[argyllcms] Accounting for dot gain in press simulation

  • From: Craig Ringer <craig@xxxxxxxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 24 Feb 2011 14:25:30 +0800

Hi all

I've recently been doing some more work using Argyll to produce better profiles of the HP colour laser printer the newspaper I work for uses. I've been using my i1Pro. The goal is to be able to use it for press simulation, so we can soft-proof difficult images instead of just sending them to the press and crossing our fingers. Unfortunately, I'm running into issues that appear to be related to dot gain, and I'm not sure where to go from here.

The very short version: Can ICC profiles account for dot gain? If so, can Argyll help create a profile that does?

The new profiles for the laser printer seem to be pretty good, at least in terms of how well prints correspond to on-display previews in Photoshop in absolute colorimetric proofing mode. Printing and measuring another target, then using that as `profcheck' input, reports DeltaE of 2 on average, peak 5, min 1, so the profile for the laser doesn't seem to be too far out. I'm delighted, as it's *massively* better than the manufacturer-supplied profiles.

The trouble is arising when I try to produce soft proofs of the web offset press using the colour laser printer. Most colours in the proofs are a reasonable match, both with and without paper colour simulation, but certain areas are printing WAY less saturated in the proof than in the final press output. This is most notable in blue skies, where the proof shows a fairly pale blue that's a reasonable match for the on-screen preview, and the press produces a much richer, more saturated blue. I see the same results - and the same issues with those results - when using `tifficc' (lcms) and Photoshop's proof mode. I can't use Argyll's own tiff conversion tool because it doesn't appear to support any device simulation mode.

The press folks say the dramatic colour differences in select areas is a dot gain issue caused by the inks bleeding out into the paper. That's an issue I'm familiar with, but haven't seen having this dramatic an effect before. This leads me to my main question: Can an ICC profile reasonably account for the 30% dot gain of an offset web litho press, and if so are there any facilities in Argyll CMS to create a profile that tries to handle dot gain? Am I likely to be correct in suspecting that their current profile just isn't a particularly accurate match for their actual press output?

I'm thinking of doing a minimum print run of swatches on the press, creating them using targen and using the old press profile as a guide for swatch selection. Measuring that and feeding it to `profcheck' shoudl give me a reasonable estimation of the accuracy of the current profile (right?) and allow me to produce a new profile that might be better if I've printed enough swatches. The press probably has a rather non-uniform colour space, so I'd love some guidance about how many swatches would be reasonable for getting a decent profile if I did want to try to create a new one.

Just to complicate things a little more, the paper stock is off-white (creamy), though at least it's without any FWA. The existing profile was produced using that stock, so at least we're not lying to the CMS and pretending to be printing on white stock.

Craig Ringer

Tech-related writing at http://soapyfrogs.blogspot.com/

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