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ICC profile I/O library (icclib), README file

Date 2002/4/22, Version 2.02

This distribution contains source code which implements the reading and

writing of color profile files that conform to the International Color

Consortium (ICC) Profile Format Specification, Version 3.4.

For more information about the ICC, and for copies of the specification,

please refer to http://www.color.org/.

(Note that this software is written from the ICC V3.4 standard, but the

software and its author are not affiliated with, or otherwise connected

with the ICC.)

The ICC profile I/O library archive is kept at

http://web.access.net.au/argyll/color.html

(Version 2.02 is has a few minor changes and fixups from V2.00.

See icc.c for a more detailed change history.) 

Motivation

Color is still very much a black art to many programmers dealing with

computer graphics. The ICC Profile Format is an industry attempt to provide

an interchange format to help solve the problems of specifying color, and

in transferring color graphics from, and between systems and devices.

Although the ICC format has been around a number of years, and has long

been adopted by companies in the business of providing systems for

publishing and printing, and is now widely used as part of commercial

operating system support for device independent color, its uptake in the

general world of computer graphics has been slow.

The writing of this library was prompted by my private and professional

enthusiasm for computer graphics, and color. Inspired by other examples of

freely usable software (notably the Independent JPEG Group's free JPEG

software, and Sam Leffler's TIFF library), I have decided to make this

library available under similar terms.  I hope that this library will

provide a starting point for including ICC profile support more widely that

is currently the case, particularly in open source code projects.

Overview

This package contains a C software implementation of the ICC Profile

Format, Version 3.4. The ICC Profile Format attempts to provide a

cross-platform device profile format, that can be used to translate color

data created on one device into another device's native color space. For a

fuller explanation of what the ICC Profile Format is all about, please

refer to http://www.color.org, and the profile specification.

In summary this library provides:

   * Full source code, free for commercial and non-commercial use.

   * Support for all version 3.4 header elements, Tags and Tag Types.

   * Conversion to/from machine native representation of all data

     types.

   * Support for user defined Tags.

   * Support for adding/deleting Tags.

   * Support for Tag type sharing within a file (often used for

     sharing LUTs amongst intents).

   * Support for reading/writing embedded profiles, including

     from/to a memory buffer, rather than a file.

   * Provides a single function for transforming color values through

     a profile, including support for intents, forward and reverse

     transforms, gamut lookup or preview lookup.

   * Provides support and code examples for creating all profile

     types, monochrome, matrix and Lut.

   * Attempts to be platform neutral.

   * Loads Tag Types on demand to conserve memory space.

Changes from V1.30

 Change absolute conversion to be white point only, and use

 Bradford transform by default. (ie. we are now ignoring the

 comment in section 6.4.22 of the 1998 spec. about the

 media black point being used for absolute colorimetry,

 ignoring the recommendation on page 118 in section E.5,

 and are taking up the recommendation on page 124 in section

 E.16 that a more sophisticated chromatic adaption model be used.)

 This is for better compatibility with other CMM's, and to

 improve the results when using simple links between

 profiles with non-D50 white points. Standard profiles

 like sRGB will also be more accurate when interpreted

 with absolute colorimetric intent.

 This will cause some slight profile inaccuracy when used

 with profile created with previous versions of icclib.

 Added file I/O class to allow substitution of alternative ICC profile

 file access. Provide standard file class instance, and memory image

 instance of file I/O class as default and example. 

 Added an optional new_icc_a() object creator, that takes a memory

 allocator class instance. This allows an alternate memory heap to

 be used with the icc class. 

 Renamed object free() methods to del() for more consistency with new().

 Added ColorSync 2.5 specific VideoCardGamma tag support (from Neil Okamoto)

Package contents:

 icclib.zip ZIP archive of the following files

 README    This file.

 Licence.txt Important! - Permissions for use of this package.

 icc.c     Library source file.

 icc.h     Library include file. Note machine dependent defines. Includes

           icc9809.h.

 icc9809.h Lightly modified standard ICC header file.

 iccdump.c Program that dumps ASCII description of a profile.

 icclu.c   Program that allows interactive or batch translation of color

           values though a profile.

 icctest.c Basic library tag Read/Write example and regression test code.

 lutest.c  Color lookup regression test code, and example for creating

           color profiles.

 iccrw.c   Source code skeleton for reading and then re-writing a profile.

 jamfile   JAM style "makefile" see http://www.perforce.com/jam/jam.html

 makefile  UNIX style makefile. Modify this to suite your system.

Style

For handling convenience, I have included all the library source code in

two files. The down side is that they are both hard to read and navigate

through. The code could do with some cleaning up and rearrangement, to make

clear the distinction between public and private elements. (C++ would help

here, but is less portable.) The code attempts to be ANSI C compliant,

written in an object oriented style. Unfortunately, it has not been tested

on a wide variety of platforms, nor with a very wide set of color profiles,

so there my well be a number of bugs to discover. A tutorial on how to use

the library would also be a good thing !

The best way to learn how to use the library, is to take a look at

icctest.c, lutest.c and iccrw.c. The first is used to test writing and

reading to every type of element, with every possible variation of usage.

You will need a copy of the ICC spec. handy to understand what it all

means. The second source file specifically creates and then tests various

types of profiles, including monochrome, matrix and Lut style profiles. The

last is a source code skeleton, that reads a profile completely into

memory, and then writes it out again to a different file.

With the release of version 2.02 of icclib, the library is now as useful as

it is likely to be, allowing convenient color conversion between PCS

(profile connection spaces, either XYZ or Lab) and device specific color

spaces. The library does not attempt to be a complete color management

system however, lacking profile creation and linking functionality.

(The Argyll CMS provides full CMS functionality.)

I welcome feedback, positive or negative, so please mail me at

GraemeGill@access.net.au

Graeme Gill