Re: The GRACoL method
Re: The GRACoL method
- Subject: Re: The GRACoL method
- From: Don Hutcheson <email@hidden>
- Date: Sun, 04 Feb 2007 14:20:35 -0500
- Thread-topic: The GRACoL method
On 07/02/03 15:02 Roger Breton <email@hidden> wrote:
> Hi Dan,
>
>> The easiest path to G7 is using an uncalibrated platesetter (can be done with
>> film workflow too).
>>
>> Most CTP RIPs only have one area to put in a calibration curve. Agfa work a
>> bit different as the plates are calibrated/linearised on their exposure
>> box¹.
>> In this case it makes no difference if there is a curve there or not.
>>
>> Once you print and read the P2P23xn test chart, you will have the values to
>> use in the RIP.
>>
>> Dan Wilson
>
> I'm just curious what kind of TVI you end up with once calibrated with G7?
>
> I understand the gist of the method does not revolve around TVI -- far from
> it -- but, once a press is in that golden G7-calibrated state, which is, for
> all intents and purposes, according to humble tests, the same as linearizing
> a proofer for gray balance (ends up with linear L* between dMax and dMin
> with respect to CMY and K), what happens with the zillions of CMYK images
> that are separated for the standard, pre-SWOP11 TVI aims, when they hit the
> press: are they going to register lighter, darker or what?
>
> There are still a lot of folks who are cranking out separations from chromes
> on well-maintained drum scanner, folks who voluntarily avoid digital
> photography, for good or bad, or who still regard film as the superior
> reproduction medium.
>
> Roger Breton | Laval, Canada | email@hidden
> http://pages.infinit.net/graxx
Hi Roger,
Good question. The short answer is that files separated to traditional SWOP
TVI numbers should look "normal" on a G7-calibrated press, because the G7
NPDC (Neutral Print Density Curve) closely mimics the NPDC of TR001, which
is the basis of Adobe's US Web Coated (SWOP)v2 profile, and most proofing
and scanner setups.
One of the primary goals of the G7 method was compatibility with existing
files and standards. We wanted to up-date the SWOP and GRACoL
specifications, and interpretation of ISO12647-2, to reflect the subtle
changes in how a typical press prints today, with CtP plates, compared to
fifteen years ago with film-based plates.
Although it sounds radical at first, G7 is just evolution, not revolution.
Recent research by SWOP and GRACoL shows that today's CtP presses tend to
produce higher densities but lower TVIs, which results in a similar overall
NPDC curve from white paper to mid-tones, compared to traditional printing.
This explains why the new G7 curve fits the old TR001 data very well. The
main difference between the new G7-based SWOP2006 data set and the venerable
TR001 data is a slightly fuller shadow curve, which if anything gives images
more "snap", which nobody seems to complain about.
Note that both the new SWOP2006 and GRACoL2006 characterization data sets
are based on a common NPDC curve and identical ISO 2846 inks, with just
slight differences in ink densities, paper brightness, and paper color.
This means that not only is a G7-calibrated press or proofing system
compatible with "traditional" SWOP separations, but also separations made
for SWOP2006 or GRACoL2006 are effectively interchangeable - a major benefit
when 90% of today's CMYK images are separated without knowing which type of
press they will be printed on.
I hope this clarifies things.
Regards,
Don
******************************
Don Hutcheson, (GRACoL chair)
HutchColor LLC
Phone: (908) 689 7403
Mobile: (908) 500 0341
E-mail: email@hidden
******************************
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