Re: Microsoft's color-management claims
Re: Microsoft's color-management claims
- Subject: Re: Microsoft's color-management claims
- From: Graeme Gill <email@hidden>
- Date: Thu, 22 Sep 2005 22:01:08 +1000
Roger Breton wrote:
The WCS device independent space is just
the measured device CIE values (as I read their doco..).
But, Graeme, by "device CIE values" can only mean that the tristimulus
integration has already taken place. How can their "profiles" use a "device
independent colorspace" that is also "illuminant independent" if they use
CIE values: will they achieve the viewing conditions through chromatic
adaption like the rest of the color folks do it? I mean, in order to do the
things WCS promises, don't they need more than the "device CIE values" but
more importantly the spectral data?
Maybe, maybe not. It's not entirely clear from the current WCS documentation.
There is reference to XYZ values, so presumably white point shifts will
be using chromatic adaptation (which is what CIECAM02 will do).
The term "illuminant independent" could just mean that the CIE
values are not tied to a particular illuminant such as D50.
What about in argyll, at link-time, do you simply use the "device CIE
values" or do you also need the "device spectral values"?
Since I'm fitting in with ICC profiles (which have no capability
to represent spectral profiles), conversion from spectral to CIE
values happens at profiling time. For strict ICC conformance, the
illuminant will be D50. It is possible to make non-ICC conforming
profiles by specifying an alternate illuminant, but it's up
to you then, to make sure you know what you're doing. If
your intended viewing conditions are not D50, then it would
make sense to do this, but it's not possible to do this at
link time.
It would be technically easy to expand the ICC format to include
a colorimetric spectral forward profile (Argyll in fact has a
model based profile format that supports spectral information,
but it's used for another purpose), and this would allow the
illuminant to be specified at link time with negligible
extra overhead. (That's one of the things on my list of
changes that should be being made to the ICC format!)
Graeme Gill.
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