Gerhard Fuernkranz wrote:
And with absolute intent, the CMYK numbers of "perceptual black" map very close to the 'bkpt' of the profile.
Graeme,
FYI, below is an example for the mentioned problem.
The example is CMYK. I also tried a RGB profile - and here I did not see the problem (B2A0 maps black to RGB=0)
Regards, Gerhard
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# create CMYK profile $ profile -v -qm -r1 -c3 -d0 -l250 -kh -S sRGB.icm CHP410-1200 [...]
iccdump sais:
tag 3:
sig 'bkpt'
type 'XYZ '
offset 436
size 20
XYZArray:
No. elements = 1
0: 0.044571, 0.045456, 0.039139 [Lab 25.398841, 1.001780, -1.027158]
$ xicclu -ip -fb -pl CHP410-1200.icc
0 0 0
0.000000 0.000000 0.000000 [Lab] -> Lut -> 0.469035 0.402268 0.352447 0.780039 [CMYK]
$ xicclu -ir -ff -pl CHP410-1200.icc
0.469035 0.402268 0.352447 0.780039
0.469035 0.402268 0.352447 0.780039 [CMYK] -> Lut -> 28.543165 0.190091 2.979273 [Lab]
==> B2A0 maps PCS black to to L* 28.5 !!!
-Gerhard
$ xicclu -ir -fif -pl -l250 -kh CHP410-1200.icc
30 0 0
30.000000 0.000000 0.000000 [Lab] -> Lut -> 0.659153 0.569678 0.464360 0.648054 [CMYK] Lim 2.341245
25
25.000000 0.000000 0.000000 [Lab] -> Lut -> 0.633084 0.518622 0.358723 0.804912 [CMYK] Lim 2.315342
20
20.000000 0.000000 0.000000 [Lab] -> Lut -> 0.677642 0.523342 0.252456 0.933065 [CMYK] Lim 2.386506
18
18.000000 0.000000 0.000000 [Lab] -> Lut -> 0.874339 0.463151 0.211874 0.971778 [CMYK] Lim 2.521141
17
17.000000 0.000000 0.000000 [Lab] -> Lut -> 0.850269 0.379570 0.135089 0.990474 [CMYK] Lim 2.355402
16
16.000000 0.000000 0.000000 [Lab] -> Lut -> 0.987146 0.209901 0.141170 1.000000 [CMYK] Lim 2.338217 (clip)
==> But as you can see, even Lab [17,0,0] is reproducible on the device, only [16,0,0] is slightly clipped.
For comparison, RGB:
$ xicclu -ip -fb RGBprinter.icc
0 0 0
0.000000 0.000000 0.000000 [Lab] -> Lut -> 0.000000 0.000000 0.000000 [RGB]