Re: tools for building device links (was "Proper Gamut Mapping")
Re: tools for building device links (was "Proper Gamut Mapping")
- Subject: Re: tools for building device links (was "Proper Gamut Mapping")
- From: Terence Wyse <email@hidden>
- Date: Mon, 17 Dec 2007 09:03:07 -0500
Thanks Elie,
I know the author of the report and it would make sense that ORIS
Color Tuner was the RIP platform.
So when the author states that the samples were converted "to the
color space of the Epson 4000", does he mean its "natural" or raw
color space (full gamut), an ink-limited and linearized color space
(full gamut but "well-behaved") OR had the Epson 4000 been profiled
and iterated to match SWOPv2 (TR-001?) within ORIS and that's what the
author was referring to as the "color space of the Epson 4000"?
Not to take anything away from your products (I think they are
excellent and one of only two such products that I recommend) but I
think there's enough holes in that report to bring it under question.
Regards,
Terry Wyse
On Dec 17, 2007, at 3:16 AM, ELIE KHOURY wrote:
Terry, I was not involved in the tests but I am nevertheless sure
that a CMYK RIP was used to drive the EPSON. I believe it was CGS RIP.
Elie
*****************************************
On 17 déc. 2007, at 00:16, Terence Wyse wrote:
On Dec 16, 2007, at 3:58 PM, Roger Breton wrote:
You need the link to the article in question. I have a hard copy
which Elie
distributed at the GATF CMS Conference, last week. Very
convincing. So many
ways to skin a cat (sorry Marco).
I believe there's more than a few flaws with this report although
this is the first time I've heard of it or read it. My comments
below are after a quick skimming of the report.
The first thing I noticed was there didn't seem to be any mention
of what profiling package was used to create the destination
profiles used to build the links in the first place. The only
mention was of the source profile used, USWebCoated(SWOP)v2. A few
reasons why I believe this is important:
1) The "quality" or colorimetric accuracy of a device link profile
is somewhat subject to the raw profiles used to build the link in
the first place. I think some initial testing should have been
performed to ascertain what combination of source/destination
profiles introduced the least colorimetric error into the profile
chain. I suppose as long as all the device links were built using
the same pair of source/destination profiles, maybe this point is
moot but I can imagine that some device link applications would
perform better using one pair of source/destination profiles vs.
another, even though the profiles could've been created from the
same data set. As noted in the report, differences of .50 delta E
or less are probably meaningless. In the colorimetric comparison, I
think a single max dE is meaningless as well (a single poor max dE
value could be printer variation as much as the device link).
Average dE is OK, but I'd rather see a "worst 10%" value. How a
profile conversion handles the 10-20% most difficult colors/patches
would be very telling I think, even more so than average dE.
2) Ink consumption report. I think it's hardly fair to compare
various device link applications that rely on the destination
profile for "ink savings" (GCR) as opposed to those link apps that
can override the destination profile separation settings. Granted,
having the ability to alter the ink savings/GCR directly within the
device link application is a nice feature but that doesn't
necessarily mean that other device link apps could not have
improved upon their ink consumption figures if the destination
profile had used more "aggressive" GCR settings. I've done a bit of
evaluation of ink savings myself and can tell you that the K
generation used in the destination profile has quite an impact on
the resulting ink savings. But to be fair, the ink savings that
result from those device link apps that offer GCR controls appears
to be substantially greater than those link apps that relay soley
on the destination profile's separation settings, at least in my
testing.
3) "Purity" tests. Apparently this was tested using an Epson 4000
as the output device but using USWebCoated(SWOP)v2 as source. As we
all know, the pure inks of almost any inkjet device that comes to
mind can be anywhere from slightly different to wildly different
than an offset press. Testing the preservation of pure ink colors
from an offset press profile to an inkjet printer would result in
fairly extreme colorimetric errors I would imagine. I fail to see
where a test of preservation of pure ink solids or tints using the
parameters outlined in the report would have any meaning at all.
Preservation of pure inks is really only relevant when repurposing
from press-to-press. There's precious few instances where
preserving pure inks from a press to an inkjet device is desirable.
Other questions:
The author of the report only stated that the conversion was
performed to the "color space of an Epson 4000" via the Apple CMM.
Does this mean the entire test was NOT peformed via a CMYK RIP but
was instead printed via the Epson OS driver? If so, then how was
this testing CMYK-to-CMYK conversions since an Epson 4000 profiled
via the driver must be done in RGB? A better test perhaps would've
been to perform this via a CMYK RIP that had some basic
linearization and ink limiting features but where the conversion
itself was performed in Photoshop instead of the RIP. I can imagine
performing such a test with, say, a ColorBurst RIP or even a GMG
RIP which offers excellent calibration features but can have
profile conversions disabled. This would be a good platform from
which to generate very stable/consistent output from the inkjet
printer.
The colorimetric comparisons and "round-tripping" of profiles was
performed using an application not publicly available as far as I
know. Knowing the source of this application, I'd be reasonably
sure that it's a high quality evaluation software but it prevents
any sort of independent verification of the tests results. I'd be
much more comfortable if the author had used "recognized"
applications such as ColorThink Pro, LOGO ColorLab, X-Rite Measure
Tool, etc. I would've preferred that the author had used a more
"mainstream" application rather than a custom application that
could've quite possibly introduced errors of it's own.
Regards,
Terry Wyse
_____________________________
WyseConsul
Color Management Consulting
G7 Certified Expert
email@hidden
704.843.0858
http://www.wyseconsul.com
http://www.colormanagementgroup.com
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