[argyllcms] Re: xicclu -g predictability issue

  • From: Elena [service address] <1007140@xxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 28 Jan 2011 23:21:16 +0100

Hello Gerhard

No, the problem is more severe and it has been understood, it's due to
discontinue CMYK combinations (well, actually clusters of them) in the
3d x 4d b2a grid which are colorimetrically correct but nonetheless discontinue,
so interpolating points at their boundaries causes colorimetrical errors.

Reducing the problem to the bones, i.e using a perceptual devicelink profile 
(thus
avoiding additional PCS conversions and relative interpolation artifacts)
and analyzing this way the RGBxCMYK grid (which is easier, and contains no 
clipped
colors) is the best way to understand and detect such problems.

Firstly, if you will like to further play/test with my data, I strongly
suggest you to use a more precise and recent .ti3 (an ofps3000 reading
averaged + some additional patches):
http://www.elenadomain.it/pub/argyll/ofps3000+ab.ti3
(Well, not really averaged because of Average bugs. It's two readings
merged in one .ti3 to be averaged by colprof).

And one such device link profile computed on a profile based on the data
above, with -G -ip -r100 -k[same of the linked profile, 0 0 1 .2 .5]
http://www.elenadomain.it/pub/argyll/link-srgb-test5_r100.icm [~8 MB]

Then, have a look at the attached plots of slices from the relative rgb x cmyk 
table.
Those are just a couple of troublesome areas (slices intersecting the bumps).
Note the disaster in RtoK. Note the mess in GtoK. Those ink swappings aren't
good at all. See also the WtoK for reference (as predicted by xicclu). I 
understand
that following that selected curve could lead to less gamut in (for example) 
dark
reds or dark greens, but those cmyk combos with K ramping up shouldn't be 
allowed
at all. So I really wonder which sense does it have at all to be able to set a K
separation curve if for colored tints this curve is not respected at all...

/&


> Using a profile created from Elena's ofps2.ti3 data I did take a closer
> look at a short line crossing one of the discontinuities (a straight
> line in the source sRGB space, which is then converted with perceptual
> intent to CMYK).
>
> And it seems to happen at a location where CMYK colorants are crossing
> very steeply. Note that the 101 CMYK points below spawn only a couple of
> dE in total!
>
> So possibly limiting the 1st derivatives may be a key to success?
>
> Regards,
> Gerhard
>
>
> CMYK:
>
> 147.589056 255.000000 211.444246 89.639688 
> 147.449397 255.000000 210.761833 89.712065 
> 147.308818 255.000000 210.074727 89.782636 
> 147.170518 255.000000 209.391281 89.855917 
> 147.034468 255.000000 208.700696 89.937364 
> 146.901143 255.000000 208.023385 90.017281 
> 146.765950 255.000000 207.336725 90.093578 
> 146.627302 255.000000 206.645558 90.169091 
> 146.489000 255.000000 205.962169 90.242415 
> 146.353461 255.000000 205.280502 90.320620 
> 146.215817 255.000000 204.597959 90.396720 
> 146.081621 255.000000 203.968098 90.452620 
> 145.949232 255.000000 203.354775 90.501377 
> 145.810954 255.000000 202.670778 90.574248 
> 145.672124 255.000000 201.972192 90.651061 
> 145.531704 255.000000 201.290138 90.721289 
> 145.391961 255.000000 200.610167 90.794034 
> 144.182603 255.000000 199.057745 93.181536 
> 142.836807 255.000000 197.390225 95.886130 
> 141.479385 255.000000 195.713618 98.610302 
> 140.123599 255.000000 194.036280 101.328329
> 138.768033 255.000000 192.360995 104.041099
> 137.419200 255.000000 190.699474 106.738508
> 135.991107 255.000000 189.001333 109.540815
> 133.657102 255.000000 186.854668 113.670524
> 131.345426 255.000000 184.735313 117.744530
> 129.055728 255.000000 182.633536 121.791799
> 126.781979 255.000000 180.531665 125.823717
> 124.525324 255.000000 178.442086 129.829509
> 122.211695 255.000000 176.320001 133.908049
> 119.917316 255.000000 174.210671 137.963117
> 117.609610 255.000000 172.087952 142.042274
> 115.306966 255.000000 169.975948 146.109491
> 113.026311 255.000000 167.872001 150.145138
> 110.838269 255.000000 165.896934 153.972360
> 108.629399 255.000000 163.923790 157.808097
> 106.319631 255.000000 161.810632 161.882351
> 103.999040 255.000000 159.688147 165.968016
> 101.689057 255.000000 157.569032 170.045755
> 99.382821 255.000000 155.461212 174.107905 
> 97.126022 255.000000 153.371874 178.116895 
> 94.910014 255.000000 151.320790 182.046916 
> 93.548516 255.000000 149.655968 184.747269 
> 92.316971 255.000000 148.170133 187.160532 
> 91.677646 255.000000 147.076950 188.593787 
> 92.242144 255.000000 146.631504 188.169886 
> 92.716109 255.000000 146.242452 187.783530 
> 93.298697 255.000000 145.777325 187.347602 
> 93.778586 255.000000 145.384752 186.955806 
> 94.367943 255.000000 144.911438 186.518649 
> 94.952626 255.000000 144.444399 186.079403 
> 95.539136 255.000000 143.975065 185.636496 
> 96.119132 255.000000 143.549055 185.107810 
> 96.655231 255.000000 143.263182 184.267993 
> 97.193897 255.000000 142.973358 183.431315 
> 97.732562 255.000000 142.683533 182.586854 
> 98.320924 255.000000 142.365907 181.698598 
> 98.922702 255.000000 142.045640 180.797356 
> 99.459961 255.000000 141.757177 179.959140 
> 100.054316 255.000000 141.439588 179.063712
> 100.709509 255.000000 141.091611 178.115308
> 101.293238 255.000000 140.780182 177.230329
> 101.911235 255.000000 140.453769 176.316943
> 102.564583 255.000000 140.107411 175.368235
> 103.214919 255.000000 139.761912 174.413771
> 103.894318 255.000000 139.477953 173.398066
> 104.620464 255.000000 139.249432 172.318824
> 105.341088 255.000000 139.021750 171.244494
> 106.077424 255.000000 138.792396 170.157694
> 106.911463 255.000000 138.545068 168.961785
> 107.660458 255.000000 138.315507 167.870494
> 108.507466 255.000000 138.064328 166.663841
> 109.248458 255.000000 137.833337 165.571516
> 110.106763 255.000000 137.580914 164.356675
> 110.973400 255.000000 137.327208 163.129303
> 111.822266 255.000000 137.076218 161.916984
> 112.681465 255.000000 136.819130 160.696892
> 113.459545 255.000000 136.462129 159.515640
> 114.217251 255.000000 136.063525 158.328681
> 114.876571 255.000000 135.692870 157.252430
> 115.136869 255.000000 135.432072 156.603978
> 115.426243 255.000000 135.153801 155.918372
> 115.721726 255.000000 134.870501 155.221065
> 116.011637 255.000000 134.588929 154.528382
> 116.335387 255.000000 134.294104 153.800065
> 116.625809 255.000000 134.013744 153.117463
> 116.929221 255.000000 133.728261 152.411349
> 117.252326 255.000000 133.433799 151.682330
> 117.577618 255.000000 133.139903 150.957309
> 117.908354 255.000000 132.844907 150.224762
> 118.244034 255.000000 132.549426 149.494801
> 118.626113 255.000000 132.230007 148.697238
> 118.951057 255.000000 131.936211 147.968618
> 119.261596 255.000000 131.647459 147.255021
> 119.625807 255.000000 131.352506 146.456192
> 120.002946 255.000000 131.072871 145.649662
> 120.401646 255.000000 130.807412 144.843558
> 120.843805 255.000000 130.523299 143.989684
> 121.280416 255.000000 130.238598 143.137523
> 121.706807 255.000000 129.957912 142.289783
> 122.130124 255.000000 129.678641 141.449747
>
>
> CIELAB numbers resulting from softproof:
>
> 35.536612 10.253407 8.588838                                              
> 35.531993 10.289458 8.522461                                              
> 35.525190 10.326883 8.456049                                              
> 35.518293 10.363600 8.389875                                              
> 35.511013 10.399475 8.322734                                              
> 35.503784 10.434761 8.256445                                              
> 35.496596 10.470825 8.189692                                              
> 35.489532 10.507643 8.122524                                              
> 35.482636 10.544354 8.055323                                              
> 35.475551 10.580153 7.988108                                              
> 35.468584 10.616517 7.920860                                              
> 35.462709 10.652525 7.859384                                              
> 35.457225 10.688257 7.800620                                              
> 35.450320 10.725022 7.734385                                              
> 35.443096 10.761987 7.666564                                              
> 35.436393 10.799260 7.600700                                              
> 35.429662 10.836143 7.535014                                              
> 35.440762 10.868077 7.441352                                              
> 35.462915 10.913448 7.344791                                              
> 35.567485 11.102700 7.250909                                              
> 35.685287 11.279161 7.214756                                              
> 35.812241 11.450015 7.207985                                              
> 35.951771 11.580591 7.177563                                              
> 36.121906 11.619116 7.095966                                              
> 36.373795 11.690774 7.027561                                              
> 36.624217 11.762486 6.960854                                              
> 36.811292 11.819631 6.947351                                              
> 36.935711 11.891293 7.008322                                              
> 37.043508 12.002570 6.985327                                              
> 37.178690 12.168376 6.942854                                              
> 37.312205 12.333985 6.899755                                              
> 37.393132 12.496392 6.875480                                              
> 37.343933 12.650321 6.896518                                              
> 37.211179 12.659072 6.832382                                              
> 37.070685 12.641777 6.757998                                              
> 36.929313 12.625570 6.684488                                              
> 36.896335 12.665721 6.615757                                              
> 36.731782 12.735819 6.597360                                              
> 36.580841 12.665540 6.516897                                              
> 36.417064 12.540413 6.415430                                              
> 36.255344 12.415878 6.314391                                              
> 36.113015 12.320144 6.230710                                              
> 35.987979 12.256859 6.220574                                              
> 35.864440 12.194201 6.229447                                              
> 35.788496 12.101897 6.198255                                              
> 35.776484 12.128652 6.147188                                              
> 35.769927 12.134006 6.095506                                              
> 35.761916 12.122220 6.028268                                              
> 35.756772 12.116082 5.971776                                              
> 35.748399 12.103863 5.903639                                              
> 35.740444 12.092237 5.836116                                              
> 35.732436 12.080373 5.768086                                              
> 35.740607 12.095923 5.712688                                              
> 35.770852 12.146033 5.664809                                              
> 35.801008 12.196696 5.616588                                              
> 35.831364 12.247758 5.568306                                              
> 35.862725 12.300055 5.516033                                              
> 35.894543 12.352675 5.462972                                              
> 35.924784 12.403005 5.414736                                              
> 35.956451 12.454747 5.362167                                              
> 35.989409 12.507817 5.304951                                              
> 36.020810 12.559183 5.253266                                              
> 36.052919 12.611097 5.199122                                              
> 36.086155 12.664696 5.142001                                              
> 36.119511 12.718707 5.084916                                              
> 36.157214 12.774783 5.029673                                              
> 36.198742 12.832352 4.975781                                              
> 36.240118 12.890233 4.922130                                              
> 36.275773 12.943794 4.876221
> 36.280472 12.943952 4.812306
> 36.263691 12.935970 4.747105
> 36.244791 12.925413 4.674562
> 36.228732 12.918728 4.609805
> 36.209414 12.907359 4.536567
> 36.190064 12.896126 4.462672
> 36.170996 12.885165 4.389839
> 36.151329 12.874181 4.316113
> 36.131087 12.873434 4.238046
> 36.134110 12.913385 4.157002
> 36.140707 12.957436 4.083282
> 36.149819 13.000494 4.041645
> 36.158644 13.044242 3.996662
> 36.167790 13.089013 3.951128
> 36.176822 13.133703 3.906075
> 36.185453 13.178556 3.858175
> 36.194014 13.222170 3.813995
> 36.202887 13.266802 3.768537
> 36.211683 13.311965 3.721150
> 36.220212 13.356491 3.673748
> 36.228706 13.400988 3.625943
> 36.238801 13.425859 3.568431
> 36.250805 13.436175 3.497613
> 36.262762 13.449061 3.434240
> 36.275125 13.463060 3.372467
> 36.288755 13.474771 3.304247
> 36.303025 13.484968 3.236860
> 36.316829 13.491665 3.169371
> 36.330461 13.496067 3.096409
> 36.344431 13.501415 3.023685
> 36.358577 13.507511 2.952143
> 36.372518 13.513477 2.881106
>
Regards

Attachment: GtoK.png
Description: PNG image

Attachment: RtoK.png
Description: PNG image

Attachment: WtoK.png
Description: PNG image

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