What are the LCh and JCh values for the sRGB blue primary?

[Elle (Elle Stone)]

@KelSolaar

There is no gamut mapping in the xicclu output when converting from a matrix sRGB ICC profile to Lab/LCh/etc. It just does the requested conversion using either relative or absolute colorimetric intent.

This is confusing, rendering intents are just about gamut mapping, could you or Graeme explain what is happening when you cherry-pick one or another?

Hmm, hopefully I’m not speaking too imprecisely here. But usually when people talk about gamut mapping they usually mean somehow shrinking the source color gamut to fit into the destination color space. This requires a destination ICC profile with lookup tables that tell how to map from the destination profile’s source color gamut (which might be an ICC profile, or the color gamut of a specific image, or etc) to the destination color space profile’s actual color gamut. In other words, you really are dealing with several different color gamuts here:

1. the color gamut of the original image encoded in whatever ICC profile color space.
2. the color gamut used as the source color gamut of the destination LUT profile - this determines how much “squeezing” is done by the LUT tables.
3. the color gamut of the destination “LUT” profile.

If the destination ICC profile is a matrix profile, then the “gamut mapping” is just clipping to the hull of the destination color space.

When using xicclu to convert from the ArgyllCMS sRGB.icm profile to XYZ and maybe then to LAB and to LCh, the entire sRGB color gamut fits inside the destination color space by definition. You can do the exact same calculations using a spreadsheet and get the same results. So unless the spreadsheet calculations are also “gamut mapping”, then there really isn’t any gamut mapping.