Graeme Gill wrote:
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]
Graeme, yes, looks much more reasonable now :-)
xicc/xicclu -ip -fb -pl CHP410-1200.icmSorry for my ignorance - aren't you using the the line segment between bkpt..wtpt (in CIECAM space, thus it is a slightly bent curve in CIELAB) as perceptual black axis? And doesn't perceptual intent map the PCS gray axis Lab=[0,0,0]..[100,0,0] to the perceptual gray axis? If so, why doesn't PCS [0,0,0] map to the bkpt?
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.)
I've already seen in the code, and I actually find this a good idea.
Best Regards, Gerhard
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.
