[argyllcms] Creating process calibration curves Was: Conversion omitting/locking device colorant

List,

I thought I'd share a little session I had, using xicclu -kv, icclu
and Gnumeric.

Calibration print run on sheet-fed offset press using linear printing plates.
Within tolerances, match as much as possible to standard ISO 12647-2
PT 1&2 (i.e. prim./sec. colors, dot gain)
When dry create device profile from IT8.7/4 chart.

Then:

Target Lab at 25, 50 and 75 K:
icclu -ff -ia -s100 ISOcoated_v2_eci.icc
0 0 0 25
0.000000 0.000000 0.000000 25.000000 [CMYK] -> Lut -> 79.441962
-0.140086 -1.997727 [Lab]
0 0 0 50
0.000000 0.000000 0.000000 50.000000 [CMYK] -> Lut -> 61.806456
-0.147246 -1.553618 [Lab]
0 0 0 75
0.000000 0.000000 0.000000 75.000000 [CMYK] -> Lut -> 41.105493
-0.065598 -0.707456 [Lab]

Target CMY from target Lab:
xicclu -kv -ia -fif ISOcoated_v2_eci.icc
79.441962 -0.140086 -1.997727
79.441962 -0.140086 -1.997727 [Lab] -> Lut -> 0.221580 0.155773
0.166181 0.000000 [CMYK]
61.806456 -0.147246 -1.553618
61.806456 -0.147246 -1.553618 [Lab] -> Lut -> 0.454712 0.353944
0.356616 0.000000 [CMYK]
41.105493 -0.065598 -0.707456
41.105493 -0.065598 -0.707456 [Lab] -> Lut -> 0.720534 0.621456
0.619903 0.000000 [CMYK]

Device CMY needed to meet target Lab:
xicclu -kv -ia -fif Device_Profile.icc
79.441962 -0.140086 -1.997727
79.441962 -0.140086 -1.997727 [Lab] -> Lut -> 0.183225 0.121471
0.145808 0.000000 [CMYK]
61.806456 -0.147246 -1.553618
61.806456 -0.147246 -1.553618 [Lab] -> Lut -> 0.401252 0.306147
0.317546 0.000000 [CMYK]
41.105493 -0.065598 -0.707456
41.105493 -0.065598 -0.707456 [Lab] -> Lut -> 0.660704 0.547960
0.560626 0.000000 [CMYK]

Device K needed to meet L* of target K (iterative user input):
icclu -ff -ia -s100 Device_Profile.icc
0 0 0 21
0.000000 0.000000 0.000000 21.000000 [CMYK] -> Lut -> 79.440394
0.905778 -3.496105 [Lab]
0 0 0 43.5
0.000000 0.000000 0.000000 43.500000 [CMYK] -> Lut -> 61.842308
0.630904 -2.312832 [Lab]
0 0 0 66.8
0.000000 0.000000 0.000000 66.800000 [CMYK] -> Lut -> 41.070386
0.519650 -0.627445 [Lab]

CtP input/output needed:
Cyan    
0       0
22,158  18,3225
45,4712 40,1252
72,0534 66,0704
100     100
        
Magenta 
0       0
15,5773 12,1471
35,3944 30,6147
62,1456 54,796
100     100
        
Yellow
0       0
16,6181 14,5808
35,6616 31,7546
61,9903 56,0626
100     100
        
Black   
0       0
25      21
50      43,5
75      66,8
100     100

Using data above and 3rd deg. poly. regression to calc full range of
smoothed CtP input/output tone values:
%       C       M       Y       K
0       0       0       0       0
5       4,2     4,1     4,5     4,6
10      8,4     8,3     9,0     9,0
15      12,6    12,4    13,4    13,2
20      16,9    16,6    17,8    17,4
25      21,2    20,8    22,1    21,6
30      25,6    25,1    26,5    25,7
35      30,0    29,5    30,9    29,8
40      34,5    33,9    35,4    34,0
45      39,1    38,5    39,9    38,3
50      43,9    43,2    44,6    42,6
55      48,7    48,0    49,3    47,2
60      53,7    52,9    54,2    51,9
65      58,9    58,1    59,2    56,8
70      64,2    63,4    64,4    61,9
75      69,6    68,9    69,7    67,4
80      75,3    74,6    75,3    73,1
85      81,1    80,6    81,1    79,2
90      87,2    86,8    87,1    85,7
95      93,4    93,2    93,4    92,5
100     100     100     100     100

Any thoughts about the process?

Martin Weberg

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