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

Erwin Burema e.burema at gmail.com
Fri Mar 15 14:28:30 UTC 2019

On Fri, 15 Mar 2019 at 14:49, Kai-Uwe <ku.b-list at gmx.de> wrote:
> 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 .
This is mostly correct but there might still be some residue left for
example I pressent the curves from my (crappy)laptop screen

"degammaed" https://drive.google.com/open?id=1gS8F6ZXyfoobVWoHxD-IXM6_Hx7OJGCu
"gammaed" https://drive.google.com/open?id=1BpVG_Xvy0C4o9FBahseClFItyYeoz9zq

As you can see this is quite awe-full, no white balance, shift in
white balance over intensity, etc. It will be very hard to get this
linear and even then you will have white balance issues when blending
in this color space. Now would it be possible to get this close to
workable I have no idea but it will be kinda hard

> > 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.

But for cheap monitors (like a lot of laptop screens like mine) this
wouldn't be enough
> > 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.

That is true
> regards
> Kai-Uwe Behrmann

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