Re: Gracol press runs
Re: Gracol press runs
- Subject: Re: Gracol press runs
- From: Don Hutcheson <email@hidden>
- Date: Mon, 05 Sep 2005 12:09:43 -0400
Roberto,
Some quick answers to your questions;
> On reading a press release from a year ago, regarding the press run at
> Sandy Alexander to verify DTR004 and from which additional Gracol v6
> data was derived, I found the following:
> "Larry Steele of RGB Metrology conducted the press side measurements
> for GRACoL and said that the initial results indicated that this was a
> truly representative GRACoL press run close to the center of
> conditions. "This was also one of the more consistent printing
> conditions that we have experienced both throughout the sheet and from
> run to run" said Larry Warter of the GRACoL Committee. Don Hutcheson
> of the Manhattan Project added "the approach used to create the plates
> produced very smooth curves that should be ideal to facilitate future
> color managed printing under production conditions"
>
> So couple of questions arise:
> 1) which was that approach used to create the plates? anything special?
The process involves two press runs (or proofs, if you are calibrating a
proofer);
(1) a "calibration run" made with "raw", or "un-calibrated" CtP plates, run
to nominal SIDs of approximately 1.5 C, 1.5 M, 1.0 Y, 1.85 K, (some latitude
is allowed in SIDs) and
(2) a "characterization run" made from CtP (or proofer) curves based on the
calibration run, and made to the same densities.
The calibration run should ideally be engineered to produce a nominal
mid-tone CMY gray balance of 0.0 a* and -2.0 b* in a 50c, 40m, 40y patch, -
presumably by adjusting solid ink densities, packing, impression, ink
viscosity, etc. If this is not possible (for example in a fixed laminate
proofing system) or not desirable, mid-tone gray balance can be adjusted
instead using separate CMY CtP (or proofer) curves.
>From the calibration run GRACoL uses a formula which calculates two ideal
Print Density Curves for (1) a neutral-gray CMY scale and (2) a black ink
gray scale, based on data measured from the "P2P 14" target, available free
at ...
<http://www.hutchcolor.com/Targets_&_images_to_go/P2P_strip.hqx>
The formula is currently proprietary and still undergoing final tweaks, but
the resulting curves will be made available free as PDF images upon release
of GRACoL7. For the GRACoL press runs and subsequent data analysis we are
using an Excel Workbook which automatically calculates Print Density Curve
and gray balance correction values. This Workbook may be available
commercially, but no idea on price yet.
> 2) if such a press run is so representative of Gracol (from the
> wording it seems better than previous ones), does that mean it's
> measurements would provide a better reference than DTR004 itself?
Yes. Some problems were discovered in the DTR004 data, primarily in curve
shape and saturated ink hues, and the Sandy Alexander run solved a lot of
these problems. However since that run, GRACoL has further refined the
target curves, hence the Sandy data differs slightly from the final GRACoL 7
data. Nevertheless the Sandy sheets and data are a good stop-gap between
the old DTR004 and the new GRACoL7 Data.
> will DTR004 be replaced soon?
Almost certainly, but see "DTR004 REPLACEMENT?" below.
Characterization data is being analyzed from the eight press tests GRACoL
made in 2005, along with the Sandy Alexander run from 2004, and the already
existing FOGRA data, upon which ECI's "ISO" profiles are based, and also
some commercial characterization data from Japan.
>From this pool of data sets, a combined data set will be produced by a
combination of averaging, modeling and smoothing, which represents as
closely as possible the appearance of a typical CtP- based commercial press
using standard ISO inks and grade 1 paper, regardless of where in the world
it is operated. This process is a joint exercise of GRACoL and the Printing
Across Borders initiative (www.printingacrossbrders.com). This data set
will hopefully represent a democratically- and scientifically- optimum
"Reference Commercial Print Appearance" data set that everyone agrees is not
just European or American, or Asian, but truly international.
Estimated release date for this data, tentatively called "GRACoL 7
Commercial Data", is January 2006. Beta sets may be available earlier.
DTR004 REPLACEMENT?
The GRACoL 7 Commercial Data will almost certainly be considered a
replacement for DTR004, but due to formalities I cannot confirm what it will
be officially called, or when it will be officially accepted.
I seldom have time to respond to this list (currently working 80+ hours a
week just trying to get the data right), but you can stay on top of
GRACoL7's progress at www.gracol.org
Thanks for your interest.
Don
On 9/5/05 1:03 Roberto Michelena of email@hidden wrote:
> (question to Don Hutchenson but cc'd to the list as it should be of
> general interest)
>
> Don,
>
> On reading a press release from a year ago, regarding the press run at
> Sandy Alexander to verify DTR004 and from which additional Gracol v6
> data was derived, I found the following:
> "Larry Steele of RGB Metrology conducted the press side measurements
> for GRACoL and said that the initial results indicated that this was a
> truly representative GRACoL press run close to the center of
> conditions. "This was also one of the more consistent printing
> conditions that we have experienced both throughout the sheet and from
> run to run" said Larry Warter of the GRACoL Committee. Don Hutcheson
> of the Manhattan Project added "the approach used to create the plates
> produced very smooth curves that should be ideal to facilitate future
> color managed printing under production conditions"
>
> So couple of questions arise:
> 1) which was that approach used to create the plates? anything special?
> 2) if such a press run is so representative of Gracol (from the
> wording it seems better than previous ones), does that mean it's
> measurements would provide a better reference than DTR004 itself? will
> DTR004 be replaced soon?
>
> From latest news it would seem that Gracol is moving faster than ECI
> or Fogra (not to say ISO!) nowadays... quite a change from years ago!
> while at the end everything will be the same standard (we all hope...
> go PAB!!) ; however I wonder how fast are printers in the USA willing
> to implement new standards... in some european color site (I don't
> recall if ECI, Fogra, or maybe even Ifra) I have recently read
> something like "germany: all printers will adopt the new standard on
> xx of xx, 2005" ; can you imagine that?
>
> -- Roberto Michelena
> Infinitek
> Lima, Peru
******************************
Don Hutcheson
Hutcheson Consulting
(Color Management Solutions)
Washington, NJ 07882 USA
email@hidden
******************************
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