Re: SWOP Proof Certification, TRxxx Characterization Data
Re: SWOP Proof Certification, TRxxx Characterization Data
- Subject: Re: SWOP Proof Certification, TRxxx Characterization Data
- From: Klaus Karcher <email@hidden>
- Date: Wed, 29 Oct 2008 18:10:48 +0100
Roger Breton wrote:
...I don't agree this cannot be
carried on to users in the field. With instrument's quality where they
are
today, EyeOnePro's grade and the like, I don't see why adopting these
requirements would create havoc.
Mike Eddington wrote:
Well, havoc might to too strong a word. The fact is that many users can
and do hit the tolerances of the Proofing System Certification with ease
(ave. 1.5 dE76, etc), however, if a common "master" instrument was used
to measure them all and judge them pass or fail, many would fail. Of
course, there isn't such a "master" instrument (so who's right?), and
taking the i1 as per your example, differences between rev levels can be
significant. My rev A and rev D units measure an average 1.5 dE76
apart...certainly not close enough to be interchangeable with tight
proofing tolerances.
You are absolutely right: I guess we have to live with the dilemma that
the tolerances are too large for demanding, color-critical jobs but
already too tight to be measured dependably with nowadays instruments.
Berns[1] refers to ASTM E 1345: "A statistical rule of thumb states that
the uncertainty due to measurement should be less than 10% of the total
uncertainty in manufacturing". When we use an Delta H = 2.5 for the max
acceptable color distance of the primaries, we should make sure that the
measurement uncertainty is below Delta H = 0.25 for this criterion --
fairly unrealistic even with two instruments of the same brand, model
and revision!
Fogra / BVDM (the German printers association) has a quite clear
position on how to deal with this dilemma:
Suppose a client sends a contract proof and data to the printer. The
printer checks the proof with his instrument and confirms that it is
valid (i.e. within the allowed tolerance) then *this proof* is part of
the contract between the printer and his client and *this proof* is the
visual and colorimetric reference for the print job, *not* the ISO
12647-2 aims!
When the printer evaluates the supplied proof and concludes that it is
*not* valid, he has to inform his client about the problem *before* he
starts printing.
Unfortunately this policy does not find enough expression in the current
BVDM publications (MediaStandard Print, PSO) IMHO -- one has to read
between the lines to get it. This cause confusion sometimes and many
printers are proud to print according to ISO 1247-2 but forget to look
at the client's proofs.
From my experience with a company that provides proofs, printers often
have there own targets and tolerances...some intelligently based, using
dE94, others requesting legacy density/dotgain, and others making up
there own. Its not uncommon for me to have a conversation(or three) with
the printer to agree on required metrics and discuss instrument agreement.
From my experience, most of the clients and printers won't be able to
determine usable (i.e. workable and reliably measurable) tolerances --
simply for the lack of necessary background knowledge.
Boy! The people who download the colorbar and ponder what to do with it
should consult a guys like you, Mike -- I know I would ;-)
I charge CHF 740. ;)
sluttish price dumper! ;-)
You would think that the ADS would go as far as defining a metrology
framework including how to measure the target, with what instruments,
and so
forth. Didn't X-Rite sold more DTP41's for all the ADS of this world than
any other instrument manufacturer?
Perhaps that's true. I know that for the 2007 proofing roundup a DTP-70
was used for the judging, and of course, all the venders then used
DTP-70s to generate their profiles. The user submissions used any and
all instruments, and of course, their results varied that much more (for
that and other factors).
What about ISO-9001 quality control
programs? Can't we expect people send in their instrument once a year for
re-certification? Wouldn't that lend some credence to ADS? And bring back
some needed inter-instrument agreement?
I honestly don't think so. Re-certification is certainly not a bad
thing, but I disagree that it addresses instrument agreement issues.
Gauging the performance of several of our "certified" devices to each
other, I am less then impressed. Moreover, instrument agreement on BCRA
tiles doesn't necessarily correlate to agreement on real world substrates
I think there is an advantageous alternative to factory or laboratory
re-certifications: periodic round robin tests! (i.e. one gets some
probes quarterly or monthly by mail, measures them, loads up the results
to a web server, sends back the probes and gets a detailed report after
the test round is finished).
Round robin tests have many advantages:
- one has not to send in the instrument
- one can use realistic measurement conditions
(realistic probes, scan mode instead of spot measurements,
measurement in ordinary working environment by ordinary operators --
not under laboratory conditions)
- one can compare one's own results with competitors anonymously
- more frequently tests are possible
- they are less expensive
I am working on offering (organizing and evaluating) such tests on a
commercial basis and hoped to be able to offer a first beta test yet
this year but I'm afraid I'll need more time.
See also my posting on this topic in July:
<http://lists.apple.com/archives/colorsync-users/2008/Jul//msg00044.html>
I think in the light of Danny Rich's paper[2] it's no exaggeration to
say that the pre-press/press industry badly needs more measurement
device monitoring. Round robin tests can be a practicable way to
accomplish this task as other industry segments, laboratories and
services like <http://collaborativetesting.com/> already have demonstrated.
Klaus Karcher
-----
[1] Roy S. Berns: Billmeyer and Saltzman's Principles of Color
Technology, 2nd Edition, Chapter 3E
<http://www.amazon.com/Billmeyer-Saltzmans-Principles-Color-Technology/dp/047119459X>
[2] Danny C. Rich: The Effect of Spectrocolorimeter Reproducibility on a
Fully Color-managed Print Production Workflow (CGIV 2008 proceedings --
unfortunately not yet listed on <http://www.imaging.org/>)
--
Klaus Karcher * Eichenallee 18
26203 Wardenburg * Germany
Tel. +49 441 8859770
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