harvey/sys/src/cmd/gs/icclib

ICC profile I/O library (icclib), README file
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Date 99/11/29, Version 1.23

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

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.
* 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 V1.01

Major changes since version 1.01 are the addition of the profile color
lookup function, and Lut set_tables support function. The library has also
benefited from many minor bug fixes and enhancements. Special thanks to
Tsutomu Okuno and Yasuhiko Kiuchi for pointing out some subtle bugs in the
code, which I hope now are fixed.

Changes from V1.20

A minor change was made to Lab encoding and default scaling of Lut style
profiles, to bring it into line with recommended practice as described in
Michael Bourgoin's 1998 SIGGRAPH course notes. Only icc.c and lutest.c have
been altered.

Changes from V1.21

Some endian bugs in the Unicode read/write routines have been corrected, as
well as improving the codes portability to some older SUN systems. The
TextDescription dump() method now dumps Unicode and ScriptCode in Hex.
Simplex (i.e. tetrahedral in 3D) interpolation is now used where
appropriate for clut interpolation. The ICC.1:1998-09 include file is now
being used, but the DeviceSettings and OutputResponse tags are still not
supported.
Added more hooks to support inherited implimentation of color conversion,
used in Argyll to support reversing multi-dimentional table lookups.

Changes from V1.22

Fixed important bug in Lut read/write. The matrix values had their
rows and columns switched. Not many profiles exercise this code.
Thanks to David Gillman for discovering this.
Fixup compiler complains about illegal enum values for icmCurveStyle,
and icmDataStyle. Malloc memory icmLut_lookup_clut_nl for gw[], so that
it is more friendly to systems with a limited stack. (Thanks to Dave White)

Package contents:

icclib.zipZIP archive of the following files
README This file.
COPYRIGHT 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 1.23 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.

I welcome feedback, positive or negative, so please mail me at
GraemeGill@access.net.au

Graeme Gill