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