[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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