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

[Graeme Gill]

Pekka Paalanen wrote:

Hi,

> I'm still wondering, if an application uses an ICC profile for the
> content it provides and defines an intent with it, should a compositor
> apply that intent when converting from application color space to the
> blending color space in the compositor?

yes it should, since this is a standard expectation of applications
that make use of ICC profiles to do color management, and is
standardly supported by the CMM's used to perform such conversions.

> Should the same application provided intent be used when converting the
> composition result of the window to the output color space?

No, this wouldn't make sense. The applications intent in converting
from the source space to the displays space has been executed and
is then represented in the output space pixel values.

In any case, I don't think the compositor should be changing
colorspaces for the purposes of compositing buffers together
for an output. All the source elements to be composed should
be in the output colorspace before composition. The only
modifications I can imagine would be for the purposes of linear
light blending, and this should aim to have no impact
on the color fidelity.

> Do I understand correctly that an ICC profile can provide separate
> (A2B and B2A) cLUT for each intent?

Yes, that is how it is implemented in cLUT based profiles. There is
no normally no table for Absolute Colorimetric - the Relative
Colorimetric table is used with an adjustment based
on the white point tag. (Exception is for the ICC V4
floating point cLUTs - it's possible to have an explicit
Absolute Colorimetric table in that case.)

> Btw. wl_surface.enter/leave is not unambigous, because they may
> indicate multiple outputs simultaneously. I did talk with you about
> adding an event to define the one output the app should be optimizing
> for, but so far neither protocol proposal has that.

Right, neither proposed protocol seems to make allowances
for some of the suggestions discussed.

I'm maintaining a summary of my current thinking here:
<http://www.argyllcms.com/WaylandCM_v1.txt> for anyone interested.

Cheers,
	Graeme Gill.