Graeme Gill schrieb:
Gerhard Fuernkranz wrote:
2. What about Graeme's printer profiles, if the printer was not
characterized for D50, but for a different illuminant? My
understanding is, that Graeme's profiles generally (regardless of the
deivce type) record the absolute color of media white (under the
actual viewing illuminant) in the wtpt tag, and in order to establish
the tables, he transforms the measurements (as measured under the
actual viewing illuminant) with a Bradford CAT from absolute media
white to D50.
I was thinking about that, and with a 'chad' tag I could fix this so
that ICCV4absolute gives a D50 adapted result, while the version
that uses 'chad' will give the selected illuminant result.
I'm not sure what semantics you intend exactly.
However, I agree with Marti, that probably all profiles which do contain
a chad tag should be assumed to follow the V4 semantics, and should be
treated by the CMM like V4 profiles, even if the header indicates V2. I
guess, for most currently existing profiles with chad tag, this is
granted (e.g. the new 2004 sRGB profiles). So if you add a chad tag,
then you should probably build the profile according to the V4 conventions.
Strictly speaking such profiles (those set to use an illuminant other
than
D50) are not ICC compatible,
IMO profiles with an illuminant != D50 *are* indeed ICC compatible
(according to the semantics intended by the ICC), they only have limited
usability.
If no chad tag is present in the profile, then such profiles do not
support the computation of "real" absolute colorimetric intent, but only
the illuminant relative ICC-absolute intent. For the ICC this is not
really a limitation, since they do not define/support a "real" absolute
colorimetric intent anyway.
With chad tag, all intents can be computed by the CMM. And in V4, the
chad tag is also no longer optional, but a mandatory tag, if the
illuminant is != D50.
Regards,
Gerhard
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