COLOR TRANSFORMATION FILTERS
============================

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This software package contains EXAMPLES of lossless color transformation 
filters that can be used in conjunction with JPEG-LS, to improve
compression performance with certain color representations (e.g.,
some RGB images). 

THESE FILTERS ARE NOT PART OF THE JPEG-LS STANDARD. THEIR EFFECTIVENESS 
WILL DEPEND STRONGLY ON THE COLOR REPRESENTATION OF THE INPUT FILE.  
THEY ARE VERY SIMPLE, AND ARE NOT CLAIMED TO BE OPTIMAL OR RECOMMENDED 
FOR ANY SPECIFIC COLOR REPRESENTATION. 


Basically, the filter converts [X,Y,Z] triplets to [X-Y,Y,Z-Y]. For some
images, the latter representation is better decorrelated than the
original one, and yields better compression ratios, especially
in the [R,G,B] case. The trasformed images are of the same bit depth 
as the originals. An inverse filter is also provided.

THIS PACKAGE CONTAINS:
----------------------

	READCOLOR.TXT - this file
	ppm2pgmcf.exe, pgmcf2ppm.exe (Windows 95/98/NT executables)
	or
	ppm2pgmcf, pgmcf2ppm (HP-UX executables)
	subgold.ppm - a test image
	runtest.bat or runtest.sh - test script
	 
The test script assumes you have also downloaded the JPEG-LS software, and
that the JPEG-LS executables reside in the same directory as the color
filters and the test image.

All uncompressed images are assumed to be in PPM or PGM format (see the
README file in the JPEG-LS package).

Program: ppm2pgmcf  (color transformation)
-------------------------------------------

Converts [R,G,B] (1 PPM file) to [R-G,G,B-G] (3 PGM files).

Usage: ppm2pgmcf [-g<num>] infile [outprefix]

infile    : a PPM file
-g<num>   : what component is G (the "anchor"): 1,2,3,... (default num=2)
outprefix : prefix for output files (default: img, e.g. img1.pgm, img2.pgm,
	    img3.pgm)


Program: pgmcf2ppm (inverse color transformation)
--------------------------------------------------

Converts [R-G,G,B-G] (3 PGM files) to [R,G,B] (1 PPM file).

Usage: pgmcf2ppm [-g<num>] file1 file2 file3 [-ooutfile]

-g<num>   : what component is G: 1,2,3,... (default num=2)
file1, file2, file3: input PGM files.
outfile: Output PPM file (default: stdout)


Program: runtest (test script)
------------------------------
Runs the color transform on the test image, compresses with JPEG-LS,
decompresses, runs the inverse color transform.
To compare compression performance with "raw" JPEG-LS (no color transformation),
run
    locoe -N subgold.ppm


OTHER CAVEATS, LIMITATIONS, ANNOYANCES, BUGS (?)
=================================================
Same as with the JPEG-LS software (see README.TXT in that package).


Feedback to the LOCO-I/JPEG-LS team at HP Labs:
loco@hpl.hp.com