: Bogus white point (& colorsync utility)
: Bogus white point (& colorsync utility)
- Subject: : Bogus white point (& colorsync utility)
- From: Chris Murphy <email@hidden>
- Date: Sat, 31 May 2003 16:15:44 -0600
Roger Breton wrote a while back (I'm catching up):
Dear Apple, why would you flag a Media White Point not expressed as
other
than D50 (96.42 100 82.49)? The latest ProfileMakerPro version does
use the
absolute coordinatesfor the white point as the default.
I am at war with anything against the true monitor XYZ in that Media
White
Point tag. Or am I going counter everyone in this war? I got to check
the
lastest ICC specs...
The ICC spec version 4.0 (version 4.0.0 profiles) makes clear that
display profiles should have a white point tag value that is D50
regardless of the actual white point. The 3.0 spec (which gave us 2.0.0
version profiles) was vague on this and those more involved in the ICC
than I care to be have said that the media white point tag was
recommended to be D50. It seems like at the time it wasn't expect that
people would regularly calibrate a display to something other than D50,
so this was rather lose.
The problem with setting the media white point in a display profile to
the actual white point of the display (such as D65), you end up with
double chromatic adaptation. The first adaptation occurs by our visual
system and the second would occur by the CMM. Thus you end up with poor
white simulation (it's too yellow or dark or both).
What I'm a bit sketchy on is why updated CMMs weren't released to
simply ignore the white point tag data in profiles, and just assume a
D50 wtpt tag instead of forcing a change in all display profiles.
Because of the problem of poor paper white simulation and display
profiles reporting the actual white point value in the wtpt tag Adobe
effectively did do this in ACE.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
---------------------------------------------------------
Co-author "Real World Color Management"
Published by PeachPit Press (ISBN 0-201-77340-6)
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