[RFC wayland-protocols v2 1/1] Add the color-management protocol

[Pekka Paalanen]

On Mon, 4 Mar 2019 22:07:24 +1100
Graeme Gill <graeme2 at argyllcms.com> wrote:

> Pekka Paalanen wrote:
> 
> Hi,
> 
> > Does that even make any difference if the output space was linear at
> > blending step, and gamma was applied after that?  
> 
> as mentioned earlier, I think talk of using device links is now a red herring.
> 
> If it is desirable to do blending in a linear light space (as is typically
> the case), then this can be implemented in a way that leverages color management,
> without interfering with it. In a color managed workflow all color values intended
> for a particular output will be converted to that devices output space either
> by the client or the compositor on the clients behalf. The installed output device
> profile then can provide the necessary blending information. Even if
> a device colorspace is not terribly additive for the purposes of
> accurate profile creation, RGB devices are generally additive enough to
> approximate linear light mixing with per channel lookup curves. It's
> pretty straightforward to use the ICC profile to create such curves
> (for each of the RGB channels in turn with the others at zero, lookup
>  the Relative Colorimetric XYZ value and take the dot product with the
>  100% channel value. Ensure the curves are monotonic, and normalize them
>  to map 0 and 1 unchanged.)
> Compositing in a linear light space has to occur to sufficiently high
> precision of course, so as not to introduce quantization errors.
> After composition the inverse curves would be applied to return to the
> output device space.

Excellent!

Thank you,
pq
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