[argyllcms] Re: Collink and device link profiles

  • From: Michael Schulz <ms.typografik@xxxxxx>
  • To: <argyllcms@xxxxxxxxxxxxx>
  • Date: Fri, 08 Jul 2011 10:26:35 +0200


thank you for the reply and for the indication how to check the result with
cctiff. In the meantime I did more trials with collink's device link option.
What I found out is, there is a slight yellow colour cast in the converted
images (rgb2cmyk and cmyk2cmyk) - I misunderstood this as an over
saturation. It becomes visible in skin tones and noticeably if one compares
the yellow colour channels of images that have been converted across the PCS
with device link conversions.

I don't understand where it comes from but I assume that it might be the
black ink generation and not the gamut mapping. I tried -ke, -kt, -kx, -kr
and -kh; beside of the yellow colour cast -kt gives the best results. Does
it makes any sense trying a black ink generation with the -kp... flag?

What I don't understand in your answer is the last paragraph - why do one
gets multiple gamut mapping transformations? I thought with device link
profiles there is only one B2A table used?

If you want to look at my test images:


Best regards
Michael Schulz

Am 28.06.2011 1:44 Uhr schrieb "Graeme Gill" unter <graeme@xxxxxxxxxxxxx>:

> Michael Schulz wrote:
>> the device link profiles (cmyk2cmyk) are not giving exactly
>> similar results, but they all have in common an over saturation -
>> particularly visible in pixel images, not so in pure colour surfaces (cm,
>> cy, my, c, m, y).
>> Here again the command lines I used:
>> -v -qh -G -ke -fk -cpp -dpp inprofile.icc outprofile.icc DL_in-out.icc
> I'm unable to see such an effect for this set of options. If I check the
> result
> using a cmyk test image like this:
> cctiff -t1 -ir ISOcoated_v2_eci.icc cmyk_testiamge.tif ISOcoat.tif
> cctiff -t1 ISOcoat_2_ISOuncoat.icc -ir ISOuncoated.icc testiamge.tif
> ISOuncoat.tif
> I get an output that is noticeably less saturated, as expected due to the
> smaller gamut of the destination profile.
> [ I'm not sure what you are trying to achieve using -ke and -fk. This may
> give a rather bumpy result due to a crossover between the different black
> values near neutral. A better combination is probably -kt -fk. ]
>> -v -qh -G -ke -fk -fcmy -cpp -dpp inprofile.icc outprofile.icc DL_in-out.icc
>> the same also with -kt, -is and -ims
> Naturally you may get more saturated results using -is and -ims,
> since these are saturation intents.
> It's possible that -fcmy may give some similar effect, if the
> destination primaries were more saturated than the source, since you
> would be forcing a smooth mapping between them.
>> I don't understand what is causing this over saturation with cmyk2cmyk
>> device link profiles, because rgb2cmyk device link profiles gives much
>> better results.
> Are you sure that it's real ? If you preview the output using (for example)
> the perceptual B2A table of the colorspaces (which is the default rendering
> intent of the profiles you are using), you will get multiple gamut
> mapping transformations due to the concatenation of the devices link
> with whatever gamut mapping is in the device profile perceptual B2A table.
> Graeme Gill.

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