[argyllcms] Re: Accounting for dot gain in press simulation
- From: Craig Ringer <craig@xxxxxxxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 02 Mar 2011 13:28:16 +0800
On 24/02/11 17:49, Graeme Gill wrote:
> Right, but you can do that with Argyll too, if you trust such a process.
> Simply string your RIP simulation transform ahead of the proofing
> transform using cctiff.
I'll give that a go and see how it compares to Photoshop and lcms's output.
> You are assuming a lot about the color transformations being done
> in the RIP though, which is why I've never seen the point of such
> emulation modes.
Colour trans-what?
The press folks have pretty much lobotomized their RIP. It's been told
to ignore all ICC colour tagging. They require us to send untagged
CMYK-only PDF to them with all colours pre-converted into the colour
space of their supplied profiles.
That's not to say that it isn't applying some kind of generic
transformation curves, or configured to assume input data is in profile
<x> and transform to profile <y>. They're not good at communicating
about these things, and I can't help feeling like they think their RIP
is black magic. Since they recently upgraded to new presses without a
big change in printed results, I suspect they must be doing *some* kind
of transform in the RIP. So long as it's consistent from run to run and
reasonably uniform, though, I can account for it in the profile as part
of the "device" characterization. I don't really have to care whether a
given colour shift is caused by the RIP or the press its self. At least,
such is my understanding.
I'd eventually like to get their RIP doing identity transforms (hands
off my colour!) simply because it'll give me a wider gamut to play with,
but for now I just want to be able to predict what'll print.
> Much better not emulating it, instead use the real
> thing. You are in trouble with originals that have complicated
> color treatment too (ie. different colorspace source objects in them,
> which is not atypical of PS and PDF.)
The printing company rejects mixed-space or ICC profile tagged PDF. We
have to send plain old untagged CMYK. So I guess that won't be much of
an issue.
I avoid mixed-space PDF like the plague anyway. It's too vulnerable to
the innumerable different bugs in PDF processors and colour management
engines.
>> Agreed - if you do devote a press run to profiling (which we've done
>> before) it's worth putting some photos on the sheet along with the
>> patches - just so the press operator has something on the sheet that
>> looks like a "real" job. It also gives you something to evaluate your
>> proofs against, because you'll notice colour errors in a photo with
>> skin-tones way sooner than you will a random field of coloured patches.
>
> The real benefits of profiling the press depend on the press being
> set to the same operating state all the time, and not adjusting it
> for each job that comes through. This often seems foreign to old
> time press operators.
Yep, it certainly is to these guys. I'm working on that with them at the
moment, but they're very old-school and I don't know how far I'll get.
--
Craig Ringer
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