Hello Florian,
Thanks for your response to my email.
You said:
> Given the CIELAB measurements of 50% yellow
> are blueish compared to the aim values (e.g.
> due to a blueish paper tone or blueish yellow
> ink) - how should a printer correct this?
> The linkage of density and CIE L* does not
> work as well - even substantial increase/
> decrease of yellow density almost does not
> change the L* value.
> In case of TVI differences process control
> is clear (increase/decrease density, make new
> plates, etc.)
I am sorry; I guess I didn't explain the idea clearly. The proposal was to use dE (which is derived from the Lab measurements) just as you use TVI estimates today - purely as a means of process control.
Today instruments measure the density of the paper, the density of the solid and the density of a tint and using an approximate calculation estimate %dot for that tint. Printers then compare the '%dot' value currently achieved against their aim '%dot' value.
In the proposed scheme instead of measuring density, instruments would measure Lab of the paper, Lab of the tint and possibly Lab of the solid. >From these measurements the colour difference (dE) from the paper is calculated - this could be scaled so that the solid becomes '100'. Users in this case would compare their measured value with the aim value and adjust the process as they do today.
In addition to this measure, the solids would be measured using Lab which ensures that problems of different inks and ink contamination can be detected [which cannot be seen using a densitometeric approach].
Best regards,
Craig Revie
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Hello Olaf,
Craig:
> > There may also be better measures for the future
> > than that of TVI, for example a measure of dE
> > relative to the paper. This measure is available
> > from the ICC profile.
Olaf:
> How could this be used to adjust tint values of a
> given color channel?
Today we estimate TVI using a density measure and a very approximate method to estimate actual area coverage (%dot). Printers know that a 50% tint should 'gain' on press and actually 'measures' (say) 68%.
Instead of the density-based measure we currently use I was suggesting that for each tone scale we should measure Lab for each tone scale and from this calculate dE relative to paper each tint. Printers would then make sure that the dE measure was within the specified tolerance for the print process - in the same way as they control TVI today.
This process has a number of advantages [thanks to Mike Rodriguez of RR Donnelley for suggesting some of these]:
(1) It removes some of the inter-instrument variability that I understand to be present between densitometers from different manufacturers.
(2) It is a measure that links process control and colour management as the aims are directly available from the ICC Profile.
(3) It's a very practical way to introduce colorimetry into production Processes.
(4) It allows stable normalization to substrate; TVI (i.e. relative density) is very sensitive to paper measurement error which is a problem even if densitometers are consistent.
(5) The measure is more proportional to visual differences, e.g. large density differences near the solid give relatively small visual or dE differences.
As Bob Hallam of Quebecor has pointed out this new measure will be very unfamiliar to printers and we may need to have some kind of mapping from the old approximations to the new more precise colorimetric measure.
I would be very interested in hearing both positive and negative comments on this concept.
Best regards,
Craig Revie
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Hi Olaf,
I have been looking at your presentation and look forward to discussing
it in further detail next week at the ICC meeting. In the meantime I
have some simple questions:
(1) You mention as part of your proposed solution:
"output intent must consist of
- CMYK output profile
- information about tone value increase"
What information do you think the tone value increase would add to that
already present in the ICC profile? Have you considered the possibility
that TVI can be estimated from the ICC profile? There may also be better
measures for the future than that of TVI, for example a measure of dE
relative to the paper. This measure is available from the ICC profile.
This would mean that PDF/X-3 documents already meet this part of your
requirement.
(2) The addition of a new rendering intent [Maintain Colorants] is an
interesting idea but I think needs further definition.
It is clear how the 'Maintain Colorants' intent should map colours that
use only a single colorant but how should C=M=50% be mapped? And what
about CMYK [20,30,10,20]?
Best regards,
_Craig
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Dear members of the bcm mailing list,
yesterday I have given a presentation at a workshop at BAM in Berlin that
discussed some issues with regard to use of ICC color management in the
real world of the graphic arts industry. Please consider it as a starting
point to get the discussion going about issues with and limitations of
current implementations and uses of ICC based color management.
In the coming weeks I will try to develop my thoughts further and will
put togeteher a paper that explains my view more explicitly than is
possible with a couple of slides. Nevertheless the attached slides
hopefully will trigger some discussion.
Regards,
Olaf
--
Olaf Druemmer | Managing Director
callas software gmbh | Schoenhauser Allee 6/7 | Berlin | Germany
Tel +49.30.44 39 03 10 | Fax +49.30.4 41 64 02
o.druemmer(a)callassoftware.com | www.callassoftware.com
Dear members of the bcm mailing list,
yesterday I have given a presentation at a workshop at BAM in Berlin
that
discussed some issues with regard to use of ICC color management in the
real world of the graphic arts industry. Please consider it as a
starting
point to get the discussion going about issues with and limitations of
current implementations and uses of ICC based color management.
In the coming weeks I will try to develop my thoughts further and will
put togeteher a paper that explains my view more explicitly than is
possible with a couple of slides. Nevertheless the attached slides
hopefully will trigger some discussion.
Regards,
Olaf
--
Olaf Druemmer | Managing Director
callas software gmbh | Schoenhauser Allee 6/7 | Berlin | Germany
Tel +49.30.44 39 03 10 | Fax +49.30.4 41 64 02
o.druemmer(a)callassoftware.com | www.callassoftware.com
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