
1861 |
|
|
|
1862 |
if (bit_depth < 8)
|
|
|
1863 |
png_set_packswap(png_ptr);
|
|
|
1864 |
|
|
|
1865 |
Finally, you can write your own transformation function if none of
|
|
|
1866 |
the existing ones meets your needs. This is done by setting a callback
|
|
|
1867 |
with
|
|
|
1868 |
|
|
|
1869 |
png_set_read_user_transform_fn(png_ptr,
|
|
|
1870 |
read_transform_fn);
|
|
|
1871 |
|
|
|
1872 |
You must supply the function
|
|
|
1873 |
|
|
|
1874 |
void read_transform_fn(png_ptr ptr, row_info_ptr
|
|
|
1875 |
row_info, png_bytep data)
|
|
|
1876 |
|
|
|
1877 |
See pngtest.c for a working example. Your function will be called
|
|
|
1878 |
after all of the other transformations have been processed.
|
|
|
1879 |
|
|
|
1880 |
You can also set up a pointer to a user structure for use by your
|
|
|
1881 |
callback function, and you can inform libpng that your transform
|
|
|
1882 |
function will change the number of channels or bit depth with the
|
|
|
1883 |
function
|
|
|
1884 |
|
|
|
1885 |
png_set_user_transform_info(png_ptr, user_ptr,
|
|
|
1886 |
user_depth, user_channels);
|
|
|
1887 |
|
|
|
1888 |
The user's application, not libpng, is responsible for allocating and
|
|
|
1889 |
freeing any memory required for the user structure.
|
|
|
1890 |
|
|
|
1891 |
You can retrieve the pointer via the function
|
|
|
1892 |
png_get_user_transform_ptr(). For example:
|
|
|
1893 |
|
|
|
1894 |
voidp read_user_transform_ptr =
|
|
|
1895 |
png_get_user_transform_ptr(png_ptr);
|
|
|
1896 |
|
|
|
1897 |
The last thing to handle is interlacing; this is covered in detail below,
|
|
|
1898 |
but you must call the function here if you want libpng to handle expansion
|
|
|
1899 |
of the interlaced image.
|
|
|
1900 |
|
|
|
1901 |
number_of_passes = png_set_interlace_handling(png_ptr);
|
|
|
1902 |
|
|
|
1903 |
After setting the transformations, libpng can update your png_info
|
|
|
1904 |
structure to reflect any transformations you've requested with this
|
|
|
1905 |
call. This is most useful to update the info structure's rowbytes
|
|
|
1906 |
field so you can use it to allocate your image memory. This function
|
|
|
1907 |
will also update your palette with the correct screen_gamma and
|
|
|
1908 |
background if these have been given with the calls above.
|
|
|
1909 |
|
|
|
1910 |
png_read_update_info(png_ptr, info_ptr);
|
|
|
1911 |
|
|
|
1912 |
After you call png_read_update_info(), you can allocate any
|
|
|
1913 |
memory you need to hold the image. The row data is simply
|
|
|
1914 |
raw byte data for all forms of images. As the actual allocation
|
|
|
1915 |
varies among applications, no example will be given. If you
|
|
|
1916 |
are allocating one large chunk, you will need to build an
|
|
|
1917 |
array of pointers to each row, as it will be needed for some
|
|
|
1918 |
of the functions below.
|
|
|
1919 |
|
|
|
1920 |
.SS Reading image data
|
|
|
1921 |
|
|
|
1922 |
After you've allocated memory, you can read the image data.
|
|
|
1923 |
The simplest way to do this is in one function call. If you are
|
|
|
1924 |
allocating enough memory to hold the whole image, you can just
|
|
|
1925 |
call png_read_image() and libpng will read in all the image data
|
|
|
1926 |
and put it in the memory area supplied. You will need to pass in
|
|
|
1927 |
an array of pointers to each row.
|
|
|
1928 |
|
|
|
1929 |
This function automatically handles interlacing, so you don't need
|
|
|
1930 |
to call png_set_interlace_handling() or call this function multiple
|
|
|
1931 |
times, or any of that other stuff necessary with png_read_rows().
|
|
|
1932 |
|
|
|
1933 |
png_read_image(png_ptr, row_pointers);
|
|
|
1934 |
|
|
|
1935 |
where row_pointers is:
|
|
|
1936 |
|
|
|
1937 |
png_bytep row_pointers[height];
|
|
|
1938 |
|
|
|
1939 |
You can point to void or char or whatever you use for pixels.
|
|
|
1940 |
|
|
|
1941 |
If you don't want to read in the whole image at once, you can
|
|
|
1942 |
use png_read_rows() instead. If there is no interlacing (check
|
|
|
1943 |
interlace_type == PNG_INTERLACE_NONE), this is simple:
|
|
|
1944 |
|
|
|
1945 |
png_read_rows(png_ptr, row_pointers, NULL,
|
|
|
1946 |
number_of_rows);
|
|
|
1947 |
|
|
|
1948 |
where row_pointers is the same as in the png_read_image() call.
|
|
|
1949 |
|
|
|
1950 |
If you are doing this just one row at a time, you can do this with
|
|
|
1951 |
a single row_pointer instead of an array of row_pointers:
|
|
|
1952 |
|
|
|
1953 |
png_bytep row_pointer = row;
|
|
|
1954 |
png_read_row(png_ptr, row_pointer, NULL);
|
|
|
1955 |
|
|
|
1956 |
If the file is interlaced (interlace_type != 0 in the IHDR chunk), things
|
|
|
1957 |
get somewhat harder. The only current (PNG Specification version 1.2)
|
|
|
1958 |
interlacing type for PNG is (interlace_type == PNG_INTERLACE_ADAM7)
|
|
|
1959 |
is a somewhat complicated 2D interlace scheme, known as Adam7, that
|
|
|
1960 |
breaks down an image into seven smaller images of varying size, based
|
|
|
1961 |
on an 8x8 grid.
|
|
|
1962 |
|
|
|
1963 |
libpng can fill out those images or it can give them to you "as is".
|
|
|
1964 |
If you want them filled out, there are two ways to do that. The one
|
|
|
1965 |
mentioned in the PNG specification is to expand each pixel to cover
|
|
|
1966 |
those pixels that have not been read yet (the "rectangle" method).
|
|
|
1967 |
This results in a blocky image for the first pass, which gradually
|
|
|
1968 |
smooths out as more pixels are read. The other method is the "sparkle"
|
|
|
1969 |
method, where pixels are drawn only in their final locations, with the
|
|
|
1970 |
rest of the image remaining whatever colors they were initialized to
|
|
|
1971 |
before the start of the read. The first method usually looks better,
|
|
|
1972 |
but tends to be slower, as there are more pixels to put in the rows.
|
|
|
1973 |
|
|
|
1974 |
If you don't want libpng to handle the interlacing details, just call
|
|
|
1975 |
png_read_rows() seven times to read in all seven images. Each of the
|
|
|
1976 |
images is a valid image by itself, or they can all be combined on an
|
|
|
1977 |
8x8 grid to form a single image (although if you intend to combine them
|
|
|
1978 |
you would be far better off using the libpng interlace handling).
|
|
|
1979 |
|
|
|
1980 |
The first pass will return an image 1/8 as wide as the entire image
|
|
|
1981 |
(every 8th column starting in column 0) and 1/8 as high as the original
|
|
|
1982 |
(every 8th row starting in row 0), the second will be 1/8 as wide
|
|
|
1983 |
(starting in column 4) and 1/8 as high (also starting in row 0). The
|
|
|
1984 |
third pass will be 1/4 as wide (every 4th pixel starting in column 0) and
|
|
|
1985 |
1/8 as high (every 8th row starting in row 4), and the fourth pass will
|
|
|
1986 |
be 1/4 as wide and 1/4 as high (every 4th column starting in column 2,
|
|
|
1987 |
and every 4th row starting in row 0). The fifth pass will return an
|
|
|
1988 |
image 1/2 as wide, and 1/4 as high (starting at column 0 and row 2),
|
|
|
1989 |
while the sixth pass will be 1/2 as wide and 1/2 as high as the original
|
|
|
1990 |
(starting in column 1 and row 0). The seventh and final pass will be as
|
|
|
1991 |
wide as the original, and 1/2 as high, containing all of the odd
|
|
|
1992 |
numbered scanlines. Phew!
|
|
|
1993 |
|
|
|
1994 |
If you want libpng to expand the images, call this before calling
|
|
|
1995 |
png_start_read_image() or png_read_update_info():
|
|
|
1996 |
|
|
|
1997 |
if (interlace_type == PNG_INTERLACE_ADAM7)
|
|
|
1998 |
number_of_passes
|
|
|
1999 |
= png_set_interlace_handling(png_ptr);
|
|
|
2000 |
|
|
|
2001 |
This will return the number of passes needed. Currently, this
|
|
|
2002 |
is seven, but may change if another interlace type is added.
|
|
|
2003 |
This function can be called even if the file is not interlaced,
|
|
|
2004 |
where it will return one pass.
|
|
|
2005 |
|
|
|
2006 |
If you are not going to display the image after each pass, but are
|
|
|
2007 |
going to wait until the entire image is read in, use the sparkle
|
|
|
2008 |
effect. This effect is faster and the end result of either method
|
|
|
2009 |
is exactly the same. If you are planning on displaying the image
|
|
|
2010 |
after each pass, the "rectangle" effect is generally considered the
|
|
|
2011 |
better looking one.
|
|
|
2012 |
|
|
|
2013 |
If you only want the "sparkle" effect, just call png_read_rows() as
|
|
|
2014 |
normal, with the third parameter NULL. Make sure you make pass over
|
|
|
2015 |
the image number_of_passes times, and you don't change the data in the
|
|
|
2016 |
rows between calls. You can change the locations of the data, just
|
|
|
2017 |
not the data. Each pass only writes the pixels appropriate for that
|
|
|
2018 |
pass, and assumes the data from previous passes is still valid.
|
|
|
2019 |
|
|
|
2020 |
png_read_rows(png_ptr, row_pointers, NULL,
|
|
|
2021 |
number_of_rows);
|
|
|
2022 |
|
|
|
2023 |
If you only want the first effect (the rectangles), do the same as
|
|
|
2024 |
before except pass the row buffer in the third parameter, and leave
|
|
|
2025 |
the second parameter NULL.
|
|
|
2026 |
|
|
|
2027 |
png_read_rows(png_ptr, NULL, row_pointers,
|
|
|
2028 |
number_of_rows);
|
|
|
2029 |
|
|
|
2030 |
.SS Finishing a sequential read
|
|
|
2031 |
|
|
|
2032 |
After you are finished reading the image through either the high- or
|
|
|
2033 |
low-level interfaces, you can finish reading the file. If you are
|
|
|
2034 |
interested in comments or time, which may be stored either before or
|
|
|
2035 |
after the image data, you should pass the separate png_info struct if
|
|
|
2036 |
you want to keep the comments from before and after the image
|
|
|
2037 |
separate. If you are not interested, you can pass NULL.
|
|
|
2038 |
|
|
|
2039 |
png_read_end(png_ptr, end_info);
|
|
|
2040 |
|
|
|
2041 |
When you are done, you can free all memory allocated by libpng like this:
|
|
|
2042 |
|
|
|
2043 |
png_destroy_read_struct(&png_ptr, &info_ptr,
|
|
|
2044 |
&end_info);
|
|
|
2045 |
|
|
|
2046 |
It is also possible to individually free the info_ptr members that
|
|
|
2047 |
point to libpng-allocated storage with the following function:
|
|
|
2048 |
|
|
|
2049 |
png_free_data(png_ptr, info_ptr, mask, seq)
|
|
|
2050 |
mask - identifies data to be freed, a mask
|
|
|
2051 |
containing the logical OR of one or
|
|
|
2052 |
more of
|
|
|
2053 |
PNG_FREE_PLTE, PNG_FREE_TRNS,
|
|
|
2054 |
PNG_FREE_HIST, PNG_FREE_ICCP,
|
|
|
2055 |
PNG_FREE_PCAL, PNG_FREE_ROWS,
|
|
|
2056 |
PNG_FREE_SCAL, PNG_FREE_SPLT,
|
|
|
2057 |
PNG_FREE_TEXT, PNG_FREE_UNKN,
|
|
|
2058 |
or simply PNG_FREE_ALL
|
|
|
2059 |
seq - sequence number of item to be freed
|
|
|
2060 |
(-1 for all items)
|
|
|
2061 |
|
|
|
2062 |
This function may be safely called when the relevant storage has
|
|
|
2063 |
already been freed, or has not yet been allocated, or was allocated
|
|
|
2064 |
by the user and not by libpng, and will in those
|
|
|
2065 |
cases do nothing. The "seq" parameter is ignored if only one item
|
|
|
2066 |
of the selected data type, such as PLTE, is allowed. If "seq" is not
|
|
|
2067 |
-1, and multiple items are allowed for the data type identified in
|
|
|
2068 |
the mask, such as text or sPLT, only the n'th item in the structure
|
|
|
2069 |
is freed, where n is "seq".
|
|
|
2070 |
|
|
|
2071 |
The default behavior is only to free data that was allocated internally
|
|
|
2072 |
by libpng. This can be changed, so that libpng will not free the data,
|
|
|
2073 |
or so that it will free data that was allocated by the user with png_malloc()
|
|
|
2074 |
or png_zalloc() and passed in via a png_set_*() function, with
|
|
|
2075 |
|
|
|
2076 |
png_data_freer(png_ptr, info_ptr, freer, mask)
|
|
|
2077 |
mask - which data elements are affected
|
|
|
2078 |
same choices as in png_free_data()
|
|
|
2079 |
freer - one of
|
|
|
2080 |
PNG_DESTROY_WILL_FREE_DATA
|
|
|
2081 |
PNG_SET_WILL_FREE_DATA
|
|
|
2082 |
PNG_USER_WILL_FREE_DATA
|
|
|
2083 |
|
|
|
2084 |
This function only affects data that has already been allocated.
|
|
|
2085 |
You can call this function after reading the PNG data but before calling
|
|
|
2086 |
any png_set_*() functions, to control whether the user or the png_set_*()
|
|
|
2087 |
function is responsible for freeing any existing data that might be present,
|
|
|
2088 |
and again after the png_set_*() functions to control whether the user
|
|
|
2089 |
or png_destroy_*() is supposed to free the data. When the user assumes
|
|
|
2090 |
responsibility for libpng-allocated data, the application must use
|
|
|
2091 |
png_free() to free it, and when the user transfers responsibility to libpng
|
|
|
2092 |
for data that the user has allocated, the user must have used png_malloc()
|
|
|
2093 |
or png_zalloc() to allocate it.
|
|
|
2094 |
|
|
|
2095 |
If you allocated your row_pointers in a single block, as suggested above in
|
|
|
2096 |
the description of the high level read interface, you must not transfer
|
|
|
2097 |
responsibility for freeing it to the png_set_rows or png_read_destroy function,
|
|
|
2098 |
because they would also try to free the individual row_pointers[i].
|
|
|
2099 |
|
|
|
2100 |
If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
|
|
|
2101 |
separately, do not transfer responsibility for freeing text_ptr to libpng,
|
|
|
2102 |
because when libpng fills a png_text structure it combines these members with
|
|
|
2103 |
the key member, and png_free_data() will free only text_ptr.key. Similarly,
|
|
|
2104 |
if you transfer responsibility for free'ing text_ptr from libpng to your
|
|
|
2105 |
application, your application must not separately free those members.
|
|
|
2106 |
|
|
|
2107 |
The png_free_data() function will turn off the "valid" flag for anything
|
|
|
2108 |
it frees. If you need to turn the flag off for a chunk that was freed by your
|
|
|
2109 |
application instead of by libpng, you can use
|
|
|
2110 |
|
|
|
2111 |
png_set_invalid(png_ptr, info_ptr, mask);
|
|
|
2112 |
mask - identifies the chunks to be made invalid,
|
|
|
2113 |
containing the logical OR of one or
|
|
|
2114 |
more of
|
|
|
2115 |
PNG_INFO_gAMA, PNG_INFO_sBIT,
|
|
|
2116 |
PNG_INFO_cHRM, PNG_INFO_PLTE,
|
|
|
2117 |
PNG_INFO_tRNS, PNG_INFO_bKGD,
|
|
|
2118 |
PNG_INFO_hIST, PNG_INFO_pHYs,
|
|
|
2119 |
PNG_INFO_oFFs, PNG_INFO_tIME,
|
|
|
2120 |
PNG_INFO_pCAL, PNG_INFO_sRGB,
|
|
|
2121 |
PNG_INFO_iCCP, PNG_INFO_sPLT,
|
|
|
2122 |
PNG_INFO_sCAL, PNG_INFO_IDAT
|
|
|
2123 |
|
|
|
2124 |
For a more compact example of reading a PNG image, see the file example.c.
|
|
|
2125 |
|
|
|
2126 |
.SS Reading PNG files progressively
|
|
|
2127 |
|
|
|
2128 |
The progressive reader is slightly different then the non-progressive
|
|
|
2129 |
reader. Instead of calling png_read_info(), png_read_rows(), and
|
|
|
2130 |
png_read_end(), you make one call to png_process_data(), which calls
|
|
|
2131 |
callbacks when it has the info, a row, or the end of the image. You
|
|
|
2132 |
set up these callbacks with png_set_progressive_read_fn(). You don't
|
|
|
2133 |
have to worry about the input/output functions of libpng, as you are
|
|
|
2134 |
giving the library the data directly in png_process_data(). I will
|
|
|
2135 |
assume that you have read the section on reading PNG files above,
|
|
|
2136 |
so I will only highlight the differences (although I will show
|
|
|
2137 |
all of the code).
|
|
|
2138 |
|
|
|
2139 |
png_structp png_ptr;
|
|
|
2140 |
png_infop info_ptr;
|
|
|
2141 |
|
|
|
2142 |
/* An example code fragment of how you would
|
|
|
2143 |
initialize the progressive reader in your
|
|
|
2144 |
application. */
|
|
|
2145 |
int
|
|
|
2146 |
initialize_png_reader()
|
|
|
2147 |
{
|
|
|
2148 |
png_ptr = png_create_read_struct
|
|
|
2149 |
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
|
2150 |
user_error_fn, user_warning_fn);
|
|
|
2151 |
if (!png_ptr)
|
|
|
2152 |
return (ERROR);
|
|
|
2153 |
info_ptr = png_create_info_struct(png_ptr);
|
|
|
2154 |
if (!info_ptr)
|
|
|
2155 |
{
|
|
|
2156 |
png_destroy_read_struct(&png_ptr, (png_infopp)NULL,
|
|
|
2157 |
(png_infopp)NULL);
|
|
|
2158 |
return (ERROR);
|
|
|
2159 |
}
|
|
|
2160 |
|
|
|
2161 |
if (setjmp(png_jmpbuf(png_ptr)))
|
|
|
2162 |
{
|
|
|
2163 |
png_destroy_read_struct(&png_ptr, &info_ptr,
|
|
|
2164 |
(png_infopp)NULL);
|
|
|
2165 |
return (ERROR);
|
|
|
2166 |
}
|
|
|
2167 |
|
|
|
2168 |
/* This one's new. You can provide functions
|
|
|
2169 |
to be called when the header info is valid,
|
|
|
2170 |
when each row is completed, and when the image
|
|
|
2171 |
is finished. If you aren't using all functions,
|
|
|
2172 |
you can specify NULL parameters. Even when all
|
|
|
2173 |
three functions are NULL, you need to call
|
|
|
2174 |
png_set_progressive_read_fn(). You can use
|
|
|
2175 |
any struct as the user_ptr (cast to a void pointer
|
|
|
2176 |
for the function call), and retrieve the pointer
|
|
|
2177 |
from inside the callbacks using the function
|
|
|
2178 |
|
|
|
2179 |
png_get_progressive_ptr(png_ptr);
|
|
|
2180 |
|
|
|
2181 |
which will return a void pointer, which you have
|
|
|
2182 |
to cast appropriately.
|
|
|
2183 |
*/
|
|
|
2184 |
png_set_progressive_read_fn(png_ptr, (void *)user_ptr,
|
|
|
2185 |
info_callback, row_callback, end_callback);
|
|
|
2186 |
|
|
|
2187 |
return 0;
|
|
|
2188 |
}
|
|
|
2189 |
|
|
|
2190 |
/* A code fragment that you call as you receive blocks
|
|
|
2191 |
of data */
|
|
|
2192 |
int
|
|
|
2193 |
process_data(png_bytep buffer, png_uint_32 length)
|
|
|
2194 |
{
|
|
|
2195 |
if (setjmp(png_jmpbuf(png_ptr)))
|
|
|
2196 |
{
|
|
|
2197 |
png_destroy_read_struct(&png_ptr, &info_ptr,
|
|
|
2198 |
(png_infopp)NULL);
|
|
|
2199 |
return (ERROR);
|
|
|
2200 |
}
|
|
|
2201 |
|
|
|
2202 |
/* This one's new also. Simply give it a chunk
|
|
|
2203 |
of data from the file stream (in order, of
|
|
|
2204 |
course). On machines with segmented memory
|
|
|
2205 |
models machines, don't give it any more than
|
|
|
2206 |
64K. The library seems to run fine with sizes
|
|
|
2207 |
of 4K. Although you can give it much less if
|
|
|
2208 |
necessary (I assume you can give it chunks of
|
|
|
2209 |
1 byte, I haven't tried less then 256 bytes
|
|
|
2210 |
yet). When this function returns, you may
|
|
|
2211 |
want to display any rows that were generated
|
|
|
2212 |
in the row callback if you don't already do
|
|
|
2213 |
so there.
|
|
|
2214 |
*/
|
|
|
2215 |
png_process_data(png_ptr, info_ptr, buffer, length);
|
|
|
2216 |
return 0;
|
|
|
2217 |
}
|
|
|
2218 |
|
|
|
2219 |
/* This function is called (as set by
|
|
|
2220 |
png_set_progressive_read_fn() above) when enough data
|
|
|
2221 |
has been supplied so all of the header has been
|
|
|
2222 |
read.
|
|
|
2223 |
*/
|
|
|
2224 |
void
|
|
|
2225 |
info_callback(png_structp png_ptr, png_infop info)
|
|
|
2226 |
{
|
|
|
2227 |
/* Do any setup here, including setting any of
|
|
|
2228 |
the transformations mentioned in the Reading
|
|
|
2229 |
PNG files section. For now, you _must_ call
|
|
|
2230 |
either png_start_read_image() or
|
|
|
2231 |
png_read_update_info() after all the
|
|
|
2232 |
transformations are set (even if you don't set
|
|
|
2233 |
any). You may start getting rows before
|
|
|
2234 |
png_process_data() returns, so this is your
|
|
|
2235 |
last chance to prepare for that.
|
|
|
2236 |
*/
|
|
|
2237 |
}
|
|
|
2238 |
|
|
|
2239 |
/* This function is called when each row of image
|
|
|
2240 |
data is complete */
|
|
|
2241 |
void
|
|
|
2242 |
row_callback(png_structp png_ptr, png_bytep new_row,
|
|
|
2243 |
png_uint_32 row_num, int pass)
|
|
|
2244 |
{
|
|
|
2245 |
/* If the image is interlaced, and you turned
|
|
|
2246 |
on the interlace handler, this function will
|
|
|
2247 |
be called for every row in every pass. Some
|
|
|
2248 |
of these rows will not be changed from the
|
|
|
2249 |
previous pass. When the row is not changed,
|
|
|
2250 |
the new_row variable will be NULL. The rows
|
|
|
2251 |
and passes are called in order, so you don't
|
|
|
2252 |
really need the row_num and pass, but I'm
|
|
|
2253 |
supplying them because it may make your life
|
|
|
2254 |
easier.
|
|
|
2255 |
|
|
|
2256 |
For the non-NULL rows of interlaced images,
|
|
|
2257 |
you must call png_progressive_combine_row()
|
|
|
2258 |
passing in the row and the old row. You can
|
|
|
2259 |
call this function for NULL rows (it will just
|
|
|
2260 |
return) and for non-interlaced images (it just
|
|
|
2261 |
does the memcpy for you) if it will make the
|
|
|
2262 |
code easier. Thus, you can just do this for
|
|
|
2263 |
all cases:
|
|
|
2264 |
*/
|
|
|
2265 |
|
|
|
2266 |
png_progressive_combine_row(png_ptr, old_row,
|
|
|
2267 |
new_row);
|
|
|
2268 |
|
|
|
2269 |
/* where old_row is what was displayed for
|
|
|
2270 |
previously for the row. Note that the first
|
|
|
2271 |
pass (pass == 0, really) will completely cover
|
|
|
2272 |
the old row, so the rows do not have to be
|
|
|
2273 |
initialized. After the first pass (and only
|
|
|
2274 |
for interlaced images), you will have to pass
|
|
|
2275 |
the current row, and the function will combine
|
|
|
2276 |
the old row and the new row.
|
|
|
2277 |
*/
|
|
|
2278 |
}
|
|
|
2279 |
|
|
|
2280 |
void
|
|
|
2281 |
end_callback(png_structp png_ptr, png_infop info)
|
|
|
2282 |
{
|
|
|
2283 |
/* This function is called after the whole image
|
|
|
2284 |
has been read, including any chunks after the
|
|
|
2285 |
image (up to and including the IEND). You
|
|
|
2286 |
will usually have the same info chunk as you
|
|
|
2287 |
had in the header, although some data may have
|
|
|
2288 |
been added to the comments and time fields.
|
|
|
2289 |
|
|
|
2290 |
Most people won't do much here, perhaps setting
|
|
|
2291 |
a flag that marks the image as finished.
|
|
|
2292 |
*/
|
|
|
2293 |
}
|
|
|
2294 |
|
|
|
2295 |
|
|
|
2296 |
|
|
|
2297 |
.SH IV. Writing
|
|
|
2298 |
|
|
|
2299 |
Much of this is very similar to reading. However, everything of
|
|
|
2300 |
importance is repeated here, so you won't have to constantly look
|
|
|
2301 |
back up in the reading section to understand writing.
|
|
|
2302 |
|
|
|
2303 |
.SS Setup
|
|
|
2304 |
|
|
|
2305 |
You will want to do the I/O initialization before you get into libpng,
|
|
|
2306 |
so if it doesn't work, you don't have anything to undo. If you are not
|
|
|
2307 |
using the standard I/O functions, you will need to replace them with
|
|
|
2308 |
custom writing functions. See the discussion under Customizing libpng.
|
|
|
2309 |
|
|
|
2310 |
FILE *fp = fopen(file_name, "wb");
|
|
|
2311 |
if (!fp)
|
|
|
2312 |
{
|
|
|
2313 |
return (ERROR);
|
|
|
2314 |
}
|
|
|
2315 |
|
|
|
2316 |
Next, png_struct and png_info need to be allocated and initialized.
|
|
|
2317 |
As these can be both relatively large, you may not want to store these
|
|
|
2318 |
on the stack, unless you have stack space to spare. Of course, you
|
|
|
2319 |
will want to check if they return NULL. If you are also reading,
|
|
|
2320 |
you won't want to name your read structure and your write structure
|
|
|
2321 |
both "png_ptr"; you can call them anything you like, such as
|
|
|
2322 |
"read_ptr" and "write_ptr". Look at pngtest.c, for example.
|
|
|
2323 |
|
|
|
2324 |
png_structp png_ptr = png_create_write_struct
|
|
|
2325 |
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
|
2326 |
user_error_fn, user_warning_fn);
|
|
|
2327 |
if (!png_ptr)
|
|
|
2328 |
return (ERROR);
|
|
|
2329 |
|
|
|
2330 |
png_infop info_ptr = png_create_info_struct(png_ptr);
|
|
|
2331 |
if (!info_ptr)
|
|
|
2332 |
{
|
|
|
2333 |
png_destroy_write_struct(&png_ptr,
|
|
|
2334 |
(png_infopp)NULL);
|
|
|
2335 |
return (ERROR);
|
|
|
2336 |
}
|
|
|
2337 |
|
|
|
2338 |
If you want to use your own memory allocation routines,
|
|
|
2339 |
define PNG_USER_MEM_SUPPORTED and use
|
|
|
2340 |
png_create_write_struct_2() instead of png_create_write_struct():
|
|
|
2341 |
|
|
|
2342 |
png_structp png_ptr = png_create_write_struct_2
|
|
|
2343 |
(PNG_LIBPNG_VER_STRING, (png_voidp)user_error_ptr,
|
|
|
2344 |
user_error_fn, user_warning_fn, (png_voidp)
|
|
|
2345 |
user_mem_ptr, user_malloc_fn, user_free_fn);
|
|
|
2346 |
|
|
|
2347 |
After you have these structures, you will need to set up the
|
|
|
2348 |
error handling. When libpng encounters an error, it expects to
|
|
|
2349 |
longjmp() back to your routine. Therefore, you will need to call
|
|
|
2350 |
setjmp() and pass the png_jmpbuf(png_ptr). If you
|
|
|
2351 |
write the file from different routines, you will need to update
|
|
|
2352 |
the png_jmpbuf(png_ptr) every time you enter a new routine that will
|
|
|
2353 |
call a png_*() function. See your documentation of setjmp/longjmp
|
|
|
2354 |
for your compiler for more information on setjmp/longjmp. See
|
|
|
2355 |
the discussion on libpng error handling in the Customizing Libpng
|
|
|
2356 |
section below for more information on the libpng error handling.
|
|
|
2357 |
|
|
|
2358 |
if (setjmp(png_jmpbuf(png_ptr)))
|
|
|
2359 |
{
|
|
|
2360 |
png_destroy_write_struct(&png_ptr, &info_ptr);
|
|
|
2361 |
fclose(fp);
|
|
|
2362 |
return (ERROR);
|
|
|
2363 |
}
|
|
|
2364 |
...
|
|
|
2365 |
return;
|
|
|
2366 |
|
|
|
2367 |
If you would rather avoid the complexity of setjmp/longjmp issues,
|
|
|
2368 |
you can compile libpng with PNG_SETJMP_NOT_SUPPORTED, in which case
|
|
|
2369 |
errors will result in a call to PNG_ABORT() which defaults to abort().
|
|
|
2370 |
|
|
|
2371 |
Now you need to set up the output code. The default for libpng is to
|
|
|
2372 |
use the C function fwrite(). If you use this, you will need to pass a
|
|
|
2373 |
valid FILE * in the function png_init_io(). Be sure that the file is
|
|
|
2374 |
opened in binary mode. Again, if you wish to handle writing data in
|
|
|
2375 |
another way, see the discussion on libpng I/O handling in the Customizing
|
|
|
2376 |
Libpng section below.
|
|
|
2377 |
|
|
|
2378 |
png_init_io(png_ptr, fp);
|
|
|
2379 |
|
|
|
2380 |
.SS Write callbacks
|
|
|
2381 |
|
|
|
2382 |
At this point, you can set up a callback function that will be
|
|
|
2383 |
called after each row has been written, which you can use to control
|
|
|
2384 |
a progress meter or the like. It's demonstrated in pngtest.c.
|
|
|
2385 |
You must supply a function
|
|
|
2386 |
|
|
|
2387 |
void write_row_callback(png_ptr, png_uint_32 row,
|
|
|
2388 |
int pass);
|
|
|
2389 |
{
|
|
|
2390 |
/* put your code here */
|
|
|
2391 |
}
|
|
|
2392 |
|
|
|
2393 |
(You can give it another name that you like instead of "write_row_callback")
|
|
|
2394 |
|
|
|
2395 |
To inform libpng about your function, use
|
|
|
2396 |
|
|
|
2397 |
png_set_write_status_fn(png_ptr, write_row_callback);
|
|
|
2398 |
|
|
|
2399 |
You now have the option of modifying how the compression library will
|
|
|
2400 |
run. The following functions are mainly for testing, but may be useful
|
|
|
2401 |
in some cases, like if you need to write PNG files extremely fast and
|
|
|
2402 |
are willing to give up some compression, or if you want to get the
|
|
|
2403 |
maximum possible compression at the expense of slower writing. If you
|
|
|
2404 |
have no special needs in this area, let the library do what it wants by
|
|
|
2405 |
not calling this function at all, as it has been tuned to deliver a good
|
|
|
2406 |
speed/compression ratio. The second parameter to png_set_filter() is
|
|
|
2407 |
the filter method, for which the only valid values are 0 (as of the
|
|
|
2408 |
July 1999 PNG specification, version 1.2) or 64 (if you are writing
|
|
|
2409 |
a PNG datastream that is to be embedded in a MNG datastream). The third
|
|
|
2410 |
parameter is a flag that indicates which filter type(s) are to be tested
|
|
|
2411 |
for each scanline. See the PNG specification for details on the specific filter
|
|
|
2412 |
types.
|
|
|
2413 |
|
|
|
2414 |
|
|
|
2415 |
/* turn on or off filtering, and/or choose
|
|
|
2416 |
specific filters. You can use either a single
|
|
|
2417 |
PNG_FILTER_VALUE_NAME or the logical OR of one
|
|
|
2418 |
or more PNG_FILTER_NAME masks. */
|
|
|
2419 |
png_set_filter(png_ptr, 0,
|
|
|
2420 |
PNG_FILTER_NONE | PNG_FILTER_VALUE_NONE |
|
|
|
2421 |
PNG_FILTER_SUB | PNG_FILTER_VALUE_SUB |
|
|
|
2422 |
PNG_FILTER_UP | PNG_FILTER_VALUE_UP |
|
|
|
2423 |
PNG_FILTER_AVE | PNG_FILTER_VALUE_AVE |
|
|
|
2424 |
PNG_FILTER_PAETH | PNG_FILTER_VALUE_PAETH|
|
|
|
2425 |
PNG_ALL_FILTERS);
|
|
|
2426 |
|
|
|
2427 |
If an application
|
|
|
2428 |
wants to start and stop using particular filters during compression,
|
|
|
2429 |
it should start out with all of the filters (to ensure that the previous
|
|
|
2430 |
row of pixels will be stored in case it's needed later), and then add
|
|
|
2431 |
and remove them after the start of compression.
|
|
|
2432 |
|
|
|
2433 |
If you are writing a PNG datastream that is to be embedded in a MNG
|
|
|
2434 |
datastream, the second parameter can be either 0 or 64.
|
|
|
2435 |
|
|
|
2436 |
The png_set_compression_*() functions interface to the zlib compression
|
|
|
2437 |
library, and should mostly be ignored unless you really know what you are
|
|
|
2438 |
doing. The only generally useful call is png_set_compression_level()
|
|
|
2439 |
which changes how much time zlib spends on trying to compress the image
|
|
|
2440 |
data. See the Compression Library (zlib.h and algorithm.txt, distributed
|
|
|
2441 |
with zlib) for details on the compression levels.
|
|
|
2442 |
|
|
|
2443 |
/* set the zlib compression level */
|
|
|
2444 |
png_set_compression_level(png_ptr,
|
|
|
2445 |
Z_BEST_COMPRESSION);
|
|
|
2446 |
|
|
|
2447 |
/* set other zlib parameters */
|
|
|
2448 |
png_set_compression_mem_level(png_ptr, 8);
|
|
|
2449 |
png_set_compression_strategy(png_ptr,
|
|
|
2450 |
Z_DEFAULT_STRATEGY);
|
|
|
2451 |
png_set_compression_window_bits(png_ptr, 15);
|
|
|
2452 |
png_set_compression_method(png_ptr, 8);
|
|
|
2453 |
png_set_compression_buffer_size(png_ptr, 8192)
|
|
|
2454 |
|
|
|
2455 |
extern PNG_EXPORT(void,png_set_zbuf_size)
|
|
|
2456 |
|
|
|
2457 |
.SS Setting the contents of info for output
|
|
|
2458 |
|
|
|
2459 |
You now need to fill in the png_info structure with all the data you
|
|
|
2460 |
wish to write before the actual image. Note that the only thing you
|
|
|
2461 |
are allowed to write after the image is the text chunks and the time
|
|
|
2462 |
chunk (as of PNG Specification 1.2, anyway). See png_write_end() and
|
|
|
2463 |
the latest PNG specification for more information on that. If you
|
|
|
2464 |
wish to write them before the image, fill them in now, and flag that
|
|
|
2465 |
data as being valid. If you want to wait until after the data, don't
|
|
|
2466 |
fill them until png_write_end(). For all the fields in png_info and
|
|
|
2467 |
their data types, see png.h. For explanations of what the fields
|
|
|
2468 |
contain, see the PNG specification.
|
|
|
2469 |
|
|
|
2470 |
Some of the more important parts of the png_info are:
|
|
|
2471 |
|
|
|
2472 |
png_set_IHDR(png_ptr, info_ptr, width, height,
|
|
|
2473 |
bit_depth, color_type, interlace_type,
|
|
|
2474 |
compression_type, filter_method)
|
|
|
2475 |
width - holds the width of the image
|
|
|
2476 |
in pixels (up to 2^31).
|
|
|
2477 |
height - holds the height of the image
|
|
|
2478 |
in pixels (up to 2^31).
|
|
|
2479 |
bit_depth - holds the bit depth of one of the
|
|
|
2480 |
image channels.
|
|
|
2481 |
(valid values are 1, 2, 4, 8, 16
|
|
|
2482 |
and depend also on the
|
|
|
2483 |
color_type. See also significant
|
|
|
2484 |
bits (sBIT) below).
|
|
|
2485 |
color_type - describes which color/alpha
|
|
|
2486 |
channels are present.
|
|
|
2487 |
PNG_COLOR_TYPE_GRAY
|
|
|
2488 |
(bit depths 1, 2, 4, 8, 16)
|
|
|
2489 |
PNG_COLOR_TYPE_GRAY_ALPHA
|
|
|
2490 |
(bit depths 8, 16)
|
|
|
2491 |
PNG_COLOR_TYPE_PALETTE
|
|
|
2492 |
(bit depths 1, 2, 4, 8)
|
|
|
2493 |
PNG_COLOR_TYPE_RGB
|
|
|
2494 |
(bit_depths 8, 16)
|
|
|
2495 |
PNG_COLOR_TYPE_RGB_ALPHA
|
|
|
2496 |
(bit_depths 8, 16)
|
|
|
2497 |
|
|
|
2498 |
PNG_COLOR_MASK_PALETTE
|
|
|
2499 |
PNG_COLOR_MASK_COLOR
|
|
|
2500 |
PNG_COLOR_MASK_ALPHA
|
|
|
2501 |
|
|
|
2502 |
interlace_type - PNG_INTERLACE_NONE or
|
|
|
2503 |
PNG_INTERLACE_ADAM7
|
|
|
2504 |
compression_type - (must be
|
|
|
2505 |
PNG_COMPRESSION_TYPE_DEFAULT)
|
|
|
2506 |
filter_method - (must be PNG_FILTER_TYPE_DEFAULT
|
|
|
2507 |
or, if you are writing a PNG to
|
|
|
2508 |
be embedded in a MNG datastream,
|
|
|
2509 |
can also be
|
|
|
2510 |
PNG_INTRAPIXEL_DIFFERENCING)
|
|
|
2511 |
|
|
|
2512 |
png_set_PLTE(png_ptr, info_ptr, palette,
|
|
|
2513 |
num_palette);
|
|
|
2514 |
palette - the palette for the file
|
|
|
2515 |
(array of png_color)
|
|
|
2516 |
num_palette - number of entries in the palette
|
|
|
2517 |
|
|
|
2518 |
png_set_gAMA(png_ptr, info_ptr, gamma);
|
|
|
2519 |
gamma - the gamma the image was created
|
|
|
2520 |
at (PNG_INFO_gAMA)
|
|
|
2521 |
|
|
|
2522 |
png_set_sRGB(png_ptr, info_ptr, srgb_intent);
|
|
|
2523 |
srgb_intent - the rendering intent
|
|
|
2524 |
(PNG_INFO_sRGB) The presence of
|
|
|
2525 |
the sRGB chunk means that the pixel
|
|
|
2526 |
data is in the sRGB color space.
|
|
|
2527 |
This chunk also implies specific
|
|
|
2528 |
values of gAMA and cHRM. Rendering
|
|
|
2529 |
intent is the CSS-1 property that
|
|
|
2530 |
has been defined by the International
|
|
|
2531 |
Color Consortium
|
|
|
2532 |
(http://www.color.org).
|
|
|
2533 |
It can be one of
|
|
|
2534 |
PNG_sRGB_INTENT_SATURATION,
|
|
|
2535 |
PNG_sRGB_INTENT_PERCEPTUAL,
|
|
|
2536 |
PNG_sRGB_INTENT_ABSOLUTE, or
|
|
|
2537 |
PNG_sRGB_INTENT_RELATIVE.
|
|
|
2538 |
|
|
|
2539 |
|
|
|
2540 |
png_set_sRGB_gAMA_and_cHRM(png_ptr, info_ptr,
|
|
|
2541 |
srgb_intent);
|
|
|
2542 |
srgb_intent - the rendering intent
|
|
|
2543 |
(PNG_INFO_sRGB) The presence of the
|
|
|
2544 |
sRGB chunk means that the pixel
|
|
|
2545 |
data is in the sRGB color space.
|
|
|
2546 |
This function also causes gAMA and
|
|
|
2547 |
cHRM chunks with the specific values
|
|
|
2548 |
that are consistent with sRGB to be
|
|
|
2549 |
written.
|
|
|
2550 |
|
|
|
2551 |
png_set_iCCP(png_ptr, info_ptr, name, compression_type,
|
|
|
2552 |
profile, proflen);
|
|
|
2553 |
name - The profile name.
|
|
|
2554 |
compression - The compression type; always
|
|
|
2555 |
PNG_COMPRESSION_TYPE_BASE for PNG 1.0.
|
|
|
2556 |
You may give NULL to this argument to
|
|
|
2557 |
ignore it.
|
|
|
2558 |
profile - International Color Consortium color
|
|
|
2559 |
profile data. May contain NULs.
|
|
|
2560 |
proflen - length of profile data in bytes.
|
|
|
2561 |
|
|
|
2562 |
png_set_sBIT(png_ptr, info_ptr, sig_bit);
|
|
|
2563 |
sig_bit - the number of significant bits for
|
|
|
2564 |
(PNG_INFO_sBIT) each of the gray, red,
|
|
|
2565 |
green, and blue channels, whichever are
|
|
|
2566 |
appropriate for the given color type
|
|
|
2567 |
(png_color_16)
|
|
|
2568 |
|
|
|
2569 |
png_set_tRNS(png_ptr, info_ptr, trans, num_trans,
|
|
|
2570 |
trans_values);
|
|
|
2571 |
trans - array of transparent entries for
|
|
|
2572 |
palette (PNG_INFO_tRNS)
|
|
|
2573 |
trans_values - graylevel or color sample values of
|
|
|
2574 |
the single transparent color for
|
|
|
2575 |
non-paletted images (PNG_INFO_tRNS)
|
|
|
2576 |
num_trans - number of transparent entries
|
|
|
2577 |
(PNG_INFO_tRNS)
|
|
|
2578 |
|
|
|
2579 |
png_set_hIST(png_ptr, info_ptr, hist);
|
|
|
2580 |
(PNG_INFO_hIST)
|
|
|
2581 |
hist - histogram of palette (array of
|
|
|
2582 |
png_uint_16)
|
|
|
2583 |
|
|
|
2584 |
png_set_tIME(png_ptr, info_ptr, mod_time);
|
|
|
2585 |
mod_time - time image was last modified
|
|
|
2586 |
(PNG_VALID_tIME)
|
|
|
2587 |
|
|
|
2588 |
png_set_bKGD(png_ptr, info_ptr, background);
|
|
|
2589 |
background - background color (PNG_VALID_bKGD)
|
|
|
2590 |
|
|
|
2591 |
png_set_text(png_ptr, info_ptr, text_ptr, num_text);
|
|
|
2592 |
text_ptr - array of png_text holding image
|
|
|
2593 |
comments
|
|
|
2594 |
text_ptr[i].compression - type of compression used
|
|
|
2595 |
on "text" PNG_TEXT_COMPRESSION_NONE
|
|
|
2596 |
PNG_TEXT_COMPRESSION_zTXt
|
|
|
2597 |
PNG_ITXT_COMPRESSION_NONE
|
|
|
2598 |
PNG_ITXT_COMPRESSION_zTXt
|
|
|
2599 |
text_ptr[i].key - keyword for comment. Must contain
|
|
|
2600 |
1-79 characters.
|
|
|
2601 |
text_ptr[i].text - text comments for current
|
|
|
2602 |
keyword. Can be NULL or empty.
|
|
|
2603 |
text_ptr[i].text_length - length of text string,
|
|
|
2604 |
after decompression, 0 for iTXt
|
|
|
2605 |
text_ptr[i].itxt_length - length of itxt string,
|
|
|
2606 |
after decompression, 0 for tEXt/zTXt
|
|
|
2607 |
text_ptr[i].lang - language of comment (NULL or
|
|
|
2608 |
empty for unknown).
|
|
|
2609 |
text_ptr[i].translated_keyword - keyword in UTF-8 (NULL
|
|
|
2610 |
or empty for unknown).
|
|
|
2611 |
num_text - number of comments
|
|
|
2612 |
|
|
|
2613 |
png_set_sPLT(png_ptr, info_ptr, &palette_ptr,
|
|
|
2614 |
num_spalettes);
|
|
|
2615 |
palette_ptr - array of png_sPLT_struct structures
|
|
|
2616 |
to be added to the list of palettes
|
|
|
2617 |
in the info structure.
|
|
|
2618 |
num_spalettes - number of palette structures to be
|
|
|
2619 |
added.
|
|
|
2620 |
|
|
|
2621 |
png_set_oFFs(png_ptr, info_ptr, offset_x, offset_y,
|
|
|
2622 |
unit_type);
|
|
|
2623 |
offset_x - positive offset from the left
|
|
|
2624 |
edge of the screen
|
|
|
2625 |
offset_y - positive offset from the top
|
|
|
2626 |
edge of the screen
|
|
|
2627 |
unit_type - PNG_OFFSET_PIXEL, PNG_OFFSET_MICROMETER
|
|
|
2628 |
|
|
|
2629 |
png_set_pHYs(png_ptr, info_ptr, res_x, res_y,
|
|
|
2630 |
unit_type);
|
|
|
2631 |
res_x - pixels/unit physical resolution
|
|
|
2632 |
in x direction
|
|
|
2633 |
res_y - pixels/unit physical resolution
|
|
|
2634 |
in y direction
|
|
|
2635 |
unit_type - PNG_RESOLUTION_UNKNOWN,
|
|
|
2636 |
PNG_RESOLUTION_METER
|
|
|
2637 |
|
|
|
2638 |
png_set_sCAL(png_ptr, info_ptr, unit, width, height)
|
|
|
2639 |
unit - physical scale units (an integer)
|
|
|
2640 |
width - width of a pixel in physical scale units
|
|
|
2641 |
height - height of a pixel in physical scale units
|
|
|
2642 |
(width and height are doubles)
|
|
|
2643 |
|
|
|
2644 |
png_set_sCAL_s(png_ptr, info_ptr, unit, width, height)
|
|
|
2645 |
unit - physical scale units (an integer)
|
|
|
2646 |
width - width of a pixel in physical scale units
|
|
|
2647 |
height - height of a pixel in physical scale units
|
|
|
2648 |
(width and height are strings like "2.54")
|
|
|
2649 |
|
|
|
2650 |
png_set_unknown_chunks(png_ptr, info_ptr, &unknowns,
|
|
|
2651 |
num_unknowns)
|
|
|
2652 |
unknowns - array of png_unknown_chunk
|
|
|
2653 |
structures holding unknown chunks
|
|
|
2654 |
unknowns[i].name - name of unknown chunk
|
|
|
2655 |
unknowns[i].data - data of unknown chunk
|
|
|
2656 |
unknowns[i].size - size of unknown chunk's data
|
|
|
2657 |
unknowns[i].location - position to write chunk in file
|
|
|
2658 |
0: do not write chunk
|
|
|
2659 |
PNG_HAVE_IHDR: before PLTE
|
|
|
2660 |
PNG_HAVE_PLTE: before IDAT
|
|
|
2661 |
PNG_AFTER_IDAT: after IDAT
|
|
|
2662 |
|
|
|
2663 |
The "location" member is set automatically according to
|
|
|
2664 |
what part of the output file has already been written.
|
|
|
2665 |
You can change its value after calling png_set_unknown_chunks()
|
|
|
2666 |
as demonstrated in pngtest.c. Within each of the "locations",
|
|
|
2667 |
the chunks are sequenced according to their position in the
|
|
|
2668 |
structure (that is, the value of "i", which is the order in which
|
|
|
2669 |
the chunk was either read from the input file or defined with
|
|
|
2670 |
png_set_unknown_chunks).
|
|
|
2671 |
|
|
|
2672 |
A quick word about text and num_text. text is an array of png_text
|
|
|
2673 |
structures. num_text is the number of valid structures in the array.
|
|
|
2674 |
Each png_text structure holds a language code, a keyword, a text value,
|
|
|
2675 |
and a compression type.
|
|
|
2676 |
|
|
|
2677 |
The compression types have the same valid numbers as the compression
|
|
|
2678 |
types of the image data. Currently, the only valid number is zero.
|
|
|
2679 |
However, you can store text either compressed or uncompressed, unlike
|
|
|
2680 |
images, which always have to be compressed. So if you don't want the
|
|
|
2681 |
text compressed, set the compression type to PNG_TEXT_COMPRESSION_NONE.
|
|
|
2682 |
Because tEXt and zTXt chunks don't have a language field, if you
|
|
|
2683 |
specify PNG_TEXT_COMPRESSION_NONE or PNG_TEXT_COMPRESSION_zTXt
|
|
|
2684 |
any language code or translated keyword will not be written out.
|
|
|
2685 |
|
|
|
2686 |
Until text gets around 1000 bytes, it is not worth compressing it.
|
|
|
2687 |
After the text has been written out to the file, the compression type
|
|
|
2688 |
is set to PNG_TEXT_COMPRESSION_NONE_WR or PNG_TEXT_COMPRESSION_zTXt_WR,
|
|
|
2689 |
so that it isn't written out again at the end (in case you are calling
|
|
|
2690 |
png_write_end() with the same struct.
|
|
|
2691 |
|
|
|
2692 |
The keywords that are given in the PNG Specification are:
|
|
|
2693 |
|
|
|
2694 |
Title Short (one line) title or
|
|
|
2695 |
caption for image
|
|
|
2696 |
Author Name of image's creator
|
|
|
2697 |
Description Description of image (possibly long)
|
|
|
2698 |
Copyright Copyright notice
|
|
|
2699 |
Creation Time Time of original image creation
|
|
|
2700 |
(usually RFC 1123 format, see below)
|
|
|
2701 |
Software Software used to create the image
|
|
|
2702 |
Disclaimer Legal disclaimer
|
|
|
2703 |
Warning Warning of nature of content
|
|
|
2704 |
Source Device used to create the image
|
|
|
2705 |
Comment Miscellaneous comment; conversion
|
|
|
2706 |
from other image format
|
|
|
2707 |
|
|
|
2708 |
The keyword-text pairs work like this. Keywords should be short
|
|
|
2709 |
simple descriptions of what the comment is about. Some typical
|
|
|
2710 |
keywords are found in the PNG specification, as is some recommendations
|
|
|
2711 |
on keywords. You can repeat keywords in a file. You can even write
|
|
|
2712 |
some text before the image and some after. For example, you may want
|
|
|
2713 |
to put a description of the image before the image, but leave the
|
|
|
2714 |
disclaimer until after, so viewers working over modem connections
|
|
|
2715 |
don't have to wait for the disclaimer to go over the modem before
|
|
|
2716 |
they start seeing the image. Finally, keywords should be full
|
|
|
2717 |
words, not abbreviations. Keywords and text are in the ISO 8859-1
|
|
|
2718 |
(Latin-1) character set (a superset of regular ASCII) and can not
|
|
|
2719 |
contain NUL characters, and should not contain control or other
|
|
|
2720 |
unprintable characters. To make the comments widely readable, stick
|
|
|
2721 |
with basic ASCII, and avoid machine specific character set extensions
|
|
|
2722 |
like the IBM-PC character set. The keyword must be present, but
|
|
|
2723 |
you can leave off the text string on non-compressed pairs.
|
|
|
2724 |
Compressed pairs must have a text string, as only the text string
|
|
|
2725 |
is compressed anyway, so the compression would be meaningless.
|
|
|
2726 |
|
|
|
2727 |
PNG supports modification time via the png_time structure. Two
|
|
|
2728 |
conversion routines are provided, png_convert_from_time_t() for
|
|
|
2729 |
time_t and png_convert_from_struct_tm() for struct tm. The
|
|
|
2730 |
time_t routine uses gmtime(). You don't have to use either of
|
|
|
2731 |
these, but if you wish to fill in the png_time structure directly,
|
|
|
2732 |
you should provide the time in universal time (GMT) if possible
|
|
|
2733 |
instead of your local time. Note that the year number is the full
|
|
|
2734 |
year (e.g. 1998, rather than 98 - PNG is year 2000 compliant!), and
|
|
|
2735 |
that months start with 1.
|
|
|
2736 |
|
|
|
2737 |
If you want to store the time of the original image creation, you should
|
|
|
2738 |
use a plain tEXt chunk with the "Creation Time" keyword. This is
|
|
|
2739 |
necessary because the "creation time" of a PNG image is somewhat vague,
|
|
|
2740 |
depending on whether you mean the PNG file, the time the image was
|
|
|
2741 |
created in a non-PNG format, a still photo from which the image was
|
|
|
2742 |
scanned, or possibly the subject matter itself. In order to facilitate
|
|
|
2743 |
machine-readable dates, it is recommended that the "Creation Time"
|
|
|
2744 |
tEXt chunk use RFC 1123 format dates (e.g. "22 May 1997 18:07:10 GMT"),
|
|
|
2745 |
although this isn't a requirement. Unlike the tIME chunk, the
|
|
|
2746 |
"Creation Time" tEXt chunk is not expected to be automatically changed
|
|
|
2747 |
by the software. To facilitate the use of RFC 1123 dates, a function
|
|
|
2748 |
png_convert_to_rfc1123(png_timep) is provided to convert from PNG
|
|
|
2749 |
time to an RFC 1123 format string.
|
|
|
2750 |
|
|
|
2751 |
.SS Writing unknown chunks
|
|
|
2752 |
|
|
|
2753 |
You can use the png_set_unknown_chunks function to queue up chunks
|
|
|
2754 |
for writing. You give it a chunk name, raw data, and a size; that's
|
|
|
2755 |
all there is to it. The chunks will be written by the next following
|
|
|
2756 |
png_write_info_before_PLTE, png_write_info, or png_write_end function.
|
|
|
2757 |
Any chunks previously read into the info structure's unknown-chunk
|
|
|
2758 |
list will also be written out in a sequence that satisfies the PNG
|
|
|
2759 |
specification's ordering rules.
|
|
|
2760 |
|
|
|
2761 |
.SS The high-level write interface
|
|
|
2762 |
|
|
|
2763 |
At this point there are two ways to proceed; through the high-level
|
|
|
2764 |
write interface, or through a sequence of low-level write operations.
|
|
|
2765 |
You can use the high-level interface if your image data is present
|
|
|
2766 |
in the info structure. All defined output
|
|
|
2767 |
transformations are permitted, enabled by the following masks.
|
|
|
2768 |
|
|
|
2769 |
PNG_TRANSFORM_IDENTITY No transformation
|
|
|
2770 |
PNG_TRANSFORM_PACKING Pack 1, 2 and 4-bit samples
|
|
|
2771 |
PNG_TRANSFORM_PACKSWAP Change order of packed
|
|
|
2772 |
pixels to LSB first
|
|
|
2773 |
PNG_TRANSFORM_INVERT_MONO Invert monochrome images
|
|
|
2774 |
PNG_TRANSFORM_SHIFT Normalize pixels to the
|
|
|
2775 |
sBIT depth
|
|
|
2776 |
PNG_TRANSFORM_BGR Flip RGB to BGR, RGBA
|
|
|
2777 |
to BGRA
|
|
|
2778 |
PNG_TRANSFORM_SWAP_ALPHA Flip RGBA to ARGB or GA
|
|
|
2779 |
to AG
|
|
|
2780 |
PNG_TRANSFORM_INVERT_ALPHA Change alpha from opacity
|
|
|
2781 |
to transparency
|
|
|
2782 |
PNG_TRANSFORM_SWAP_ENDIAN Byte-swap 16-bit samples
|
|
|
2783 |
PNG_TRANSFORM_STRIP_FILLER Strip out filler bytes.
|
|
|
2784 |
|
|
|
2785 |
If you have valid image data in the info structure (you can use
|
|
|
2786 |
png_set_rows() to put image data in the info structure), simply do this:
|
|
|
2787 |
|
|
|
2788 |
png_write_png(png_ptr, info_ptr, png_transforms, NULL)
|
|
|
2789 |
|
|
|
2790 |
where png_transforms is an integer containing the logical OR of some set of
|
|
|
2791 |
transformation flags. This call is equivalent to png_write_info(),
|
|
|
2792 |
followed the set of transformations indicated by the transform mask,
|
|
|
2793 |
then png_write_image(), and finally png_write_end().
|
|
|
2794 |
|
|
|
2795 |
(The final parameter of this call is not yet used. Someday it might point
|
|
|
2796 |
to transformation parameters required by some future output transform.)
|
|
|
2797 |
|
|
|
2798 |
You must use png_transforms and not call any png_set_transform() functions
|
|
|
2799 |
when you use png_write_png().
|
|
|
2800 |
|
|
|
2801 |
.SS The low-level write interface
|
|
|
2802 |
|
|
|
2803 |
If you are going the low-level route instead, you are now ready to
|
|
|
2804 |
write all the file information up to the actual image data. You do
|
|
|
2805 |
this with a call to png_write_info().
|
|
|
2806 |
|
|
|
2807 |
png_write_info(png_ptr, info_ptr);
|
|
|
2808 |
|
|
|
2809 |
Note that there is one transformation you may need to do before
|
|
|
2810 |
png_write_info(). In PNG files, the alpha channel in an image is the
|
|
|
2811 |
level of opacity. If your data is supplied as a level of
|
|
|
2812 |
transparency, you can invert the alpha channel before you write it, so
|
|
|
2813 |
that 0 is fully transparent and 255 (in 8-bit or paletted images) or
|
|
|
2814 |
65535 (in 16-bit images) is fully opaque, with
|
|
|
2815 |
|
|
|
2816 |
png_set_invert_alpha(png_ptr);
|
|
|
2817 |
|
|
|
2818 |
This must appear before png_write_info() instead of later with the
|
|
|
2819 |
other transformations because in the case of paletted images the tRNS
|
|
|
2820 |
chunk data has to be inverted before the tRNS chunk is written. If
|
|
|
2821 |
your image is not a paletted image, the tRNS data (which in such cases
|
|
|
2822 |
represents a single color to be rendered as transparent) won't need to
|
|
|
2823 |
be changed, and you can safely do this transformation after your
|
|
|
2824 |
png_write_info() call.
|
|
|
2825 |
|
|
|
2826 |
If you need to write a private chunk that you want to appear before
|
|
|
2827 |
the PLTE chunk when PLTE is present, you can write the PNG info in
|
|
|
2828 |
two steps, and insert code to write your own chunk between them:
|
|
|
2829 |
|
|
|
2830 |
png_write_info_before_PLTE(png_ptr, info_ptr);
|
|
|
2831 |
png_set_unknown_chunks(png_ptr, info_ptr, ...);
|
|
|
2832 |
png_write_info(png_ptr, info_ptr);
|
|
|
2833 |
|
|
|
2834 |
After you've written the file information, you can set up the library
|
|
|
2835 |
to handle any special transformations of the image data. The various
|
|
|
2836 |
ways to transform the data will be described in the order that they
|
|
|
2837 |
should occur. This is important, as some of these change the color
|
|
|
2838 |
type and/or bit depth of the data, and some others only work on
|
|
|
2839 |
certain color types and bit depths. Even though each transformation
|
|
|
2840 |
checks to see if it has data that it can do something with, you should
|
|
|
2841 |
make sure to only enable a transformation if it will be valid for the
|
|
|
2842 |
data. For example, don't swap red and blue on grayscale data.
|
|
|
2843 |
|
|
|
2844 |
PNG files store RGB pixels packed into 3 or 6 bytes. This code tells
|
|
|
2845 |
the library to strip input data that has 4 or 8 bytes per pixel down
|
|
|
2846 |
to 3 or 6 bytes (or strip 2 or 4-byte grayscale+filler data to 1 or 2
|
|
|
2847 |
bytes per pixel).
|
|
|
2848 |
|
|
|
2849 |
png_set_filler(png_ptr, 0, PNG_FILLER_BEFORE);
|
|
|
2850 |
|
|
|
2851 |
where the 0 is unused, and the location is either PNG_FILLER_BEFORE or
|
|
|
2852 |
PNG_FILLER_AFTER, depending upon whether the filler byte in the pixel
|
|
|
2853 |
is stored XRGB or RGBX.
|
|
|
2854 |
|
|
|
2855 |
PNG files pack pixels of bit depths 1, 2, and 4 into bytes as small as
|
|
|
2856 |
they can, resulting in, for example, 8 pixels per byte for 1 bit files.
|
|
|
2857 |
If the data is supplied at 1 pixel per byte, use this code, which will
|
|
|
2858 |
correctly pack the pixels into a single byte:
|
|
|
2859 |
|
|
|
2860 |
png_set_packing(png_ptr);
|
|
|
2861 |
|
|
|
2862 |
PNG files reduce possible bit depths to 1, 2, 4, 8, and 16. If your
|
|
|
2863 |
data is of another bit depth, you can write an sBIT chunk into the
|
|
|
2864 |
file so that decoders can recover the original data if desired.
|
|
|
2865 |
|
|
|
2866 |
/* Set the true bit depth of the image data */
|
|
|
2867 |
if (color_type & PNG_COLOR_MASK_COLOR)
|
|
|
2868 |
{
|
|
|
2869 |
sig_bit.red = true_bit_depth;
|
|
|
2870 |
sig_bit.green = true_bit_depth;
|
|
|
2871 |
sig_bit.blue = true_bit_depth;
|
|
|
2872 |
}
|
|
|
2873 |
else
|
|
|
2874 |
{
|
|
|
2875 |
sig_bit.gray = true_bit_depth;
|
|
|
2876 |
}
|
|
|
2877 |
if (color_type & PNG_COLOR_MASK_ALPHA)
|
|
|
2878 |
{
|
|
|
2879 |
sig_bit.alpha = true_bit_depth;
|
|
|
2880 |
}
|
|
|
2881 |
|
|
|
2882 |
png_set_sBIT(png_ptr, info_ptr, &sig_bit);
|
|
|
2883 |
|
|
|
2884 |
If the data is stored in the row buffer in a bit depth other than
|
|
|
2885 |
one supported by PNG (e.g. 3 bit data in the range 0-7 for a 4-bit PNG),
|
|
|
2886 |
this will scale the values to appear to be the correct bit depth as
|
|
|
2887 |
is required by PNG.
|
|
|
2888 |
|
|
|
2889 |
png_set_shift(png_ptr, &sig_bit);
|
|
|
2890 |
|
|
|
2891 |
PNG files store 16 bit pixels in network byte order (big-endian,
|
|
|
2892 |
ie. most significant bits first). This code would be used if they are
|
|
|
2893 |
supplied the other way (little-endian, i.e. least significant bits
|
|
|
2894 |
first, the way PCs store them):
|
|
|
2895 |
|
|
|
2896 |
if (bit_depth > 8)
|
|
|
2897 |
png_set_swap(png_ptr);
|
|
|
2898 |
|
|
|
2899 |
If you are using packed-pixel images (1, 2, or 4 bits/pixel), and you
|
|
|
2900 |
need to change the order the pixels are packed into bytes, you can use:
|
|
|
2901 |
|
|
|
2902 |
if (bit_depth < 8)
|
|
|
2903 |
png_set_packswap(png_ptr);
|
|
|
2904 |
|
|
|
2905 |
PNG files store 3 color pixels in red, green, blue order. This code
|
|
|
2906 |
would be used if they are supplied as blue, green, red:
|
|
|
2907 |
|
|
|
2908 |
png_set_bgr(png_ptr);
|
|
|
2909 |
|
|
|
2910 |
PNG files describe monochrome as black being zero and white being
|
|
|
2911 |
one. This code would be used if the pixels are supplied with this reversed
|
|
|
2912 |
(black being one and white being zero):
|
|
|
2913 |
|
|
|
2914 |
png_set_invert_mono(png_ptr);
|
|
|
2915 |
|
|
|
2916 |
Finally, you can write your own transformation function if none of
|
|
|
2917 |
the existing ones meets your needs. This is done by setting a callback
|
|
|
2918 |
with
|
|
|
2919 |
|
|
|
2920 |
png_set_write_user_transform_fn(png_ptr,
|
|
|
2921 |
write_transform_fn);
|
|
|
2922 |
|
|
|
2923 |
You must supply the function
|
|
|
2924 |
|
|
|
2925 |
void write_transform_fn(png_ptr ptr, row_info_ptr
|
|
|
2926 |
row_info, png_bytep data)
|
|
|
2927 |
|
|
|
2928 |
See pngtest.c for a working example. Your function will be called
|
|
|
2929 |
before any of the other transformations are processed.
|
|
|
2930 |
|
|
|
2931 |
You can also set up a pointer to a user structure for use by your
|
|
|
2932 |
callback function.
|
|
|
2933 |
|
|
|
2934 |
png_set_user_transform_info(png_ptr, user_ptr, 0, 0);
|
|
|
2935 |
|
|
|
2936 |
The user_channels and user_depth parameters of this function are ignored
|
|
|
2937 |
when writing; you can set them to zero as shown.
|
|
|
2938 |
|
|
|
2939 |
You can retrieve the pointer via the function png_get_user_transform_ptr().
|
|
|
2940 |
For example:
|
|
|
2941 |
|
|
|
2942 |
voidp write_user_transform_ptr =
|
|
|
2943 |
png_get_user_transform_ptr(png_ptr);
|
|
|
2944 |
|
|
|
2945 |
It is possible to have libpng flush any pending output, either manually,
|
|
|
2946 |
or automatically after a certain number of lines have been written. To
|
|
|
2947 |
flush the output stream a single time call:
|
|
|
2948 |
|
|
|
2949 |
png_write_flush(png_ptr);
|
|
|
2950 |
|
|
|
2951 |
and to have libpng flush the output stream periodically after a certain
|
|
|
2952 |
number of scanlines have been written, call:
|
|
|
2953 |
|
|
|
2954 |
png_set_flush(png_ptr, nrows);
|
|
|
2955 |
|
|
|
2956 |
Note that the distance between rows is from the last time png_write_flush()
|
|
|
2957 |
was called, or the first row of the image if it has never been called.
|
|
|
2958 |
So if you write 50 lines, and then png_set_flush 25, it will flush the
|
|
|
2959 |
output on the next scanline, and every 25 lines thereafter, unless
|
|
|
2960 |
png_write_flush() is called before 25 more lines have been written.
|
|
|
2961 |
If nrows is too small (less than about 10 lines for a 640 pixel wide
|
|
|
2962 |
RGB image) the image compression may decrease noticeably (although this
|
|
|
2963 |
may be acceptable for real-time applications). Infrequent flushing will
|
|
|
2964 |
only degrade the compression performance by a few percent over images
|
|
|
2965 |
that do not use flushing.
|
|
|
2966 |
|
|
|
2967 |
.SS Writing the image data
|
|
|
2968 |
|
|
|
2969 |
That's it for the transformations. Now you can write the image data.
|
|
|
2970 |
The simplest way to do this is in one function call. If you have the
|
|
|
2971 |
whole image in memory, you can just call png_write_image() and libpng
|
|
|
2972 |
will write the image. You will need to pass in an array of pointers to
|
|
|
2973 |
each row. This function automatically handles interlacing, so you don't
|
|
|
2974 |
need to call png_set_interlace_handling() or call this function multiple
|
|
|
2975 |
times, or any of that other stuff necessary with png_write_rows().
|
|
|
2976 |
|
|
|
2977 |
png_write_image(png_ptr, row_pointers);
|
|
|
2978 |
|
|
|
2979 |
where row_pointers is:
|
|
|
2980 |
|
|
|
2981 |
png_byte *row_pointers[height];
|
|
|
2982 |
|
|
|
2983 |
You can point to void or char or whatever you use for pixels.
|
|
|
2984 |
|
|
|
2985 |
If you don't want to write the whole image at once, you can
|
|
|
2986 |
use png_write_rows() instead. If the file is not interlaced,
|
|
|
2987 |
this is simple:
|
|
|
2988 |
|
|
|
2989 |
png_write_rows(png_ptr, row_pointers,
|
|
|
2990 |
number_of_rows);
|
|
|
2991 |
|
|
|
2992 |
row_pointers is the same as in the png_write_image() call.
|
|
|
2993 |
|
|
|
2994 |
If you are just writing one row at a time, you can do this with
|
|
|
2995 |
a single row_pointer instead of an array of row_pointers:
|
|
|
2996 |
|
|
|
2997 |
png_bytep row_pointer = row;
|
|
|
2998 |
|
|
|
2999 |
png_write_row(png_ptr, row_pointer);
|
|
|
3000 |
|
|
|
3001 |
When the file is interlaced, things can get a good deal more
|
|
|
3002 |
complicated. The only currently (as of the PNG Specification
|
|
|
3003 |
version 1.2, dated July 1999) defined interlacing scheme for PNG files
|
|
|
3004 |
is the "Adam7" interlace scheme, that breaks down an
|
|
|
3005 |
image into seven smaller images of varying size. libpng will build
|
|
|
3006 |
these images for you, or you can do them yourself. If you want to
|
|
|
3007 |
build them yourself, see the PNG specification for details of which
|
|
|
3008 |
pixels to write when.
|
|
|
3009 |
|
|
|
3010 |
If you don't want libpng to handle the interlacing details, just
|
|
|
3011 |
use png_set_interlace_handling() and call png_write_rows() the
|
|
|
3012 |
correct number of times to write all seven sub-images.
|
|
|
3013 |
|
|
|
3014 |
If you want libpng to build the sub-images, call this before you start
|
|
|
3015 |
writing any rows:
|
|
|
3016 |
|
|
|
3017 |
number_of_passes =
|
|
|
3018 |
png_set_interlace_handling(png_ptr);
|
|
|
3019 |
|
|
|
3020 |
This will return the number of passes needed. Currently, this
|
|
|
3021 |
is seven, but may change if another interlace type is added.
|
|
|
3022 |
|
|
|
3023 |
Then write the complete image number_of_passes times.
|
|
|
3024 |
|
|
|
3025 |
png_write_rows(png_ptr, row_pointers,
|
|
|
3026 |
number_of_rows);
|
|
|
3027 |
|
|
|
3028 |
As some of these rows are not used, and thus return immediately,
|
|
|
3029 |
you may want to read about interlacing in the PNG specification,
|
|
|
3030 |
and only update the rows that are actually used.
|
|
|
3031 |
|
|
|
3032 |
.SS Finishing a sequential write
|
|
|
3033 |
|
|
|
3034 |
After you are finished writing the image, you should finish writing
|
|
|
3035 |
the file. If you are interested in writing comments or time, you should
|
|
|
3036 |
pass an appropriately filled png_info pointer. If you are not interested,
|
|
|
3037 |
you can pass NULL.
|
|
|
3038 |
|
|
|
3039 |
png_write_end(png_ptr, info_ptr);
|
|
|
3040 |
|
|
|
3041 |
When you are done, you can free all memory used by libpng like this:
|
|
|
3042 |
|
|
|
3043 |
png_destroy_write_struct(&png_ptr, &info_ptr);
|
|
|
3044 |
|
|
|
3045 |
It is also possible to individually free the info_ptr members that
|
|
|
3046 |
point to libpng-allocated storage with the following function:
|
|
|
3047 |
|
|
|
3048 |
png_free_data(png_ptr, info_ptr, mask, seq)
|
|
|
3049 |
mask - identifies data to be freed, a mask
|
|
|
3050 |
containing the logical OR of one or
|
|
|
3051 |
more of
|
|
|
3052 |
PNG_FREE_PLTE, PNG_FREE_TRNS,
|
|
|
3053 |
PNG_FREE_HIST, PNG_FREE_ICCP,
|
|
|
3054 |
PNG_FREE_PCAL, PNG_FREE_ROWS,
|
|
|
3055 |
PNG_FREE_SCAL, PNG_FREE_SPLT,
|
|
|
3056 |
PNG_FREE_TEXT, PNG_FREE_UNKN,
|
|
|
3057 |
or simply PNG_FREE_ALL
|
|
|
3058 |
seq - sequence number of item to be freed
|
|
|
3059 |
(-1 for all items)
|
|
|
3060 |
|
|
|
3061 |
This function may be safely called when the relevant storage has
|
|
|
3062 |
already been freed, or has not yet been allocated, or was allocated
|
|
|
3063 |
by the user and not by libpng, and will in those
|
|
|
3064 |
cases do nothing. The "seq" parameter is ignored if only one item
|
|
|
3065 |
of the selected data type, such as PLTE, is allowed. If "seq" is not
|
|
|
3066 |
-1, and multiple items are allowed for the data type identified in
|
|
|
3067 |
the mask, such as text or sPLT, only the n'th item in the structure
|
|
|
3068 |
is freed, where n is "seq".
|
|
|
3069 |
|
|
|
3070 |
If you allocated data such as a palette that you passed
|
|
|
3071 |
in to libpng with png_set_*, you must not free it until just before the call to
|
|
|
3072 |
png_destroy_write_struct().
|
|
|
3073 |
|
|
|
3074 |
The default behavior is only to free data that was allocated internally
|
|
|
3075 |
by libpng. This can be changed, so that libpng will not free the data,
|
|
|
3076 |
or so that it will free data that was allocated by the user with png_malloc()
|
|
|
3077 |
or png_zalloc() and passed in via a png_set_*() function, with
|
|
|
3078 |
|
|
|
3079 |
png_data_freer(png_ptr, info_ptr, freer, mask)
|
|
|
3080 |
mask - which data elements are affected
|
|
|
3081 |
same choices as in png_free_data()
|
|
|
3082 |
freer - one of
|
|
|
3083 |
PNG_DESTROY_WILL_FREE_DATA
|
|
|
3084 |
PNG_SET_WILL_FREE_DATA
|
|
|
3085 |
PNG_USER_WILL_FREE_DATA
|
|
|
3086 |
|
|
|
3087 |
For example, to transfer responsibility for some data from a read structure
|
|
|
3088 |
to a write structure, you could use
|
|
|
3089 |
|
|
|
3090 |
png_data_freer(read_ptr, read_info_ptr,
|
|
|
3091 |
PNG_USER_WILL_FREE_DATA,
|
|
|
3092 |
PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
|
|
|
3093 |
png_data_freer(write_ptr, write_info_ptr,
|
|
|
3094 |
PNG_DESTROY_WILL_FREE_DATA,
|
|
|
3095 |
PNG_FREE_PLTE|PNG_FREE_tRNS|PNG_FREE_hIST)
|
|
|
3096 |
|
|
|
3097 |
thereby briefly reassigning responsibility for freeing to the user but
|
|
|
3098 |
immediately afterwards reassigning it once more to the write_destroy
|
|
|
3099 |
function. Having done this, it would then be safe to destroy the read
|
|
|
3100 |
structure and continue to use the PLTE, tRNS, and hIST data in the write
|
|
|
3101 |
structure.
|
|
|
3102 |
|
|
|
3103 |
This function only affects data that has already been allocated.
|
|
|
3104 |
You can call this function before calling after the png_set_*() functions
|
|
|
3105 |
to control whether the user or png_destroy_*() is supposed to free the data.
|
|
|
3106 |
When the user assumes responsibility for libpng-allocated data, the
|
|
|
3107 |
application must use
|
|
|
3108 |
png_free() to free it, and when the user transfers responsibility to libpng
|
|
|
3109 |
for data that the user has allocated, the user must have used png_malloc()
|
|
|
3110 |
or png_zalloc() to allocate it.
|
|
|
3111 |
|
|
|
3112 |
If you allocated text_ptr.text, text_ptr.lang, and text_ptr.translated_keyword
|
|
|
3113 |
separately, do not transfer responsibility for freeing text_ptr to libpng,
|
|
|
3114 |
because when libpng fills a png_text structure it combines these members with
|
|
|
3115 |
the key member, and png_free_data() will free only text_ptr.key. Similarly,
|
|
|
3116 |
if you transfer responsibility for free'ing text_ptr from libpng to your
|
|
|
3117 |
application, your application must not separately free those members.
|
|
|
3118 |
For a more compact example of writing a PNG image, see the file example.c.
|
|
|
3119 |
|
|
|
3120 |
.SH V. Modifying/Customizing libpng:
|
|
|
3121 |
|
|
|
3122 |
There are three issues here. The first is changing how libpng does
|
|
|
3123 |
standard things like memory allocation, input/output, and error handling.
|
|
|
3124 |
The second deals with more complicated things like adding new chunks,
|
|
|
3125 |
adding new transformations, and generally changing how libpng works.
|
|
|
3126 |
Both of those are compile-time issues; that is, they are generally
|
|
|
3127 |
determined at the time the code is written, and there is rarely a need
|
|
|
3128 |
to provide the user with a means of changing them. The third is a
|
|
|
3129 |
run-time issue: choosing between and/or tuning one or more alternate
|
|
|
3130 |
versions of computationally intensive routines; specifically, optimized
|
|
|
3131 |
assembly-language (and therefore compiler- and platform-dependent)
|
|
|
3132 |
versions.
|
|
|
3133 |
|
|
|
3134 |
Memory allocation, input/output, and error handling
|
|
|
3135 |
|
|
|
3136 |
All of the memory allocation, input/output, and error handling in libpng
|
|
|
3137 |
goes through callbacks that are user-settable. The default routines are
|
|
|
3138 |
in pngmem.c, pngrio.c, pngwio.c, and pngerror.c, respectively. To change
|
|
|
3139 |
these functions, call the appropriate png_set_*_fn() function.
|
|
|
3140 |
|
|
|
3141 |
Memory allocation is done through the functions png_malloc()
|
|
|
3142 |
and png_free(). These currently just call the standard C functions. If
|
|
|
3143 |
your pointers can't access more then 64K at a time, you will want to set
|
|
|
3144 |
MAXSEG_64K in zlib.h. Since it is unlikely that the method of handling
|
|
|
3145 |
memory allocation on a platform will change between applications, these
|
|
|
3146 |
functions must be modified in the library at compile time. If you prefer
|
|
|
3147 |
to use a different method of allocating and freeing data, you can use
|
|
|
3148 |
png_create_read_struct_2() or png_create_write_struct_2() to register
|
|
|
3149 |
your own functions as described above.
|
|
|
3150 |
These functions also provide a void pointer that can be retrieved via
|
|
|
3151 |
|
|
|
3152 |
mem_ptr=png_get_mem_ptr(png_ptr);
|
|
|
3153 |
|
|
|
3154 |
Your replacement memory functions must have prototypes as follows:
|
|
|
3155 |
|
|
|
3156 |
png_voidp malloc_fn(png_structp png_ptr,
|
|
|
3157 |
png_size_t size);
|
|
|
3158 |
void free_fn(png_structp png_ptr, png_voidp ptr);
|
|
|
3159 |
|
|
|
3160 |
Your malloc_fn() must return NULL in case of failure. The png_malloc()
|
|
|
3161 |
function will normally call png_error() if it receives a NULL from the
|
|
|
3162 |
system memory allocator or from your replacement malloc_fn().
|
|
|
3163 |
|
|
|
3164 |
Input/Output in libpng is done through png_read() and png_write(),
|
|
|
3165 |
which currently just call fread() and fwrite(). The FILE * is stored in
|
|
|
3166 |
png_struct and is initialized via png_init_io(). If you wish to change
|
|
|
3167 |
the method of I/O, the library supplies callbacks that you can set
|
|
|
3168 |
through the function png_set_read_fn() and png_set_write_fn() at run
|
|
|
3169 |
time, instead of calling the png_init_io() function. These functions
|
|
|
3170 |
also provide a void pointer that can be retrieved via the function
|
|
|
3171 |
png_get_io_ptr(). For example:
|
|
|
3172 |
|
|
|
3173 |
png_set_read_fn(png_structp read_ptr,
|
|
|
3174 |
voidp read_io_ptr, png_rw_ptr read_data_fn)
|
|
|
3175 |
|
|
|
3176 |
png_set_write_fn(png_structp write_ptr,
|
|
|
3177 |
voidp write_io_ptr, png_rw_ptr write_data_fn,
|
|
|
3178 |
png_flush_ptr output_flush_fn);
|
|
|
3179 |
|
|
|
3180 |
voidp read_io_ptr = png_get_io_ptr(read_ptr);
|
|
|
3181 |
voidp write_io_ptr = png_get_io_ptr(write_ptr);
|
|
|
3182 |
|
|
|
3183 |
The replacement I/O functions must have prototypes as follows:
|
|
|
3184 |
|
|
|
3185 |
void user_read_data(png_structp png_ptr,
|
|
|
3186 |
png_bytep data, png_size_t length);
|
|
|
3187 |
void user_write_data(png_structp png_ptr,
|
|
|
3188 |
png_bytep data, png_size_t length);
|
|
|
3189 |
void user_flush_data(png_structp png_ptr);
|
|
|
3190 |
|
|
|
3191 |
Supplying NULL for the read, write, or flush functions sets them back
|
|
|
3192 |
to using the default C stream functions. It is an error to read from
|
|
|
3193 |
a write stream, and vice versa.
|
|
|
3194 |
|
|
|
3195 |
Error handling in libpng is done through png_error() and png_warning().
|
|
|
3196 |
Errors handled through png_error() are fatal, meaning that png_error()
|
|
|
3197 |
should never return to its caller. Currently, this is handled via
|
|
|
3198 |
setjmp() and longjmp() (unless you have compiled libpng with
|
|
|
3199 |
PNG_SETJMP_NOT_SUPPORTED, in which case it is handled via PNG_ABORT()),
|
|
|
3200 |
but you could change this to do things like exit() if you should wish.
|
|
|
3201 |
|
|
|
3202 |
On non-fatal errors, png_warning() is called
|
|
|
3203 |
to print a warning message, and then control returns to the calling code.
|
|
|
3204 |
By default png_error() and png_warning() print a message on stderr via
|
|
|
3205 |
fprintf() unless the library is compiled with PNG_NO_CONSOLE_IO defined
|
|
|
3206 |
(because you don't want the messages) or PNG_NO_STDIO defined (because
|
|
|
3207 |
fprintf() isn't available). If you wish to change the behavior of the error
|
|
|
3208 |
functions, you will need to set up your own message callbacks. These
|
|
|
3209 |
functions are normally supplied at the time that the png_struct is created.
|
|
|
3210 |
It is also possible to redirect errors and warnings to your own replacement
|
|
|
3211 |
functions after png_create_*_struct() has been called by calling:
|
|
|
3212 |
|
|
|
3213 |
png_set_error_fn(png_structp png_ptr,
|
|
|
3214 |
png_voidp error_ptr, png_error_ptr error_fn,
|
|
|
3215 |
png_error_ptr warning_fn);
|
|
|
3216 |
|
|
|
3217 |
png_voidp error_ptr = png_get_error_ptr(png_ptr);
|
|
|
3218 |
|
|
|
3219 |
If NULL is supplied for either error_fn or warning_fn, then the libpng
|
|
|
3220 |
default function will be used, calling fprintf() and/or longjmp() if a
|
|
|
3221 |
problem is encountered. The replacement error functions should have
|
|
|
3222 |
parameters as follows:
|
|
|
3223 |
|
|
|
3224 |
void user_error_fn(png_structp png_ptr,
|
|
|
3225 |
png_const_charp error_msg);
|
|
|
3226 |
void user_warning_fn(png_structp png_ptr,
|
|
|
3227 |
png_const_charp warning_msg);
|
|
|
3228 |
|
|
|
3229 |
The motivation behind using setjmp() and longjmp() is the C++ throw and
|
|
|
3230 |
catch exception handling methods. This makes the code much easier to write,
|
|
|
3231 |
as there is no need to check every return code of every function call.
|
|
|
3232 |
However, there are some uncertainties about the status of local variables
|
|
|
3233 |
after a longjmp, so the user may want to be careful about doing anything after
|
|
|
3234 |
setjmp returns non-zero besides returning itself. Consult your compiler
|
|
|
3235 |
documentation for more details. For an alternative approach, you may wish
|
|
|
3236 |
to use the "cexcept" facility (see http://cexcept.sourceforge.net).
|
|
|
3237 |
|
|
|
3238 |
.SS Custom chunks
|
|
|
3239 |
|
|
|
3240 |
If you need to read or write custom chunks, you may need to get deeper
|
|
|
3241 |
into the libpng code. The library now has mechanisms for storing
|
|
|
3242 |
and writing chunks of unknown type; you can even declare callbacks
|
|
|
3243 |
for custom chunks. Hoewver, this may not be good enough if the
|
|
|
3244 |
library code itself needs to know about interactions between your
|
|
|
3245 |
chunk and existing `intrinsic' chunks.
|
|
|
3246 |
|
|
|
3247 |
If you need to write a new intrinsic chunk, first read the PNG
|
|
|
3248 |
specification. Acquire a first level of
|
|
|
3249 |
understanding of how it works. Pay particular attention to the
|
|
|
3250 |
sections that describe chunk names, and look at how other chunks were
|
|
|
3251 |
designed, so you can do things similarly. Second, check out the
|
|
|
3252 |
sections of libpng that read and write chunks. Try to find a chunk
|
|
|
3253 |
that is similar to yours and use it as a template. More details can
|
|
|
3254 |
be found in the comments inside the code. It is best to handle unknown
|
|
|
3255 |
chunks in a generic method, via callback functions, instead of by
|
|
|
3256 |
modifying libpng functions.
|
|
|
3257 |
|
|
|
3258 |
If you wish to write your own transformation for the data, look through
|
|
|
3259 |
the part of the code that does the transformations, and check out some of
|
|
|
3260 |
the simpler ones to get an idea of how they work. Try to find a similar
|
|
|
3261 |
transformation to the one you want to add and copy off of it. More details
|
|
|
3262 |
can be found in the comments inside the code itself.
|
|
|
3263 |
|
|
|
3264 |
.SS Configuring for 16 bit platforms
|
|
|
3265 |
|
|
|
3266 |
You will want to look into zconf.h to tell zlib (and thus libpng) that
|
|
|
3267 |
it cannot allocate more then 64K at a time. Even if you can, the memory
|
|
|
3268 |
won't be accessible. So limit zlib and libpng to 64K by defining MAXSEG_64K.
|
|
|
3269 |
|
|
|
3270 |
.SS Configuring for DOS
|
|
|
3271 |
|
|
|
3272 |
For DOS users who only have access to the lower 640K, you will
|
|
|
3273 |
have to limit zlib's memory usage via a png_set_compression_mem_level()
|
|
|
3274 |
call. See zlib.h or zconf.h in the zlib library for more information.
|
|
|
3275 |
|
|
|
3276 |
.SS Configuring for Medium Model
|
|
|
3277 |
|
|
|
3278 |
Libpng's support for medium model has been tested on most of the popular
|
|
|
3279 |
compilers. Make sure MAXSEG_64K gets defined, USE_FAR_KEYWORD gets
|
|
|
3280 |
defined, and FAR gets defined to far in pngconf.h, and you should be
|
|
|
3281 |
all set. Everything in the library (except for zlib's structure) is
|
|
|
3282 |
expecting far data. You must use the typedefs with the p or pp on
|
|
|
3283 |
the end for pointers (or at least look at them and be careful). Make
|
|
|
3284 |
note that the rows of data are defined as png_bytepp, which is an
|
|
|
3285 |
unsigned char far * far *.
|
|
|
3286 |
|
|
|
3287 |
.SS Configuring for gui/windowing platforms:
|
|
|
3288 |
|
|
|
3289 |
You will need to write new error and warning functions that use the GUI
|
|
|
3290 |
interface, as described previously, and set them to be the error and
|
|
|
3291 |
warning functions at the time that png_create_*_struct() is called,
|
|
|
3292 |
in order to have them available during the structure initialization.
|
|
|
3293 |
They can be changed later via png_set_error_fn(). On some compilers,
|
|
|
3294 |
you may also have to change the memory allocators (png_malloc, etc.).
|
|
|
3295 |
|
|
|
3296 |
.SS Configuring for compiler xxx:
|
|
|
3297 |
|
|
|
3298 |
All includes for libpng are in pngconf.h. If you need to add/change/delete
|
|
|
3299 |
an include, this is the place to do it. The includes that are not
|
|
|
3300 |
needed outside libpng are protected by the PNG_INTERNAL definition,
|
|
|
3301 |
which is only defined for those routines inside libpng itself. The
|
|
|
3302 |
files in libpng proper only include png.h, which includes pngconf.h.
|
|
|
3303 |
|
|
|
3304 |
.SS Configuring zlib:
|
|
|
3305 |
|
|
|
3306 |
There are special functions to configure the compression. Perhaps the
|
|
|
3307 |
most useful one changes the compression level, which currently uses
|
|
|
3308 |
input compression values in the range 0 - 9. The library normally
|
|
|
3309 |
uses the default compression level (Z_DEFAULT_COMPRESSION = 6). Tests
|
|
|
3310 |
have shown that for a large majority of images, compression values in
|
|
|
3311 |
the range 3-6 compress nearly as well as higher levels, and do so much
|
|
|
3312 |
faster. For online applications it may be desirable to have maximum speed
|
|
|
3313 |
(Z_BEST_SPEED = 1). With versions of zlib after v0.99, you can also
|
|
|
3314 |
specify no compression (Z_NO_COMPRESSION = 0), but this would create
|
|
|
3315 |
files larger than just storing the raw bitmap. You can specify the
|
|
|
3316 |
compression level by calling:
|
|
|
3317 |
|
|
|
3318 |
png_set_compression_level(png_ptr, level);
|
|
|
3319 |
|
|
|
3320 |
Another useful one is to reduce the memory level used by the library.
|
|
|
3321 |
The memory level defaults to 8, but it can be lowered if you are
|
|
|
3322 |
short on memory (running DOS, for example, where you only have 640K).
|
|
|
3323 |
Note that the memory level does have an effect on compression; among
|
|
|
3324 |
other things, lower levels will result in sections of incompressible
|
|
|
3325 |
data being emitted in smaller stored blocks, with a correspondingly
|
|
|
3326 |
larger relative overhead of up to 15% in the worst case.
|
|
|
3327 |
|
|
|
3328 |
png_set_compression_mem_level(png_ptr, level);
|
|
|
3329 |
|
|
|
3330 |
The other functions are for configuring zlib. They are not recommended
|
|
|
3331 |
for normal use and may result in writing an invalid PNG file. See
|
|
|
3332 |
zlib.h for more information on what these mean.
|
|
|
3333 |
|
|
|
3334 |
png_set_compression_strategy(png_ptr,
|
|
|
3335 |
strategy);
|
|
|
3336 |
png_set_compression_window_bits(png_ptr,
|
|
|
3337 |
window_bits);
|
|
|
3338 |
png_set_compression_method(png_ptr, method);
|
|
|
3339 |
png_set_compression_buffer_size(png_ptr, size);
|
|
|
3340 |
|
|
|
3341 |
.SS Controlling row filtering
|
|
|
3342 |
|
|
|
3343 |
If you want to control whether libpng uses filtering or not, which
|
|
|
3344 |
filters are used, and how it goes about picking row filters, you
|
|
|
3345 |
can call one of these functions. The selection and configuration
|
|
|
3346 |
of row filters can have a significant impact on the size and
|
|
|
3347 |
encoding speed and a somewhat lesser impact on the decoding speed
|
|
|
3348 |
of an image. Filtering is enabled by default for RGB and grayscale
|
|
|
3349 |
images (with and without alpha), but not for paletted images nor
|
|
|
3350 |
for any images with bit depths less than 8 bits/pixel.
|
|
|
3351 |
|
|
|
3352 |
The 'method' parameter sets the main filtering method, which is
|
|
|
3353 |
currently only '0' in the PNG 1.2 specification. The 'filters'
|
|
|
3354 |
parameter sets which filter(s), if any, should be used for each
|
|
|
3355 |
scanline. Possible values are PNG_ALL_FILTERS and PNG_NO_FILTERS
|
|
|
3356 |
to turn filtering on and off, respectively.
|
|
|
3357 |
|
|
|
3358 |
Individual filter types are PNG_FILTER_NONE, PNG_FILTER_SUB,
|
|
|
3359 |
PNG_FILTER_UP, PNG_FILTER_AVG, PNG_FILTER_PAETH, which can be bitwise
|
|
|
3360 |
ORed together with '|' to specify one or more filters to use.
|
|
|
3361 |
These filters are described in more detail in the PNG specification.
|
|
|
3362 |
If you intend to change the filter type during the course of writing
|
|
|
3363 |
the image, you should start with flags set for all of the filters
|
|
|
3364 |
you intend to use so that libpng can initialize its internal
|
|
|
3365 |
structures appropriately for all of the filter types. (Note that this
|
|
|
3366 |
means the first row must always be adaptively filtered, because libpng
|
|
|
3367 |
currently does not allocate the filter buffers until png_write_row()
|
|
|
3368 |
is called for the first time.)
|
|
|
3369 |
|
|
|
3370 |
filters = PNG_FILTER_NONE | PNG_FILTER_SUB
|
|
|
3371 |
PNG_FILTER_UP | PNG_FILTER_AVE |
|
|
|
3372 |
PNG_FILTER_PAETH | PNG_ALL_FILTERS;
|
|
|
3373 |
|
|
|
3374 |
png_set_filter(png_ptr, PNG_FILTER_TYPE_BASE,
|
|
|
3375 |
filters);
|
|
|
3376 |
The second parameter can also be
|
|
|
3377 |
PNG_INTRAPIXEL_DIFFERENCING if you are
|
|
|
3378 |
writing a PNG to be embedded in a MNG
|
|
|
3379 |
datastream. This parameter must be the
|
|
|
3380 |
same as the value of filter_method used
|
|
|
3381 |
in png_set_IHDR().
|
|
|
3382 |
|
|
|
3383 |
It is also possible to influence how libpng chooses from among the
|
|
|
3384 |
available filters. This is done in one or both of two ways - by
|
|
|
3385 |
telling it how important it is to keep the same filter for successive
|
|
|
3386 |
rows, and by telling it the relative computational costs of the filters.
|
|
|
3387 |
|
|
|
3388 |
double weights[3] = {1.5, 1.3, 1.1},
|
|
|
3389 |
costs[PNG_FILTER_VALUE_LAST] =
|
|
|
3390 |
{1.0, 1.3, 1.3, 1.5, 1.7};
|
|
|
3391 |
|
|
|
3392 |
png_set_filter_heuristics(png_ptr,
|
|
|
3393 |
PNG_FILTER_HEURISTIC_WEIGHTED, 3,
|
|
|
3394 |
weights, costs);
|
|
|
3395 |
|
|
|
3396 |
The weights are multiplying factors that indicate to libpng that the
|
|
|
3397 |
row filter should be the same for successive rows unless another row filter
|
|
|
3398 |
is that many times better than the previous filter. In the above example,
|
|
|
3399 |
if the previous 3 filters were SUB, SUB, NONE, the SUB filter could have a
|
|
|
3400 |
"sum of absolute differences" 1.5 x 1.3 times higher than other filters
|
|
|
3401 |
and still be chosen, while the NONE filter could have a sum 1.1 times
|
|
|
3402 |
higher than other filters and still be chosen. Unspecified weights are
|
|
|
3403 |
taken to be 1.0, and the specified weights should probably be declining
|
|
|
3404 |
like those above in order to emphasize recent filters over older filters.
|
|
|
3405 |
|
|
|
3406 |
The filter costs specify for each filter type a relative decoding cost
|
|
|
3407 |
to be considered when selecting row filters. This means that filters
|
|
|
3408 |
with higher costs are less likely to be chosen over filters with lower
|
|
|
3409 |
costs, unless their "sum of absolute differences" is that much smaller.
|
|
|
3410 |
The costs do not necessarily reflect the exact computational speeds of
|
|
|
3411 |
the various filters, since this would unduly influence the final image
|
|
|
3412 |
size.
|
|
|
3413 |
|
|
|
3414 |
Note that the numbers above were invented purely for this example and
|
|
|
3415 |
are given only to help explain the function usage. Little testing has
|
|
|
3416 |
been done to find optimum values for either the costs or the weights.
|
|
|
3417 |
|
|
|
3418 |
.SS Removing unwanted object code
|
|
|
3419 |
|
|
|
3420 |
There are a bunch of #define's in pngconf.h that control what parts of
|
|
|
3421 |
libpng are compiled. All the defines end in _SUPPORTED. If you are
|
|
|
3422 |
never going to use a capability, you can change the #define to #undef
|
|
|
3423 |
before recompiling libpng and save yourself code and data space, or
|
|
|
3424 |
you can turn off individual capabilities with defines that begin with
|
|
|
3425 |
PNG_NO_.
|
|
|
3426 |
|
|
|
3427 |
You can also turn all of the transforms and ancillary chunk capabilities
|
|
|
3428 |
off en masse with compiler directives that define
|
|
|
3429 |
PNG_NO_READ[or WRITE]_TRANSFORMS, or PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS,
|
|
|
3430 |
or all four,
|
|
|
3431 |
along with directives to turn on any of the capabilities that you do
|
|
|
3432 |
want. The PNG_NO_READ[or WRITE]_TRANSFORMS directives disable
|
|
|
3433 |
the extra transformations but still leave the library fully capable of reading
|
|
|
3434 |
and writing PNG files with all known public chunks
|
|
|
3435 |
Use of the PNG_NO_READ[or WRITE]_ANCILLARY_CHUNKS directive
|
|
|
3436 |
produces a library that is incapable of reading or writing ancillary chunks.
|
|
|
3437 |
If you are not using the progressive reading capability, you can
|
|
|
3438 |
turn that off with PNG_NO_PROGRESSIVE_READ (don't confuse
|
|
|
3439 |
this with the INTERLACING capability, which you'll still have).
|
|
|
3440 |
|
|
|
3441 |
All the reading and writing specific code are in separate files, so the
|
|
|
3442 |
linker should only grab the files it needs. However, if you want to
|
|
|
3443 |
make sure, or if you are building a stand alone library, all the
|
|
|
3444 |
reading files start with pngr and all the writing files start with
|
|
|
3445 |
pngw. The files that don't match either (like png.c, pngtrans.c, etc.)
|
|
|
3446 |
are used for both reading and writing, and always need to be included.
|
|
|
3447 |
The progressive reader is in pngpread.c
|
|
|
3448 |
|
|
|
3449 |
If you are creating or distributing a dynamically linked library (a .so
|
|
|
3450 |
or DLL file), you should not remove or disable any parts of the library,
|
|
|
3451 |
as this will cause applications linked with different versions of the
|
|
|
3452 |
library to fail if they call functions not available in your library.
|
|
|
3453 |
The size of the library itself should not be an issue, because only
|
|
|
3454 |
those sections that are actually used will be loaded into memory.
|
|
|
3455 |
|
|
|
3456 |
.SS Requesting debug printout
|
|
|
3457 |
|
|
|
3458 |
The macro definition PNG_DEBUG can be used to request debugging
|
|
|
3459 |
printout. Set it to an integer value in the range 0 to 3. Higher
|
|
|
3460 |
numbers result in increasing amounts of debugging information. The
|
|
|
3461 |
information is printed to the "stderr" file, unless another file
|
|
|
3462 |
name is specified in the PNG_DEBUG_FILE macro definition.
|
|
|
3463 |
|
|
|
3464 |
When PNG_DEBUG > 0, the following functions (macros) become available:
|
|
|
3465 |
|
|
|
3466 |
png_debug(level, message)
|
|
|
3467 |
png_debug1(level, message, p1)
|
|
|
3468 |
png_debug2(level, message, p1, p2)
|
|
|
3469 |
|
|
|
3470 |
in which "level" is compared to PNG_DEBUG to decide whether to print
|
|
|
3471 |
the message, "message" is the formatted string to be printed,
|
|
|
3472 |
and p1 and p2 are parameters that are to be embedded in the string
|
|
|
3473 |
according to printf-style formatting directives. For example,
|
|
|
3474 |
|
|
|
3475 |
png_debug1(2, "foo=%d\n", foo);
|
|
|
3476 |
|
|
|
3477 |
is expanded to
|
|
|
3478 |
|
|
|
3479 |
if(PNG_DEBUG > 2)
|
|
|
3480 |
fprintf(PNG_DEBUG_FILE, "foo=%d\n", foo);
|
|
|
3481 |
|
|
|
3482 |
When PNG_DEBUG is defined but is zero, the macros aren't defined, but you
|
|
|
3483 |
can still use PNG_DEBUG to control your own debugging:
|
|
|
3484 |
|
|
|
3485 |
#ifdef PNG_DEBUG
|
|
|
3486 |
fprintf(stderr, ...
|
|
|
3487 |
#endif
|
|
|
3488 |
|
|
|
3489 |
When PNG_DEBUG = 1, the macros are defined, but only png_debug statements
|
|
|
3490 |
having level = 0 will be printed. There aren't any such statements in
|
|
|
3491 |
this version of libpng, but if you insert some they will be printed.
|
|
|
3492 |
|
|
|
3493 |
.SH VI. Runtime optimization
|
|
|
3494 |
|
|
|
3495 |
A new feature in libpng 1.2.0 is the ability to dynamically switch between
|
|
|
3496 |
standard and optimized versions of some routines. Currently these are
|
|
|
3497 |
limited to three computationally intensive tasks when reading PNG files:
|
|
|
3498 |
decoding row filters, expanding interlacing, and combining interlaced or
|
|
|
3499 |
transparent row data with previous row data. Currently the optimized
|
|
|
3500 |
versions are available only for x86 (Intel, AMD, etc.) platforms with
|
|
|
3501 |
MMX support, though this may change in future versions. (For example,
|
|
|
3502 |
the non-MMX assembler optimizations for zlib might become similarly
|
|
|
3503 |
runtime-selectable in future releases, in which case libpng could be
|
|
|
3504 |
extended to support them. Alternatively, the compile-time choice of
|
|
|
3505 |
floating-point versus integer routines for gamma correction might become
|
|
|
3506 |
runtime-selectable.)
|
|
|
3507 |
|
|
|
3508 |
Because such optimizations tend to be very platform- and compiler-dependent,
|
|
|
3509 |
both in how they are written and in how they perform, the new runtime code
|
|
|
3510 |
in libpng has been written to allow programs to query, enable, and disable
|
|
|
3511 |
either specific optimizations or all such optimizations. For example, to
|
|
|
3512 |
enable all possible optimizations (bearing in mind that some "optimizations"
|
|
|
3513 |
may actually run more slowly in rare cases):
|
|
|
3514 |
|
|
|
3515 |
#if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
|
|
|
3516 |
png_uint_32 mask, flags;
|
|
|
3517 |
|
|
|
3518 |
flags = png_get_asm_flags(png_ptr);
|
|
|
3519 |
mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
|
|
|
3520 |
png_set_asm_flags(png_ptr, flags | mask);
|
|
|
3521 |
#endif
|
|
|
3522 |
|
|
|
3523 |
To enable only optimizations relevant to reading PNGs, use PNG_SELECT_READ
|
|
|
3524 |
by itself when calling png_get_asm_flagmask(); similarly for optimizing
|
|
|
3525 |
only writing. To disable all optimizations:
|
|
|
3526 |
|
|
|
3527 |
#if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
|
|
|
3528 |
flags = png_get_asm_flags(png_ptr);
|
|
|
3529 |
mask = png_get_asm_flagmask(PNG_SELECT_READ | PNG_SELECT_WRITE);
|
|
|
3530 |
png_set_asm_flags(png_ptr, flags & ~mask);
|
|
|
3531 |
#endif
|
|
|
3532 |
|
|
|
3533 |
To enable or disable only MMX-related features, use png_get_mmx_flagmask()
|
|
|
3534 |
in place of png_get_asm_flagmask(). The mmx version takes one additional
|
|
|
3535 |
parameter:
|
|
|
3536 |
|
|
|
3537 |
#if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
|
|
|
3538 |
int selection = PNG_SELECT_READ | PNG_SELECT_WRITE;
|
|
|
3539 |
int compilerID;
|
|
|
3540 |
|
|
|
3541 |
mask = png_get_mmx_flagmask(selection, &compilerID);
|
|
|
3542 |
#endif
|
|
|
3543 |
|
|
|
3544 |
On return, compilerID will indicate which version of the MMX assembler
|
|
|
3545 |
optimizations was compiled. Currently two flavors exist: Microsoft
|
|
|
3546 |
Visual C++ (compilerID == 1) and GNU C (a.k.a. gcc/gas, compilerID == 2).
|
|
|
3547 |
On non-x86 platforms or on systems compiled without MMX optimizations, a
|
|
|
3548 |
value of -1 is used.
|
|
|
3549 |
|
|
|
3550 |
Note that both png_get_asm_flagmask() and png_get_mmx_flagmask() return
|
|
|
3551 |
all valid, settable optimization bits for the version of the library that's
|
|
|
3552 |
currently in use. In the case of shared (dynamically linked) libraries,
|
|
|
3553 |
this may include optimizations that did not exist at the time the code was
|
|
|
3554 |
written and compiled. It is also possible, of course, to enable only known,
|
|
|
3555 |
specific optimizations; for example:
|
|
|
3556 |
|
|
|
3557 |
#if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
|
|
|
3558 |
flags = PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
|
|
|
3559 |
| PNG_ASM_FLAG_MMX_READ_INTERLACE \
|
|
|
3560 |
| PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
|
|
|
3561 |
| PNG_ASM_FLAG_MMX_READ_FILTER_UP \
|
|
|
3562 |
| PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
|
|
|
3563 |
| PNG_ASM_FLAG_MMX_READ_FILTER_PAETH ;
|
|
|
3564 |
png_set_asm_flags(png_ptr, flags);
|
|
|
3565 |
#endif
|
|
|
3566 |
|
|
|
3567 |
This method would enable only the MMX read-optimizations available at the
|
|
|
3568 |
time of libpng 1.2.0's release, regardless of whether a later version of
|
|
|
3569 |
the DLL were actually being used. (Also note that these functions did not
|
|
|
3570 |
exist in versions older than 1.2.0, so any attempt to run a dynamically
|
|
|
3571 |
linked app on such an older version would fail.)
|
|
|
3572 |
|
|
|
3573 |
To determine whether the processor supports MMX instructions at all, use
|
|
|
3574 |
the png_mmx_support() function:
|
|
|
3575 |
|
|
|
3576 |
#if defined(PNG_LIBPNG_VER) && (PNG_LIBPNG_VER >= 10200)
|
|
|
3577 |
mmxsupport = png_mmx_support();
|
|
|
3578 |
#endif
|
|
|
3579 |
|
|
|
3580 |
It returns -1 if MMX support is not compiled into libpng, 0 if MMX code
|
|
|
3581 |
is compiled but MMX is not supported by the processor, or 1 if MMX support
|
|
|
3582 |
is fully available. Note that png_mmx_support(), png_get_mmx_flagmask(),
|
|
|
3583 |
and png_get_asm_flagmask() all may be called without allocating and ini-
|
|
|
3584 |
tializing any PNG structures (for example, as part of a usage screen or
|
|
|
3585 |
"about" box).
|
|
|
3586 |
|
|
|
3587 |
The following code can be used to prevent an application from using the
|
|
|
3588 |
thread_unsafe features, even if libpng was built with PNG_THREAD_UNSAFE_OK
|
|
|
3589 |
defined:
|
|
|
3590 |
|
|
|
3591 |
#if defined(PNG_USE_PNGGCCRD) && defined(PNG_ASSEMBLER_CODE_SUPPORTED) \
|
|
|
3592 |
&& defined(PNG_THREAD_UNSAFE_OK)
|
|
|
3593 |
/* Disable thread-unsafe features of pnggccrd */
|
|
|
3594 |
if (png_access_version() >= 10200)
|
|
|
3595 |
{
|
|
|
3596 |
png_uint_32 mmx_disable_mask = 0;
|
|
|
3597 |
png_uint_32 asm_flags;
|
|
|
3598 |
|
|
|
3599 |
mmx_disable_mask |= ( PNG_ASM_FLAG_MMX_READ_COMBINE_ROW \
|
|
|
3600 |
| PNG_ASM_FLAG_MMX_READ_FILTER_SUB \
|
|
|
3601 |
| PNG_ASM_FLAG_MMX_READ_FILTER_AVG \
|
|
|
3602 |
| PNG_ASM_FLAG_MMX_READ_FILTER_PAETH );
|
|
|
3603 |
asm_flags = png_get_asm_flags(png_ptr);
|
|
|
3604 |
png_set_asm_flags(png_ptr, asm_flags & ~mmx_disable_mask);
|
|
|
3605 |
}
|
|
|
3606 |
#endif
|
|
|
3607 |
|
|
|
3608 |
For more extensive examples of runtime querying, enabling and disabling
|
|
|
3609 |
of optimized features, see contrib/gregbook/readpng2.c in the libpng
|
|
|
3610 |
source-code distribution.
|
|
|
3611 |
|
|
|
3612 |
.SH VII. MNG support
|
|
|
3613 |
|
|
|
3614 |
The MNG specification (available at http://www.libpng.org/pub/mng) allows
|
|
|
3615 |
certain extensions to PNG for PNG images that are embedded in MNG datastreams.
|
|
|
3616 |
Libpng can support some of these extensions. To enable them, use the
|
|
|
3617 |
png_permit_mng_features() function:
|
|
|
3618 |
|
|
|
3619 |
feature_set = png_permit_mng_features(png_ptr, mask)
|
|
|
3620 |
mask is a png_uint_32 containing the logical OR of the
|
|
|
3621 |
features you want to enable. These include
|
|
|
3622 |
PNG_FLAG_MNG_EMPTY_PLTE
|
|
|
3623 |
PNG_FLAG_MNG_FILTER_64
|
|
|
3624 |
PNG_ALL_MNG_FEATURES
|
|
|
3625 |
feature_set is a png_uint_32 that is the logical AND of
|
|
|
3626 |
your mask with the set of MNG features that is
|
|
|
3627 |
supported by the version of libpng that you are using.
|
|
|
3628 |
|
|
|
3629 |
It is an error to use this function when reading or writing a standalone
|
|
|
3630 |
PNG file with the PNG 8-byte signature. The PNG datastream must be wrapped
|
|
|
3631 |
in a MNG datastream. As a minimum, it must have the MNG 8-byte signature
|
|
|
3632 |
and the MHDR and MEND chunks. Libpng does not provide support for these
|
|
|
3633 |
or any other MNG chunks; your application must provide its own support for
|
|
|
3634 |
them. You may wish to consider using libmng (available at
|
|
|
3635 |
http://www.libmng.com) instead.
|
|
|
3636 |
|
|
|
3637 |
.SH VIII. Changes to Libpng from version 0.88
|
|
|
3638 |
|
|
|
3639 |
It should be noted that versions of libpng later than 0.96 are not
|
|
|
3640 |
distributed by the original libpng author, Guy Schalnat, nor by
|
|
|
3641 |
Andreas Dilger, who had taken over from Guy during 1996 and 1997, and
|
|
|
3642 |
distributed versions 0.89 through 0.96, but rather by another member
|
|
|
3643 |
of the original PNG Group, Glenn Randers-Pehrson. Guy and Andreas are
|
|
|
3644 |
still alive and well, but they have moved on to other things.
|
|
|
3645 |
|
|
|
3646 |
The old libpng functions png_read_init(), png_write_init(),
|
|
|
3647 |
png_info_init(), png_read_destroy(), and png_write_destroy() have been
|
|
|
3648 |
moved to PNG_INTERNAL in version 0.95 to discourage their use. These
|
|
|
3649 |
functions will be removed from libpng version 2.0.0.
|
|
|
3650 |
|
|
|
3651 |
The preferred method of creating and initializing the libpng structures is
|
|
|
3652 |
via the png_create_read_struct(), png_create_write_struct(), and
|
|
|
3653 |
png_create_info_struct() because they isolate the size of the structures
|
|
|
3654 |
from the application, allow version error checking, and also allow the
|
|
|
3655 |
use of custom error handling routines during the initialization, which
|
|
|
3656 |
the old functions do not. The functions png_read_destroy() and
|
|
|
3657 |
png_write_destroy() do not actually free the memory that libpng
|
|
|
3658 |
allocated for these structs, but just reset the data structures, so they
|
|
|
3659 |
can be used instead of png_destroy_read_struct() and
|
|
|
3660 |
png_destroy_write_struct() if you feel there is too much system overhead
|
|
|
3661 |
allocating and freeing the png_struct for each image read.
|
|
|
3662 |
|
|
|
3663 |
Setting the error callbacks via png_set_message_fn() before
|
|
|
3664 |
png_read_init() as was suggested in libpng-0.88 is no longer supported
|
|
|
3665 |
because this caused applications that do not use custom error functions
|
|
|
3666 |
to fail if the png_ptr was not initialized to zero. It is still possible
|
|
|
3667 |
to set the error callbacks AFTER png_read_init(), or to change them with
|
|
|
3668 |
png_set_error_fn(), which is essentially the same function, but with a new
|
|
|
3669 |
name to force compilation errors with applications that try to use the old
|
|
|
3670 |
method.
|
|
|
3671 |
|
|
|
3672 |
Starting with version 1.0.7, you can find out which version of the library
|
|
|
3673 |
you are using at run-time:
|
|
|
3674 |
|
|
|
3675 |
png_uint_32 libpng_vn = png_access_version_number();
|
|
|
3676 |
|
|
|
3677 |
The number libpng_vn is constructed from the major version, minor
|
|
|
3678 |
version with leading zero, and release number with leading zero,
|
|
|
3679 |
(e.g., libpng_vn for version 1.0.7 is 10007).
|
|
|
3680 |
|
|
|
3681 |
You can also check which version of png.h you used when compiling your
|
|
|
3682 |
application:
|
|
|
3683 |
|
|
|
3684 |
png_uint_32 application_vn = PNG_LIBPNG_VER;
|
|
|
3685 |
|
|
|
3686 |
.SH IX. Y2K Compliance in libpng
|
|
|
3687 |
|
|
|
3688 |
December 3, 2004
|
|
|
3689 |
|
|
|
3690 |
Since the PNG Development group is an ad-hoc body, we can't make
|
|
|
3691 |
an official declaration.
|
|
|
3692 |
|
|
|
3693 |
This is your unofficial assurance that libpng from version 0.71 and
|
|
|
3694 |
upward through 1.2.8 are Y2K compliant. It is my belief that earlier
|
|
|
3695 |
versions were also Y2K compliant.
|
|
|
3696 |
|
|
|
3697 |
Libpng only has three year fields. One is a 2-byte unsigned integer that
|
|
|
3698 |
will hold years up to 65535. The other two hold the date in text
|
|
|
3699 |
format, and will hold years up to 9999.
|
|
|
3700 |
|
|
|
3701 |
The integer is
|
|
|
3702 |
"png_uint_16 year" in png_time_struct.
|
|
|
3703 |
|
|
|
3704 |
The strings are
|
|
|
3705 |
"png_charp time_buffer" in png_struct and
|
|
|
3706 |
"near_time_buffer", which is a local character string in png.c.
|
|
|
3707 |
|
|
|
3708 |
There are seven time-related functions:
|
|
|
3709 |
|
|
|
3710 |
png_convert_to_rfc_1123() in png.c
|
|
|
3711 |
(formerly png_convert_to_rfc_1152() in error)
|
|
|
3712 |
png_convert_from_struct_tm() in pngwrite.c, called
|
|
|
3713 |
in pngwrite.c
|
|
|
3714 |
png_convert_from_time_t() in pngwrite.c
|
|
|
3715 |
png_get_tIME() in pngget.c
|
|
|
3716 |
png_handle_tIME() in pngrutil.c, called in pngread.c
|
|
|
3717 |
png_set_tIME() in pngset.c
|
|
|
3718 |
png_write_tIME() in pngwutil.c, called in pngwrite.c
|
|
|
3719 |
|
|
|
3720 |
All appear to handle dates properly in a Y2K environment. The
|
|
|
3721 |
png_convert_from_time_t() function calls gmtime() to convert from system
|
|
|
3722 |
clock time, which returns (year - 1900), which we properly convert to
|
|
|
3723 |
the full 4-digit year. There is a possibility that applications using
|
|
|
3724 |
libpng are not passing 4-digit years into the png_convert_to_rfc_1123()
|
|
|
3725 |
function, or that they are incorrectly passing only a 2-digit year
|
|
|
3726 |
instead of "year - 1900" into the png_convert_from_struct_tm() function,
|
|
|
3727 |
but this is not under our control. The libpng documentation has always
|
|
|
3728 |
stated that it works with 4-digit years, and the APIs have been
|
|
|
3729 |
documented as such.
|
|
|
3730 |
|
|
|
3731 |
The tIME chunk itself is also Y2K compliant. It uses a 2-byte unsigned
|
|
|
3732 |
integer to hold the year, and can hold years as large as 65535.
|
|
|
3733 |
|
|
|
3734 |
zlib, upon which libpng depends, is also Y2K compliant. It contains
|
|
|
3735 |
no date-related code.
|
|
|
3736 |
|
|
|
3737 |
|
|
|
3738 |
Glenn Randers-Pehrson
|
|
|
3739 |
libpng maintainer
|
|
|
3740 |
PNG Development Group
|
|
|
3741 |
|
|
|
3742 |
.SH NOTE
|
|
|
3743 |
|
|
|
3744 |
Note about libpng version numbers:
|
|
|
3745 |
|
|
|
3746 |
Due to various miscommunications, unforeseen code incompatibilities
|
|
|
3747 |
and occasional factors outside the authors' control, version numbering
|
|
|
3748 |
on the library has not always been consistent and straightforward.
|
|
|
3749 |
The following table summarizes matters since version 0.89c, which was
|
|
|
3750 |
the first widely used release:
|
|
|
3751 |
|
|
|
3752 |
source png.h png.h shared-lib
|
|
|
3753 |
version string int version
|
|
|
3754 |
------- ------ ----- ----------
|
|
|
3755 |
0.89c ("beta 3") 0.89 89 1.0.89
|
|
|
3756 |
0.90 ("beta 4") 0.90 90 0.90
|
|
|
3757 |
0.95 ("beta 5") 0.95 95 0.95
|
|
|
3758 |
0.96 ("beta 6") 0.96 96 0.96
|
|
|
3759 |
0.97b ("beta 7") 1.00.97 97 1.0.1
|
|
|
3760 |
0.97c 0.97 97 2.0.97
|
|
|
3761 |
0.98 0.98 98 2.0.98
|
|
|
3762 |
0.99 0.99 98 2.0.99
|
|
|
3763 |
0.99a-m 0.99 99 2.0.99
|
|
|
3764 |
1.00 1.00 100 2.1.0
|
|
|
3765 |
1.0.0 1.0.0 100 2.1.0
|
|
|
3766 |
1.0.0 (from here on, the 100 2.1.0
|
|
|
3767 |
1.0.1 png.h string is 10001 2.1.0
|
|
|
3768 |
1.0.1a-e identical to the 10002 from here on, the
|
|
|
3769 |
1.0.2 source version) 10002 shared library is 2.V
|
|
|
3770 |
1.0.2a-b 10003 where V is the source
|
|
|
3771 |
1.0.1 10001 code version except as
|
|
|
3772 |
1.0.1a-e 10002 2.1.0.1a-e noted.
|
|
|
3773 |
1.0.2 10002 2.1.0.2
|
|
|
3774 |
1.0.2a-b 10003 2.1.0.2a-b
|
|
|
3775 |
1.0.3 10003 2.1.0.3
|
|
|
3776 |
1.0.3a-d 10004 2.1.0.3a-d
|
|
|
3777 |
1.0.4 10004 2.1.0.4
|
|
|
3778 |
1.0.4a-f 10005 2.1.0.4a-f
|
|
|
3779 |
1.0.5 (+ 2 patches) 10005 2.1.0.5
|
|
|
3780 |
1.0.5a-d 10006 2.1.0.5a-d
|
|
|
3781 |
1.0.5e-r 10100 2.1.0.5e-r
|
|
|
3782 |
1.0.5s-v 10006 2.1.0.5s-v
|
|
|
3783 |
1.0.6 (+ 3 patches) 10006 2.1.0.6
|
|
|
3784 |
1.0.6d-g 10007 2.1.0.6d-g
|
|
|
3785 |
1.0.6h 10007 10.6h
|
|
|
3786 |
1.0.6i 10007 10.6i
|
|
|
3787 |
1.0.6j 10007 2.1.0.6j
|
|
|
3788 |
1.0.7beta11-14 DLLNUM 10007 2.1.0.7beta11-14
|
|
|
3789 |
1.0.7beta15-18 1 10007 2.1.0.7beta15-18
|
|
|
3790 |
1.0.7rc1-2 1 10007 2.1.0.7rc1-2
|
|
|
3791 |
1.0.7 1 10007 2.1.0.7
|
|
|
3792 |
1.0.8beta1-4 1 10008 2.1.0.8beta1-4
|
|
|
3793 |
1.0.8rc1 1 10008 2.1.0.8rc1
|
|
|
3794 |
1.0.8 1 10008 2.1.0.8
|
|
|
3795 |
1.0.9beta1-6 1 10009 2.1.0.9beta1-6
|
|
|
3796 |
1.0.9rc1 1 10009 2.1.0.9rc1
|
|
|
3797 |
1.0.9beta7-10 1 10009 2.1.0.9beta7-10
|
|
|
3798 |
1.0.9rc2 1 10009 2.1.0.9rc2
|
|
|
3799 |
1.0.9 1 10009 2.1.0.9
|
|
|
3800 |
1.0.10beta1 1 10010 2.1.0.10beta1
|
|
|
3801 |
1.0.10rc1 1 10010 2.1.0.10rc1
|
|
|
3802 |
1.0.10 1 10010 2.1.0.10
|
|
|
3803 |
1.0.11beta1-3 1 10011 2.1.0.11beta1-3
|
|
|
3804 |
1.0.11rc1 1 10011 2.1.0.11rc1
|
|
|
3805 |
1.0.11 1 10011 2.1.0.11
|
|
|
3806 |
1.0.12beta1-2 2 10012 2.1.0.12beta1-2
|
|
|
3807 |
1.0.12rc1 2 10012 2.1.0.12rc1
|
|
|
3808 |
1.0.12 2 10012 2.1.0.12
|
|
|
3809 |
1.1.0a-f - 10100 2.1.1.0a-f abandoned
|
|
|
3810 |
1.2.0beta1-2 2 10200 2.1.2.0beta1-2
|
|
|
3811 |
1.2.0beta3-5 3 10200 3.1.2.0beta3-5
|
|
|
3812 |
1.2.0rc1 3 10200 3.1.2.0rc1
|
|
|
3813 |
1.2.0 3 10200 3.1.2.0
|
|
|
3814 |
1.2.1beta-4 3 10201 3.1.2.1beta1-4
|
|
|
3815 |
1.2.1rc1-2 3 10201 3.1.2.1rc1-2
|
|
|
3816 |
1.2.1 3 10201 3.1.2.1
|
|
|
3817 |
1.2.2beta1-6 12 10202 12.so.0.1.2.2beta1-6
|
|
|
3818 |
1.0.13beta1 10 10013 10.so.0.1.0.13beta1
|
|
|
3819 |
1.0.13rc1 10 10013 10.so.0.1.0.13rc1
|
|
|
3820 |
1.2.2rc1 12 10202 12.so.0.1.2.2rc1
|
|
|
3821 |
1.0.13 10 10013 10.so.0.1.0.13
|
|
|
3822 |
1.2.2 12 10202 12.so.0.1.2.2
|
|
|
3823 |
1.2.3rc1-6 12 10203 12.so.0.1.2.3rc1-6
|
|
|
3824 |
1.2.3 12 10203 12.so.0.1.2.3
|
|
|
3825 |
1.2.4beta1-3 13 10204 12.so.0.1.2.4beta1-3
|
|
|
3826 |
1.2.4rc1 13 10204 12.so.0.1.2.4rc1
|
|
|
3827 |
1.0.14 10 10014 10.so.0.1.0.14
|
|
|
3828 |
1.2.4 13 10204 12.so.0.1.2.4
|
|
|
3829 |
1.2.5beta1-2 13 10205 12.so.0.1.2.5beta1-2
|
|
|
3830 |
1.0.15rc1 10 10015 10.so.0.1.0.15rc1
|
|
|
3831 |
1.0.15 10 10015 10.so.0.1.0.15
|
|
|
3832 |
1.2.5 13 10205 12.so.0.1.2.5
|
|
|
3833 |
1.2.6beta1-4 13 10206 12.so.0.1.2.6beta1-4
|
|
|
3834 |
1.2.6rc1-5 13 10206 12.so.0.1.2.6rc1-5
|
|
|
3835 |
1.0.16 10 10016 10.so.0.1.0.16
|
|
|
3836 |
1.2.6 13 10206 12.so.0.1.2.6
|
|
|
3837 |
1.2.7beta1-2 13 10207 12.so.0.1.2.7beta1-2
|
|
|
3838 |
1.0.17rc1 10 10017 12.so.0.1.0.17rc1
|
|
|
3839 |
1.2.7rc1 13 10207 12.so.0.1.2.7rc1
|
|
|
3840 |
1.0.17 10 10017 12.so.0.1.0.17
|
|
|
3841 |
1.2.7 13 10207 12.so.0.1.2.7
|
|
|
3842 |
1.2.8beta1-5 13 10208 12.so.0.1.2.8beta1-5
|
|
|
3843 |
1.0.18rc1-5 10 10018 12.so.0.1.0.18rc1-5
|
|
|
3844 |
1.2.8rc1-5 13 10208 12.so.0.1.2.8rc1-5
|
|
|
3845 |
1.0.18 10 10018 12.so.0.1.0.18
|
|
|
3846 |
1.2.8 13 10208 12.so.0.1.2.8
|
|
|
3847 |
|
|
|
3848 |
Henceforth the source version will match the shared-library minor
|
|
|
3849 |
and patch numbers; the shared-library major version number will be
|
|
|
3850 |
used for changes in backward compatibility, as it is intended. The
|
|
|
3851 |
PNG_PNGLIB_VER macro, which is not used within libpng but is available
|
|
|
3852 |
for applications, is an unsigned integer of the form xyyzz corresponding
|
|
|
3853 |
to the source version x.y.z (leading zeros in y and z). Beta versions
|
|
|
3854 |
were given the previous public release number plus a letter, until
|
|
|
3855 |
version 1.0.6j; from then on they were given the upcoming public
|
|
|
3856 |
release number plus "betaNN" or "rcN".
|
|
|
3857 |
|
|
|
3858 |
.SH "SEE ALSO"
|
|
|
3859 |
libpngpf(3), png(5)
|
|
|
3860 |
.LP
|
|
|
3861 |
.IR libpng :
|
|
|
3862 |
.IP
|
|
|
3863 |
http://libpng.sourceforge.net (follow the [DOWNLOAD] link)
|
|
|
3864 |
http://www.libpng.org/pub/png
|
|
|
3865 |
|
|
|
3866 |
.LP
|
|
|
3867 |
.IR zlib :
|
|
|
3868 |
.IP
|
|
|
3869 |
(generally) at the same location as
|
|
|
3870 |
.I libpng
|
|
|
3871 |
or at
|
|
|
3872 |
.br
|
|
|
3873 |
ftp://ftp.info-zip.org/pub/infozip/zlib
|
|
|
3874 |
|
|
|
3875 |
.LP
|
|
|
3876 |
.IR PNG specification: RFC 2083
|
|
|
3877 |
.IP
|
|
|
3878 |
(generally) at the same location as
|
|
|
3879 |
.I libpng
|
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|
3880 |
or at
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|
3881 |
.br
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|
3882 |
ftp://ds.internic.net/rfc/rfc2083.txt
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|
3883 |
.br
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|
3884 |
or (as a W3C Recommendation) at
|
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|
3885 |
.br
|
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|
3886 |
http://www.w3.org/TR/REC-png.html
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|
3887 |
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|
3888 |
.LP
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|
3889 |
In the case of any inconsistency between the PNG specification
|
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|
3890 |
and this library, the specification takes precedence.
|
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|
3891 |
|
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|
3892 |
.SH AUTHORS
|
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|
3893 |
This man page: Glenn Randers-Pehrson
|
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|
3894 |
<glennrp at users.sourceforge.net>
|
|
|
3895 |
|
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|
3896 |
The contributing authors would like to thank all those who helped
|
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|
3897 |
with testing, bug fixes, and patience. This wouldn't have been
|
|
|
3898 |
possible without all of you.
|
|
|
3899 |
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|
3900 |
Thanks to Frank J. T. Wojcik for helping with the documentation.
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|
3901 |
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|
3902 |
Libpng version 1.2.8 - December 3, 2004:
|
|
|
3903 |
Initially created in 1995 by Guy Eric Schalnat, then of Group 42, Inc.
|
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|
3904 |
Currently maintained by Glenn Randers-Pehrson (glennrp at users.sourceforge.net).
|
|
|
3905 |
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|
3906 |
Supported by the PNG development group
|
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|
3907 |
.br
|
|
|
3908 |
png-implement at ccrc.wustl.edu (subscription required; write to
|
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|
3909 |
majordomo at ccrc.wustl.edu with "subscribe png-implement" in the message).
|
|
|
3910 |
|
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|
3911 |
.SH COPYRIGHT NOTICE, DISCLAIMER, and LICENSE:
|
|
|
3912 |
|
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|
3913 |
(This copy of the libpng notices is provided for your convenience. In case of
|
|
|
3914 |
any discrepancy between this copy and the notices in the file png.h that is
|
|
|
3915 |
included in the libpng distribution, the latter shall prevail.)
|
|
|
3916 |
|
|
|
3917 |
If you modify libpng you may insert additional notices immediately following
|
|
|
3918 |
this sentence.
|
|
|
3919 |
|
|
|
3920 |
libpng version 1.2.6, December 3, 2004, is
|
|
|
3921 |
Copyright (c) 2004 Glenn Randers-Pehrson, and is
|
|
|
3922 |
distributed according to the same disclaimer and license as libpng-1.2.5
|
|
|
3923 |
with the following individual added to the list of Contributing Authors
|
|
|
3924 |
|
|
|
3925 |
Cosmin Truta
|
|
|
3926 |
|
|
|
3927 |
libpng versions 1.0.7, July 1, 2000, through 1.2.5 - October 3, 2002, are
|
|
|
3928 |
Copyright (c) 2000-2002 Glenn Randers-Pehrson, and are
|
|
|
3929 |
distributed according to the same disclaimer and license as libpng-1.0.6
|
|
|
3930 |
with the following individuals added to the list of Contributing Authors
|
|
|
3931 |
|
|
|
3932 |
Simon-Pierre Cadieux
|
|
|
3933 |
Eric S. Raymond
|
|
|
3934 |
Gilles Vollant
|
|
|
3935 |
|
|
|
3936 |
and with the following additions to the disclaimer:
|
|
|
3937 |
|
|
|
3938 |
There is no warranty against interference with your
|
|
|
3939 |
enjoyment of the library or against infringement.
|
|
|
3940 |
There is no warranty that our efforts or the library
|
|
|
3941 |
will fulfill any of your particular purposes or needs.
|
|
|
3942 |
This library is provided with all faults, and the entire
|
|
|
3943 |
risk of satisfactory quality, performance, accuracy, and
|
|
|
3944 |
effort is with the user.
|
|
|
3945 |
|
|
|
3946 |
libpng versions 0.97, January 1998, through 1.0.6, March 20, 2000, are
|
|
|
3947 |
Copyright (c) 1998, 1999 Glenn Randers-Pehrson
|
|
|
3948 |
Distributed according to the same disclaimer and license as libpng-0.96,
|
|
|
3949 |
with the following individuals added to the list of Contributing Authors:
|
|
|
3950 |
|
|
|
3951 |
Tom Lane
|
|
|
3952 |
Glenn Randers-Pehrson
|
|
|
3953 |
Willem van Schaik
|
|
|
3954 |
|
|
|
3955 |
libpng versions 0.89, June 1996, through 0.96, May 1997, are
|
|
|
3956 |
Copyright (c) 1996, 1997 Andreas Dilger
|
|
|
3957 |
Distributed according to the same disclaimer and license as libpng-0.88,
|
|
|
3958 |
with the following individuals added to the list of Contributing Authors:
|
|
|
3959 |
|
|
|
3960 |
John Bowler
|
|
|
3961 |
Kevin Bracey
|
|
|
3962 |
Sam Bushell
|
|
|
3963 |
Magnus Holmgren
|
|
|
3964 |
Greg Roelofs
|
|
|
3965 |
Tom Tanner
|
|
|
3966 |
|
|
|
3967 |
libpng versions 0.5, May 1995, through 0.88, January 1996, are
|
|
|
3968 |
Copyright (c) 1995, 1996 Guy Eric Schalnat, Group 42, Inc.
|
|
|
3969 |
|
|
|
3970 |
For the purposes of this copyright and license, "Contributing Authors"
|
|
|
3971 |
is defined as the following set of individuals:
|
|
|
3972 |
|
|
|
3973 |
Andreas Dilger
|
|
|
3974 |
Dave Martindale
|
|
|
3975 |
Guy Eric Schalnat
|
|
|
3976 |
Paul Schmidt
|
|
|
3977 |
Tim Wegner
|
|
|
3978 |
|
|
|
3979 |
The PNG Reference Library is supplied "AS IS". The Contributing Authors
|
|
|
3980 |
and Group 42, Inc. disclaim all warranties, expressed or implied,
|
|
|
3981 |
including, without limitation, the warranties of merchantability and of
|
|
|
3982 |
fitness for any purpose. The Contributing Authors and Group 42, Inc.
|
|
|
3983 |
assume no liability for direct, indirect, incidental, special, exemplary,
|
|
|
3984 |
or consequential damages, which may result from the use of the PNG
|
|
|
3985 |
Reference Library, even if advised of the possibility of such damage.
|
|
|
3986 |
|
|
|
3987 |
Permission is hereby granted to use, copy, modify, and distribute this
|
|
|
3988 |
source code, or portions hereof, for any purpose, without fee, subject
|
|
|
3989 |
to the following restrictions:
|
|
|
3990 |
|
|
|
3991 |
1. The origin of this source code must not be misrepresented.
|
|
|
3992 |
|
|
|
3993 |
2. Altered versions must be plainly marked as such and
|
|
|
3994 |
must not be misrepresented as being the original source.
|
|
|
3995 |
|
|
|
3996 |
3. This Copyright notice may not be removed or altered from
|
|
|
3997 |
any source or altered source distribution.
|
|
|
3998 |
|
|
|
3999 |
The Contributing Authors and Group 42, Inc. specifically permit, without
|
|
|
4000 |
fee, and encourage the use of this source code as a component to
|
|
|
4001 |
supporting the PNG file format in commercial products. If you use this
|
|
|
4002 |
source code in a product, acknowledgment is not required but would be
|
|
|
4003 |
appreciated.
|
|
|
4004 |
|
|
|
4005 |
|
|
|
4006 |
A "png_get_copyright" function is available, for convenient use in "about"
|
|
|
4007 |
boxes and the like:
|
|
|
4008 |
|
|
|
4009 |
printf("%s",png_get_copyright(NULL));
|
|
|
4010 |
|
|
|
4011 |
Also, the PNG logo (in PNG format, of course) is supplied in the
|
|
|
4012 |
files "pngbar.png" and "pngbar.jpg (88x31) and "pngnow.png" (98x31).
|
|
|
4013 |
|
|
|
4014 |
Libpng is OSI Certified Open Source Software. OSI Certified Open Source is a
|
|
|
4015 |
certification mark of the Open Source Initiative.
|
|
|
4016 |
|
|
|
4017 |
Glenn Randers-Pehrson
|
|
|
4018 |
glennrp at users.sourceforge.net
|
|
|
4019 |
December 3, 2004
|
|
|
4020 |
|
|
|
4021 |
.\" end of man page
|
|
|
4022 |
|