[RFC wayland-protocols v2 0/1] Color Management Protocol

Kai-Uwe ku.b-list at gmx.de
Fri Mar 15 13:48:44 UTC 2019

Am 15.03.19 um 11:41 schrieb Pekka Paalanen:
> Can an ICC file include a per-channel degamma and gamma LUTs? That
> is, in addition to the usual profile data that allows mapping between
> PCS and the device space.

Not in absolute terms. But most monitor 3D LUT profiles contain as well
TRC (tonal response curve) and a matrix. So that curves might be already
a good enough degamma. Otherwise use something reasonably, e.g. from
EDID gamma value or fall back to a default gamma of 2.2 .

> If yes, and if there are profiling applications that can produce those
> properly, maybe a compositor could check for the existence of the
> degamma/gamma LUTs and warn the user if they are missing? Up to
> compositor policy, of course.
The above gamma detection order can be used with any profile.
> Is extracting a degamma mapping from a LUT profile an ill-defined
> problem to begin with? If it can be done at all, I would be happy to
> punt that to color specialized tools producing ICC profiles and have
> compositors just say your output ICC profile file is lacking.
It is rather simple to extract the curves or white point. However, the
format might need adaption if the ICC curve format is not directly
implemented in the shaders.
> Especially so if finding the degamma mapping needs a measurement tool.

Measuring is too laborious and already expressed as the profile.

Kai-Uwe Behrmann

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