[RFC wayland-protocols] Color management protocol

[Carsten Haitzler (The Rasterman)]

On Sun, 18 Dec 2016 16:25:13 +0100 Niels Ole Salscheider
<niels_ole at salscheider-online.de> said:

> I feel like the discussion drifts off a bit. You (Graeme) obviously know much 
> more about color management than I do. But as Pekka already pointed out there 
> are a few constraints that originate in the design decisions of wayland and 
> are quite different to these of X11. We can't change these constraints but 
> have to find a solution that works well with them:
> 
> - A normal application CANNOT control the hardware directly (it can't program 
> LUTs, for example).
> 
> - A normal application CANNOT alter global settings of the compositor (like 
> setting color profiles for the outputs). This can only be done by the 
> compositor or a few trusted applications. The user will just have to use the 
> settings dialog provided with the compositor. Because of that it does not 
> matter if this is implementation dependent.
> 
> - You DO NOT know which parts of a surface are shown on which screen.
> 
> - We aim to be pixel-perfect.
> 
> I think these constraints mean that we must let the compositor take part in 
> the color correction, at least if more than one screen is involved. If we do 
> so, we should also be able to expect that the compositor can handle a bit
> more complicated cases (e. g. an arbitrary number of different surfaces with 
> different color profiles).

bingo. and while we're at it we should solve our yuv colorspace issues too
(same as rgb. currently bt601, bt709 and bt2020 need supporting).

> When I proposed this protocol my focus was on applications that may not be 
> color managed currently. I thought for example about web browsers or simple 
> image viewers where I would view (but not edit) photos.
> Your focus is obviously on professional applications. I think both use cases 
> are equally important and we should not treat one as an afterthought of the 
> other.
> 
> I would be glad if we could come up with a solution that works for both under 
> these constraints.
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The Rasterman (Carsten Haitzler)    raster at rasterman.com