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

[Graeme Gill]

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.

Cheers,
	Graeme Gill.