There are discrepancies when converting to an lcms built-in profile,
compared to converting to the same profile previously saved to disk.
I noticed the discrepancies while testing GIMP 2.9 16-bit integer and
32-bit floating point ICC profile conversions. The same discrepancies
happen when using tificc and also when using transicc. So the
discrepancies seems to be consistent across various ways of accessing
lcms built-in profiles.
Here is transicc output showing the discrepancies:
Converting to a copy of the lcms built-in sRGB profile that was
previously saved to disk ("-o sRGB-lcms-built-in.icc"):
$ transicc -w -t1 -c0 -b -i sRGB-elle-V4-g100.icc -o sRGB-lcms-built-in.icc
LittleCMS ColorSpace conversion calculator - 4.2 [LittleCMS 2.06]
Enter values, 'q' to quit
R? 255 255 255
G? B?
R=255.0019 G=254.9968 B=255.0028
Enter values, 'q' to quit
R? 255 0 0
G? B?
R=255.0450 G=0.0839 B=-0.0372
Enter values, 'q' to quit
R? 0 255 0
G? B?
R=-1.3516 G=254.9937 B=-0.3004
Enter values, 'q' to quit
R? 0 0 255
G? B?
R=0.0858 G=0.0080 B=255.0143
Converting to the transicc built-in sRGB profile ("-o *sRGB"):
$ transicc -w -t1 -c0 -b -i sRGB-elle-V4-g100.icc -o *sRGB
LittleCMS ColorSpace conversion calculator - 4.2 [LittleCMS 2.06]
Enter values, 'q' to quit
R? 255 255 255
G? B?
R=255.0007 G=254.9997 B=255.0009
Enter values, 'q' to quit
R? 255 0 0
G? B?
R=255.0428 G=0.1139 B=-0.0725
Enter values, 'q' to quit
R? 0 255 0
G? B?
R=-1.3259 G=254.9944 B=-0.2851
Enter values, 'q' to quit
R? 0 0 255
G? B?
R=0.0893 G=0.0423 B=255.0130
Here's the code that I used to save a copy of the lcms built-in sRGB
profile to disk:
After declaring/defining the variables:
profile = cmsCreate_sRGBProfile();
cmsWriteTag(profile, cmsSigCopyrightTag, copyright);
cmsWriteTag(profile, cmsSigDeviceMfgDescTag, manufacturer);
description = cmsMLUalloc(NULL, 1);
cmsMLUsetASCII(description, "en", "US", "sRGB-lcms-built-in.icc.");
cmsWriteTag(profile, cmsSigProfileDescriptionTag, description);
filename = "sRGB-lcms-built-in.icc";
cmsSaveProfileToFile(profile, filename);
cmsMLUfree(description);
Elle Stone
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