Re: Media Testing for maclife.de
Re: Media Testing for maclife.de
- Subject: Re: Media Testing for maclife.de
- From: Klaus Karcher <email@hidden>
- Date: Mon, 08 Sep 2008 11:47:10 +0200
Robin Myers wrote:
[...] what is needed is not a single approach (i.e.
ICC) but more new thinking on the matter. Adobe has done some work and
developed the color model embedded in DNG and presented in it's Camera
Raw product. I give them kudos for attempting something new. What other
companies are developing new approaches?
I have developed an successfully implemented a two-stage process for
artwork reproduction. The primary target area of application is a repro
system with a three-line Scan Camera and adjustable light sources, but
further tests suggest that it's also applicable to mobile setups and
cameras with full frame sensors.
Stage one is the careful and extensive profiling of the system with
various targets (I use Aryll to create the profiles). It has to be
carried out only once for each class of artworks.
Stage two is a simple calibration and linearization procedure for
/every/ scan based on a small gray wedge. It only takes some seconds per
scan.
I managed to turn a system that needed a separate profile for every
lighting condition and still produced unstable results with average
Delta E's of 12 into a system that only needs one profile to achieves
stable and reproducible results under all light setups with average
Delta Es of 1.9 (for arbitrary masters) and 1.1 (when the pigments of
the target and master are reasonably concerted). All numbers refer to a
test set that contains patches strongly susceptible to metamerism failures.
Some of the quality limiting factors are fairly constant (e.g.
metamerism failures in consequence of sensor or lighting properties) and
others (like variations of the light sources, exposure and temperature
dependend sensor noise or incomplete bias compensation) vary from scan
to scan (or shot to shot). The former factors are correctable by the
profile while the latter can be balanced by the individual
calibration/linearization procedure.
Klaus Karcher
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