Hello Craig,
Hello Mike,
Please allow my jumping in on Mike's five points regarding advantages
of colorimetric process control.
Based on my experiences except for point 5 the opposite is the case:
(1) It removes some of the inter-instrument
variability that I
understand to be present between densitometers from different
manufacturers.
Inter-instrument agreement of color measurements shows noticable
differences in the case of using different manufacturer's devices.
There is a number of evaluations prooving that issue (Fogra, test at
Digital Proofing Forum 2004, practical tests of user's)
Inter instrument agreement is quite good regarding tone values (based
on e.g. POL filter use/absence there are different density values but
these are not relevant in tone value calculations).
(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.
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.)
(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.
I.o.w. switching colorimetric
measurements from absolute white point
calibration to substrate white point calibration - right?
(5) The measure is more proportional to visual
differences, e.g. large
density differences near the solid give relatively small visual or dE
differences.
Ok - but isn't that a prepress issue?
It's up to the originator of an image (photographer, prepress, design)
to adjust color and gradation. That works very good using Photoshop's
working spaces and viewing on a calibrated and profiled monitor.
Calcualtion of respective cmyk values is a matter of ICC profile
quality. If the printer matches the process aims of the profile (TVI,
CIELAB of solids, mid tone spread) his print will match the intended
gradation.
Best Regards,
Florian
Am 27.04.2005 um 16:54 schrieb Craig Revie:
> 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
>
> -----------------------------------------------------------------------
> -----
>
> CONFIDENTIALITY AND DISCLAIMER NOTICE
>
> This message and any attachment is confidential and is protected by
> copyright. If you are not the intended recipient, please email the
> sender or telephone +44 (0)1442 213440 and delete this message and any
> attachment from your system. Dissemination and or copying of this
> email is prohibited if you are not the intended recipient.
>
> We believe, but do not warrant, that this email and any attachments
> are virus free. You should take full responsibility for virus
> checking.
>
> No responsibility is accepted by FUJIFILM Electronic Imaging Limited
> for personal emails or emails unconnected with FUJIFILM Electronic
> Imaging Limited's business.
>
> -----------------------------------------------------------------------
> -----
>
>
> _______________________________________________
> bcm mailing list
> bcm(a)lists.callassoftware.com
>
http://lists.callassoftware.com/mailman/listinfo/bcm
>
>
--
Florian Suessl | Director Technology
MetaDesign AG | Leibnizstrasse 65 | 10629 Berlin
+49 30 59 00 54 246 | fax +49 30 59 00 54 111
fsuessl(a)metadesign.de |
http://www.metadesign.de