I agree that problems such as this might not be clearly evident in the
final prints, as the crux of this issue occurs at the separation
stage. The press can be reproducing the CMYK values superlatively
toward Fogra39 and/or the proof, but they may not be the same CMYK
values we might have had using a different profile for separation
(i.e. different gamut mapping), and any issues of undesirable
purplish-blues due to the separations may have been corrected by press
time. I'll also agree that the purplish-blue issue is most apparent
for extremely out of gamut blues, but can be witnessed in converting
real world RGB images as well. I don't wish to blow this issue out of
proportion however. Suffice to say that gamut mapping is subjective,
and the end user would do well to analyze a profile prior to
incorporating it into a workflow to ensure it meets their needs.
Michael Eddington
QA Manager/G7 Certified Expert
North American Color, Inc.
www.nac-mi.com
www.nac1to1.com
www.photo360.com
------------------------------
Message: 5
Date: Tue, 5 Feb 2008 09:04:50 +0100
From: "Bestmann, Guenter RD-PT23" <Guenter.Bestmann(a)heidelberg.com>
Subject: Re: [ECI-EN] RGB to CMYK
To: <eci-en(a)lists.callassoftware.com>
Message-ID:
<E30A95A7B013094997CABEC3F488573CFF8637(a)wiems02014.ceu.corp.heidelberg.com
Content-Type: text/plain; charset="iso-8859-1"
Dear all,
the profile ISOcoated_v2_eci was build with Heidelberg's PrintOpen
5.2. Before publishing the profile a lot of tests were made. ECI
made also some comparisons with profiles from other vendors. The
final decision was for the PrintOpen profile because from an overall
point of view this profile has some more advantages than
disadvantages with respect to other profiles.
I will not discuss the advantages and disadvantages with respect to
profiles of other vendors.
In normal circumstances you will not find any problems when printing
with this profile. Problems may (but must not) arise when separating
extremely out of gamut RGB-colors, for example an AdobeRGB blue with
RGB = 0/0/255. Mapping of extremely out of gamut colors in this area
may cause a (slightly) purplish blue. In addition to the gamut
mapping this purplish blue depends on the ink trapping too.
I never saw printed samples which are not useable or sellable when
a) printing to the ISO standards colorant values and tvi curves and
when b) preparing and separating carefully images or graphics before
printing.
The rumors about quality problems with ISOcoated_v2_eci and other
ECI profiles are from other profile vendors and from people looking
only at separations and previews and not at the final prints.
Heidelberg uses this profile together with other profiles build with
PrintOpen in their show rooms and education centers. If there are
real problems with the separations then we were the first to solve
these problems. The purplish blue for extremely out of gamut colors
was corrected in the new version of PrintOpen available soon.
Kind regards,
Guenter Bestmann
Dr. Guenter Bestmann
Research & Development
Heidelberger Druckmaschinen AG
Dr.-Hell-Strasse
D-24107 Kiel
E-Mail: guenter.bestmann(a)heidelberg.com
Tel: +49-431-3863887
Fax: +49-431-3863287