Re: GRACoL densities
Re: GRACoL densities
- Subject: Re: GRACoL densities
- From: Roger Breton <email@hidden>
- Date: Mon, 02 May 2005 08:45:12 -0400
Terry,
You and Ray got me convinced: it's a function of paper and press condition
and instrumentation. And there ought to be some indication of that fact in
the GRACoL book!!
> I concur with Ray. I did a press profiling job a few months ago where I
> had access to an X-Rite ATS scanning spectro unit. We did the run to
> GRACoL SIDs and I scanned/measured the color bars wet and then every
> couple of hours for 24 hours after that. With THAT ink set we saw cyan
> drop about .07 and the magenta only about .03. Black dropped nearly
> .15. We then changed ink sets and ran the test again (same stock). THIS
> time the CMY only dropped about .03 and the black about .07-.10. So it
> varies depending on ink at least.
> Beware of the instrument you're using also! I've run into several shops
> lately using polarized densitometers (typically Gretag D19C w/ Status
> T/P filters).
Why are they using polarization in NorthAmerica is beyond me: polarized
filtering is *not* a Status T specifcation, pounds David McDowell.
> I've also found that X-Rite 500 series
> spectro-densitometers will read about .10 higher than my SpectroEye
> even without polarization.
Well that's interesting. You must be using a T-Ref or something similar to
make that determination? I find that ALL instruments, regardless of makes,
have to perform equally on this set of certified patches, using Status T !!
If they're not we're in trouble. I keep hearing references to ASTM 308
computation adopted by X-Rite as compared to GMB using something different
in the process of capturing the spectral information from a sample as the
root of this problem, but I confess I never needed to push this any further.
> Personally, I think inter-instrument (or
> inter-vendor?) agreement is the industry's dirty little secret.
And I thought that gray balance was the holy grail of color management :(
> I've
> even been to shops that have a mix of Gretag and X-Rite units of
> different vintages (X-Rite 528 and older 408s for example or perhaps a
> SpectroEye and D19C) and NONE of the units will agree within .05 of
> each other even after careful calibration.
Well that's a fantastic note. And I'd be curious to see what all these
instruments would have say on a fresh T-Ref. To me, that's the best standard
reference material out there for graphic arts densitometry.
> So, for better or worse, my
> SpectroEye becomes the reference unit at least while I'm on-site.
As long as your Spectro-Eye does not decide to go south...
I'm having difficulties with some of my instruments these days. Enough so
that I feel the acute need to have some extremely stable standard reference
color material, like a BCRA tile, to assist me in determining *when* my
instrument's calibration starts to drift and whether or not I can trust it
at all for making profiles. I'm familiar with the "Lab-Ref", also made by
IDEAlliance, but I'm shying from it for the moment. I'd rather find some
material I could equally read with all my instruments. Otherwise, over time,
there is no telling which of these intruments is telling the truth since
they'll always pass their respective calibration. And doesn't THAT make a
whole world of difference in the final analysis.
> Since
> my SpectroEye TENDS to read lower compared to other instruments, I'm at
> least confident that, even after dryback, we'll have densities that are
> pretty close to the targets as measured by other instruments.
How old is your SpectroEye, if I may ask?
> Later,
> Terry
Regards,
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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