CGATS text file from a profile
CGATS text file from a profile
- Subject: CGATS text file from a profile
- From: Eric Nunn <email@hidden>
- Date: Thu, 17 Mar 2011 09:25:43 +0000
I'd like to ask a supplemental question on this if I may.
If I take the ISO newsprint profile - ISONewspaper26v4 - edit the whitepoint tag to reflect a Financial Times type paper colour, e.g. L81. a12. b22, I can "inject" the effect of that substrate across the whole colourspace but only if I use absolute rendering?
So when converting from RGB if I use relative colorimetric the edit I have made makes no difference, but if I do an absolute colorimetric conversion, I can in effect "subtract" the paper colour from the colourspace.
Have I understood this correctly?
Many thanks
Eric Nunn
> - Your question about white point editing is understandable. The reason it works is due to the nature of how ICC profiles are calculated. When profiling software generates the LUTs in a profile it "removes" the paper white from all the colors in the measurements file. As a result each tag (colorimetric, perceptual and saturation) has values that are all relative to "ideal white" (Lab = 100,0,0) and the only remaining evidence of the paper's original white value is in the profile's wtpt tag. This makes "normal" conversions easier as some of the heavy lifting has already been done. When you do an abs col transform (somewhat abnormal I guess), then the CMM reinserts the original white point from the wtpt tag. It's a bit of a messy affair and doesn't always work perfectly but it does leave us with the ability to simply edit a profile's white point in order to change all the colors in abs cols transforms!
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