[RFC wayland-protocols] Add the color-management protocol

[Graeme Gill]

Daniel Stone wrote:

Hi,

> I mean lowest common denominator _between clients_, whilst still being
> tied to the output. So the gamut would ideally be as wide as (the
> specific output + highest gamut buffer being painted during this
> stage), but in taking multiple clients with potentially disparate
> colour source attributes and producing a single flat buffer, you may
> need to unpick some properties of the client's colour attributes.

My apologies Daniel, I know I'm not following you, but I'll
blunder through a reply anyway, in the hope of stumbling on
some common ground:

I don't think there are any serious issues with rendering for
a single output from multiple source colorspaces within
an application, since the output has a single gamut that can be known.

But given that a surface can span more than one output, there is
no single color space that can simultaneously encompass all outputs
(disparate) gamuts, and yet clip in an application/user preferred
manner. I'm sure that the only way this is doable is for
the application to be able to specify in some non-intent-limited
way a transformation between each source colorspace and each particular
output space. (I say this after many years pondering the ICC's
attempt to decouple source and destination gamuts via the PCS
(Profile Connection Space), even though this is logically impossible.)

> This is quite a big difference from X11, in that there is no longer a
> giant single buffer for all displays. One of the benefits of the
> aggressive decoupling we've done ...

I'm not sure of the relevance. Nothing about application
color management cares about those sort of details. The
primary task is almost always transforming between two
specific device dependent colorspaces. Where the pixels
reside or what the buffers are shared with, or
how the pixels get spatially transformed is mostly irrelevant.
The device colorspaces that the buffers value represent is what's
important from a color management perspective.

Regards,
	Graeme Gill.