Re: Scan Backs and Painting Copies
Re: Scan Backs and Painting Copies
- Subject: Re: Scan Backs and Painting Copies
- From: Stefan Fiedler <email@hidden>
- Date: Thu, 18 Jul 2002 14:19:23 +0200
Hi
This is my first posting to the list, being an imaging science student
preparing a dissertation on digital reproduction of paintings. I understand
that the ccd's in scan backs are often based on scanner technology, and as
such are optimised for cmy (dyes) color accuracy, not rgb. This would mean
good color accuracy for photographic artwork, but not for pigments. An area
array ccd in a digital camera will give far better color accuracy. Imaging
scientists describe the two different responses as 'densitometric' (cmy) and
'colorimetric' (rgb).
Some pigments are known problem colors for (particularly digital)
reproduction. I would be very interested in hearing about list members
experiences of problems with getting accurate color.
Thanks
Tony Riley (Kendal, UK)
email@hidden
www.tonyriley.dsl.pipex.com
Hi Tony,
I agree with you. Although most scanback cameras use IR filters in
order to cut off the spectrum of the light that they are more
sensitive to than the human eye it is still very difficult to match
certain colors (pigments) with scanback technology. It seems that the
problem is the lack of a perfect match between CCD sensitivity, IR
filters and lights spectral quality.
In a simple test we could show that allmost all scanbacks we tested
do not quite match human visual perception. Kodak has an interesting
target ("Kodak Color Viewing Light Selector, P3-180, CAT No. 845
6022) that perfectly shows metamerism. While the most expensive and
sophisticated scanback solutions show metamerism with this target, a
simple Nikon Coolpix 5000 does not show any under the same 5000K
lightsources. This does not proof much but confirms your theory.
I think it would require better filters and/or coated CCDs as well as
lightsources with optimised spectra in order to achive more accurate
results digital art reproduction. Too often bad results are blamed to
bad color management software or targets. I assume that targets could
be improved and that watercolor-, oil-, acrylic -targets etc. could
be developed.
Are you familiar with the IBM PRO\3000 - multi-spectral image
acquisition and spectral reconstruction using a trichromatic digital
camera system associated with
absorptionfilters.(
http://www.cis.rit.edu/research/mcsl/research/CameraReports.shtml
)
Also check out Robin D. Myers PDF on Color Accurate Photography of
Artworks (
http://www.rmimaging.com/information/information_index.html)
Stefan
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