Re: Ooops - D65 != D65 ???
Re: Ooops - D65 != D65 ???
- Subject: Re: Ooops - D65 != D65 ???
- From: Graeme Gill <email@hidden>
- Date: Tue, 19 Jun 2007 11:16:19 +1000
Uli Zappe wrote:
At least part of the mess seems to be that different manufacturers use
the ICC specifications differently (which won't explain the differences
between products of one manufacturer, of course). For instance,
ColorVision obviously writes whitepoint information into the "wtpt" tag
(which seems logical to me); for all X-Rite products, however, "wtpt"
is *always* 0,9642-1,0000-0,8249 on my Mac (maybe the native
whitepoint???), whereas the actual whitepoint settings are stored with
the "lumi" tag, something that the ICC specification explicitly says
should be avoided (ICC.1:2004-10 (Profile version 4.2.0.0), page 32).
Again, it's the "market leader" that looks bad here ...
This is really an ICC problem. There has always been "ambiguity" about
a display profiles white point, since the white point definition is phrased
in terms of a reflective print (is the display white the illuminant color
reflected from the perfect diffuser, or is it the media color when illuminated
with D50 ?) Add in the use of the "Wrong Von Kries" white point transform for
the media white point transform, and there was a problem to be solved.
Unfortunately (IMHO) the ICC has "clarified" this issue with the V4 spec.,
and now mandates that the white points of display be fixed at D50, eliminating
the Absolute colorimetric intent functionality for such profiles, thereby
eliminating the possibility of using such display profiles for side by side
proofing use (at least for any systems that can only access the four standard
ICC intents).
The white point information should be stored in the profile in the
chromaticAdaptationTag instead. Given there is no standard way of
accessing this tag, it's kind of useless to a casual user.
The other interpretation of the V2 spec. is to assume that the
white of a display is the media white illuminated by D50 (just like
high FWA copy paper for instance), and to place it in the white point
tag. You're seeing the difference between these two interpretations.
Graeme Gill.
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