Marti Maria wrote:
Hi Marti,You say LCMS uses the rel.colorimetric CLUT (?) tables for the gamut warning. What do you do in case of matrix shaper profiles?It uses the only intent matrix-shaper has. It is already non clear if that is rel. colorimetric or (as I believe) perceptual. Think on matrix-shaper as a rel.colorimetric plus black point compensation.
according to table 20 on page 20 in the ICC.1:2001-12 spec (V4.0), it looks like matrix/TRC are supposed to describe the colorimetric intent, for input and display profiles. I've also checked the latest V2 spec (version 2.4.0) -- it sais the same, see table 20 in that spec too.
Tarlika,How would a profile have gamut remapping embedded?See above. Lab=(50, -120, -120) cannot be represented on the output device, so
the profile has to remap these out-on-gamut colors to whatever inside device space.
It cannot simply clip values since that would block all gradients from, say, Lab=(50, -40, -40) to Lab=(50, -120, -120). Gamut mapping is a hard subject and
that is what makes output profiles such difficult.
since your question was, *how* gamut remapping is embedded in the profile, I'd like to add:
It is done by the the BToA tables. The BToA1 table (relative colorimetric) is supposed to remap PCS values which are out-of-gamut on the device, to in-gamut device values. The BToA0 and BToA2 tables may even remap in-gamut colors, in order to achieve a "perceptually nice" result with smooth gradients, or strong, vivid colors (for BToA2 table). There are no particular rules given by the ICC spec, how the perceptual or saturation intent performs gamut remapping. To some extend this is rather art than science, and the only thing which counts is a pleasing result ...
Best Regards, Gerhard
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