Re: Uniform Perceptual Lab space v2
Re: Uniform Perceptual Lab space v2
- Subject: Re: Uniform Perceptual Lab space v2
- From: Tim Vitale <email@hidden>
- Date: Thu, 26 Feb 2004 12:24:34 -0800
I discovered an adaptation of CIE Lab color space some time ago on Bruce
Lindbloom's website. The discussion on its use describes the problems
that I have been having with printer output. Saturated blues go purple,
saturated reds go orange and images with little more than shades of
yellow are under saturated.
I'd be interested to learn more about your experience with this phenomenon?
Care to elaborate some more, quote some figures?
Just go to www.brucelindbloom.com, navigate to the >Info>, second item
on the right >Uniform Perceptual Lab Profile> in the text click on the
link "blue turns purple." This tells the whole story. The problem I
had was this was not showing up on screen because it was in the gamut
remap the profile makes prior to printing. Do the exercise he
recommends with reds. In the >Calc> page, select the >Munsell Display
Calcularor> and follow his direction in "blue turns purple" discussion.
The problem with the yellows shows up as an egg shaped chrome rings.
Because the circle is stretched to an egg shape, extra yellow (and
yellow-greens, but not my issue) needs to be added to most of my images
of old paper artworks. This is found by setting the calculator to
Model: Lab; Hue: 2.5 YR; Value: all; Chroma: 4-20. The egg shape tells
it all.
I've read the articles recommended and have ordered the
"Postscriptum..." book. Now I'm wondering which developers are using
CIECAM02?
Is CIECAM02 going to be in the new release of ProfileMaker, v5?
I use PM 4.1.5 (and Bill Atkinson) profiles on my Epson 9600 & 10000. I
think the excellent Atkinson profiles were ultimately created using the
same Gretag engine. As good as Gretag is, the profiles still have the
problems I've noted due to the Lab PCS. Non-linerarity appears to be
the problem, even though many trained observers don't see the problem in
most test images. When you are doing a reproduction of a "Mao red"
calligraphy banner and the printed red is red-orange you know you have
the problem. When you start with a "cobalt" blue watercolor of 41, 50,
-85, you finish with a 41, 65, -70, purple.
The good news is that now that I know the problem, I can stop suspecting
links in my "chain of tools" and stop conducting a futile search for a
problem within them. They may still exist, but the CIELab problem is
far worse for my projects.
Thanks to all
Tim Vitale
Conservator
510-594-8277
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