[argyllcms] Re: Gamut mapping problems in 1.1.0

  • From: Klaus Karcher <lists@xxxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 12 Nov 2009 20:22:57 +0100

Idea Digital Imaging wrote:
The debate of re-target/re-purpose is interesting though. In my case I operate in the "ambiguous" category. The original images have been extensively retouched in an RGB working space and nobody would want to refer back to the original scene :)

This means that the separation for proof/print can be a mixture of re-purposing/re-targeting.

I know what you mean as I'm in similar situations frequently.

A good example might be the development of a key visual for a brand or an advertising campaign.

If the job is running well, we get RGB TIFs together with RAW files from the photographer. The RGB TIFs are the photographer's interpretation of how the image should look on an ideal medium and they are normally already cleared with the customer on screen (usually already in the photo studio during or subsequent to the shooting). The RAW files are kind of backup or safeness if something went wrong in the initial processing or if the customer has second thoughts. But already the "original" RGB TIF is ambiguous: we can never be sure to see what the photographer and the client saw (as long as we are not sit in on the shooting/clearance). What they saw is the image in the RGB working space clipped to the display gamut. It strongly depends on

- the gamut of the photographer's monitor
- the viewing conditions in the studio (often very dark)
- the state of adaptation of the viewers
- the quality of the display profile

So the question is always: did they see what we see? Is e.g. the oversaturated red we see intentionally or did they see a clipped version? Is the clipping /we/ see intentionally? Did they desaturate the greens intentionally or enforced by the gamut limits of the equipment (I don't want to consider the Photoshop skills of the photographer as another possible limiting factor for the moment ;-)

The next input are the creative ideas of the advertising agency involved. Our struggle consists in brining together the parts and ideas an to merge them to something thats actually printable -- often for a variety of different media like sheetfed and web offset, various flavors of gravure printing, digital large-format printing on all kinds of substrates and -- far the worst -- Newspaper.

The first tuning phase takes place by means of proofs for /one/ printing condition -- almost always FOGRA39 / ISO coated v2. The Photoshop file always stays in the RGB working space and the operator has to switch between the normal display, ISO coated v2 softproofs and softproofs for other important printing conditions.

At the latest when the point is to adapt the approved ISO Coated v2 proof to other printing conditions, the pipe dream of a "media independent" ICC workflow goes up in a cloud of smoke. Normally we end up with an master RGB Photoshop file with a bunch of layer sets on top of the virtual composing -- one set for each printing condition. It's not that the main purpose of these correction sets is to compensate for the different gamuts of the printing processes, but for the flaws and quirkinesses of the respective output profiles and the variations between vendor depended gamut mapping strategies. We have to stick with these output profiles as they are branch standards and the recipients expect (rightly) PDF/X files with the respective profile embedded as well as separations that correspond to the embedded profile.

A consistent, decent gamut mapping combined with the chance to "copy" the separation behavior of a given profile is the key to improve this unfortunate situation substantially IMHO. And Argyll is on a very good way to provide both.

So: congratulations, Graeme -- the upcoming release will be a great leap forward once again :-)


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