(taking Richard out of CC as he replied on list)
Am 19.06.2013 04:52, schrieb John Kåre Alsaker:
Here is my current color management protocol for Wayland clients. The
basic idea is that the compositor sends two color spaces to the
clients. A compositing color space which the compositor prefers since
it would require no conversions. A full-screen color space which the
compositor can be able to scan out from. The full-screen color space
is intended to used by games which are able to do color conversions as
part of their post-processing. It's also possible it could be used by
video players.
Just rewording to get all in sync about the terms.
The "compositor colour space" appears like a kind of document colour
space, which the desktop/display is in. In the existing colour managed
compositors that defaults to sRGB, but can of course be a different
space like you suggest here.
The "full-screen color space" reads like the main outputs device space.
Is that notation correct?
For various clients it would be essential to see each outputs native
space as well. Multi monitor aware colour correction in some essential
for artists applications as well as analysing software come to mind.
Different rendering intents and more advanced color spaces have not
explicitly been considered here, but I hope the use of ICC profiles
will cover these.
From a architecture point of view, that is not so easy. There are few
CMS'es around to modify the rendering bits in a ICC profile. Secondly as
the profiles are passed by file name, that would require copying before
giving to Wayland, which sounds unfortunate and might cause confusion
later on.
Calibration tools will require explicit privileges in order to do
their job. Using the full-screen color space won't be enough since
video card gamma correction can apply to it. I also wonder if we can
just remove the VCGT tag from the ICC profiles to indicate that the
client doesn't have to correct for that, but I'm not sure that anyone
would use the tag anyway.
Sending a faked "no VCGT" profile is slightly indirect, but might work
out. That needs to be documented very well. A calibration/profiling
program needs then to set the VCGT-less profile to the output in
question and then displays its measurement patches on a surface without
colour conversion.
To deprecate the VCGT tag is not so easy, as we have lots of legacy
profiles around from windows / osx software and directly from vendors.
Ignoring the VCGT tag is no option, modifying the profile by baking the
VCGT tag into the ICC standard colorimetric descriptions might be a
workaround inside a CMS.
kind regards
Kai-Uwe
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