[argyllcms] Re: Measuring a colorcheker on screen
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 25 Jan 2008 16:29:53 +1100
Kai-Uwe Behrmann wrote:
ICC(v4.2) D 7.2 clears about display handling as a emmisive device:
"Thus, for practical reasons, it is important that the monitor profiles be
designed to display paper white at full-drive monitor white (R = G = B =
255 on a typical 24-bit display). Similarly, there is an expectation that
R = G = B = 0 corresponds to "black" and will be reproduced by the minimum
reflectance of the output medium. These user expectations are based on
common practice and convenience and lie outside of strict colorimetry and
colour-appearance considerations."
Right, but the intent used to link the input to the display profile
will have an effect as well. If you link an idealized RGB input profile
(say sRGB) with an actual display profile with a non-zero black point
using relative colorimetric intent (or a good perceptual intent etc.),
then asking for XYZ = 0,0,0 is outside the gamut of the display
device, and it will clip to its minimum possible black, satisfying the
above requirements. ie., the above guidance does not imply that
a display profile must have a black point of 0.
The ICC rendering intent selecton should play no role for display
profiles.
It should, if either the CMM provides such mechanisms (as for instance
icclink -g does), or if the display profile contains different tables
for each intent (as ICC V4 allows for - see V4.2 pp 28, table 21).
Graeme Gill.
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