Hello to the PDF specialists,
I have a customer, who wants to be ISO 12647-8 certified by FOGRA with a high end CMYK Inkjet solution.
The certification includes the PDF/X-Ready output suite 3.02 which contains the patch GWG2.0 Spot to CMYK overprint.
With the current RIP version this patch shows crosses in a different green, than the rectangles.
The GWG readme for this patch states:
A faint ‘X’ in slightly darker green may show in all of the
tests; this is acceptable behavior in this patch. Only a clearly
visible X indicates an incorrectly rendered patch. Please see
example on the first page of this README file.
This patch appears to be a simple patch, and should be
rendered without fail on its own. It is, however, possible that
the amalgamation of this patch with other patches may very well
lead to problems. There are several cases in which objects set
to overprint using Spot colors can prove to create some advanced
problems. For example, If you simulate Spot colors for proofing
or commonly convert Spot colors to CMYK this patch can be used
to highlight potential errors in your working practices. Use
this patch along with patch 10 —Spot to CMYK conversions for
testing Spot color simulation.
If I open the patch in Acrobat Professional and activate
overprint simulation I don´t see any crosses (expected behavior).
In output preview (german Ausgabevorschau) I measure, that the
overprinting objects have only a tone value of 1% (in the top row
CMYK overprints spot, in the bottom row spot overprints CMYK). The
object inspector does not show an alternate colorspace for the
spot color objects in GWG green.
The standard output intent for the patch is ISOcoatedv3_300_eci.icc If I change the simulation profile in Acrobat Pro to quite different printing conditions like e.g. newspaper or Epson inkjet profiles, all patches stay perfect green - no crosses.
I talked with the RIP vendor for the solution and also they are
surprised. In 2016 internal test showed perfect patches with no
visible crosses. Now we see two different greens. Concerning the
GWG readme, this is an acceptable behavior.
Both the customer, the RIP vendor and I want to understand, what
is happening here. Between 2016 and today, the RIP solution got an
update of the Adobe PDF Print Engine (APPE). As the printer uses
only CMYK for printing, the RIP must convert overprints between
spot and CMYK to CMYK only.
I have following questions to the PDF-specialists in this list:
1) Is it possible, that an APPE update changes the behaviour how
overprints between spot and CMYK are rendered to CMYK only ?
2) Why i don´t see an alternate colorspace for GWG green in the
object inspector of Acrobat Pro ?
3) Why I don´t see slight crosses in Acrobat Pro, when I change
the simulated print condition ?
4) Does GWG has an mailinglist to aks such questions ? (I didn´t
found it on the GWG website...)
Thank you for any hints
Jan-Peter
-- Homann colormanagement tel: +49 30 611 075 18 Jan-Peter Homann mob: +49 171 54 70 358 Herzbergstr. 55 www.colormanagement.de 10365 Berlin mailto:homann@colormanagement.de