[argyllcms] Re: perceptual black too light
- From: Graeme Gill <graeme@xxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Sun, 12 Feb 2006 15:02:54 +1100
Gerhard,
using a more robust search for the black point (20 trials with
random starting points) on your data set results in the following:
XYZArray:
No. elements = 1
0: 0.018478, 0.018829, 0.015137 [Lab 14.860508, 0.784551, 0.455625]
xicc/xicclu -ip -fb -pl CHP410-1200.icm
0.000000 0.000000 0.000000 [Lab] -> Lut -> 0.999641 0.101813 0.132937 1.000000
[CMYK]
Note that Lab 0 0 0 returns the closest point from the perceptual table,
not the black point. Profile chooses the black point to be the lowest
L point within the gamut with the same direction as K only. (This
seemed a reasonable thing to me, since K only is often used as a reference
black hue within CMYK systems.) There may be points in the gamut with a
lower L, but they may have a not so neutral color.
xicclu -ia -ff -pl CHP410-1200.icm
0.999641 0.101813 0.132937 1.000000 [CMYK] -> Lut -> 13.500272 0.608876
-3.316293 [Lab]
/src/argyll/test/gfuer2:../../xicc/xicclu -ia -fif -pl -l250 -kh CHP410-1200.icm
15.000000 0.800000 0.400000 [Lab] -> Lut -> 0.222745 0.177431 0.194287 0.998518 [CMYK] Lim 1.592982
14.000000 0.800000 0.400000 [Lab] -> Lut -> 0.292572 0.228957 0.231581 1.000000 [CMYK] Lim 1.753109
(clip)
13.000000 0.800000 0.400000 [Lab] -> Lut -> 0.292572 0.229783 0.141170 1.000000 [CMYK] Lim 1.663525
(clip)
Which is consistent with what profile found. Does this seem a better result ?
[Thanks for drawing this problem to my attention.]
Graeme Gill.
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