Re: Newsprint G7 calibration
Re: Newsprint G7 calibration
- Subject: Re: Newsprint G7 calibration
- From: Roger Breton <email@hidden>
- Date: Sat, 24 Mar 2007 11:16:33 -0400
I did use the latest of everything. Believe me. Freshly downloaded off
Gracol's site. And, I always export as CGATS out of ColorPort. I, too,
realize the spectral data is useless for IDL as we know that all
"densities" reported are derived out of XYZ and not StatusT, and those
"densities" don't even enter into the G7 calculations anyway. BTW, what good
is it to have "densities" displayed in the interface when they don't follow
long time established industry conventions like ANSI and ISO StatusT? Might
as well not display the information at all, it does more harm than good,
IMO.
Anyhow, for this test, everything was plated as is. Meaning, the 50% dots in
the P2P23xn TIFF file ended up as reading 50% on the plate with the plate
dot meter. Nothing else I can do. Except, I noticed, that dot percentages
below 50% were increasingly lower than linear and dot percentages above 50%
became increasingly higher than linear. BUT WE ARE TOLD IN THE "G7 How To"
that the plates don't have to be linear to begin with. So I did not bother.
I suspect this could have something to do with the strangeness of my
results. But hey, I'm being a good color citizen and play by the G7 rules.
Having said, I, too, have been tinkering with the idea of modifying the
P2P23xn target to compensate for some flaws I see in its design but I have
not found the time to do that. Of course, I'll be interested to look at your
target at some point.
> If you're going to have a chance to run the test again,
I'll have to -- no choice :(
> I'd be happy
> to send you the target that I use all the time. It's a bit wider and
> shorter (5.5" x 9") than than the standard P2P target but it works
> well with the DTP70 (I sized it so it's no taller than the width of a
> standard DTP70 IT8.7/4 chart - makes for easier cutting up of the
> press sheet!).
And says that the standard P2P23xn target worked flawlessly on coated
papers, BTW.
> There WAS a problem a while back with the charts being a bit to
> narrow for the DTP70 causing measurement errors but that was
> supposedly fixed with the P2P23xn targets.
Hmmh. If anyone wants to take a look at my printed targets and see what they
can learn from them, just drop me a note offlist.
> Nonetheless, I decided to
> use the supplied reference data and build my own P2P23 targets. I've
> been using this target since about October of last year and on at
> least 8-10 G7 press calibration jobs and it's been working fine.
Awesome.
> FYI, I personally don't feel that the IDEALink software compensates
> enough for low Dmax printing conditions such as uncoated offset or
> newsprint that it really delivers on the promise of a decent visual
> match between different print conditions but that's just my opinion.
I'm told that IDL strictly embodies Don's calculations.
> The result to my eye is too dark overall and doesn't move the HR
> point enough for low Dmax printing.
"Low Dmax printing" like newsprint?
Interesting. You echo a colleague of mine's very observations.
> Personally, I wish the HR
> aimpoint was adjusted relative to the 100% CMY Dmax (possibly based
> on a linear L* approach).
But, Terry, haven't you found that the adjusted CMY curves makes the
selected CMY combinations __linear__ with L*??? So, far, that's the results
I've been getting on a number of G7 trial runs, regardless of the substrate
or printing technologies: to me, what the G7 method does is simply linearize
an output system with respect to CIE L*!!! When I plot the before and after
curves of input dot percentages versus output L* that's what I invariably
obtain. It can't be just a series of flukes?
> As of right now, it does SOME adjustment
> but not enough in my opinion.
Right. We have to abide by the rules of Gracol now.
> Later,
> Terry Wyse
Regards,
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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