[argyllcms] Re: Gamut mapping problems in 1.1.0

  • From: Idea Digital Imaging <qcore@xxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 10 Nov 2009 12:31:41 +0000

On 10 Nov 2009, at 01:07, Graeme Gill wrote:

Idea Digital Imaging wrote:

The only real concern was that we were losing saturation in delicate skin tones -- just like the glow in the petals that I mentioned above.

OK, that sounds a bit more like the saturation well within the gamut,
so perhaps I should bump the "knee" value up a bit more to address
this (that's the gamknf value in the xicc/xicc.c file for those
who compiled from source who would like to play with it).

Sorry Graeme I should have used some real images and a viewing booth but had access to neither on Friday night when I was tinkering -- I'm going to delete those test images from my laptop immediately!

So back to the viewing booth, the images that were evaluated yesterday were originally Adobe RGB going to ISO Coated v2 (300) and our own in-house images are normally DonRGB.

We use tiffgamut -pj -cmt and then feed the gam data into collink using collink -ip -ke -cmt -dpp -G.

First question: in tiffgamut would there be any benefit to us using - ip or -is?

I'll have a go at playing with the knee value to see what difference it makes to the saturation in the skin tones.

Next question: if we still feel that we'd like *slightly* more saturated results overall from our workflow and would just like to tweak this a little -- what would be the best way to do this? Can we achieve it simply by changing the tiffgamut/collink intents or viewing conditions, or do we need to adjust and recompile collink?

Actually, when I say "more saturated" I think that this term might be confusing. What I mean is that I've got nothing against clipping in the resulting CMYK or a lack of smoothness _providing_ it works to the benefit of the image in print.

Which leads on to a related question, a question that is probably for Klaus. The 1.1.0 Beta version of collink in GaMapICC0.3b does some interesting things to saturated colours making them look as if they've been through wide radius/small value unsharp masking.

Although this was generally agreed to be "a bit too much" in yesterday's test images -- chunky blue wool fabrics lost their softness and green garments became a bit glossy -- being able to boost the contrast in saturated colours *slightly* is of great interest because it saves us from having to apply USM afterwards as we routinely do ourselves.

If it isn't a secret sauce recipe, can you let me know I can adjust collink to achieve a little of the this effect?


Martin Orpen
Idea Digital Imaging Ltd

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