Perceptual Javex
Perceptual Javex
- Subject: Perceptual Javex
- From: "eugene appert" <email@hidden>
- Date: Thu, 21 Sep 2006 11:39:11 -0400
Hello ,
I have a limited understanding of the inner workings of icc profiles. I am
noticing an anomaly with the perceptual rendering of a specific scanner
transparency profile written by Monaco Proof. Using perceptual rendering
for the conversion to any RGB work space it bleaches out values lighter
than L*88. RGB source 212, = L*88 converts to RGB target 255 = L*100.
Monaco Proof does not appear to offer any opportunity to modify the table
used for perceptual rendering, definitions of white and black points or the
reproduction curve.
The reference tables indicate that the value of the GS0 patch should be
L*88, so the profile appears to be accurate. The Scanner in question
produces RGB 212 at that patch. After the conversion to any RGB workspace
using perceptual, all RGB data above 212 is written to 255= L*100 A
reflective profile for the same scanner made with the same software does not
share this problem. In that case the GS0 produces RGB 214 which the profile
links to L*85 and after conversion (to an RGB workspace) using perceptual is
written to L*90. Strangely, Colorthink shows both of these profiles extend
to both extremes of the L* axis.
Obviously perceptive rendering would never be used for this conversion, its
just something I cant explain and am curious about.
Thanks for any light you can shed on this
Eugene Appert
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