[argyllcms] Re: perceptual black too light
- From: Gerhard Fuernkranz <nospam456@xxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 10 Feb 2006 22:23:28 +0100
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
--------------------------------------
# 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 !!!
$ 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]
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