Re: embedded vs untagged gamut plot
Re: embedded vs untagged gamut plot
- Subject: Re: embedded vs untagged gamut plot
- From: Terry Wyse <email@hidden>
- Date: Wed, 24 Nov 2004 17:59:05 -0500
I understand that you figured out what was going on but this got me
thinking about an example that Gretagmacbeth uses to show how their
profiling targets are "superior" (this is back in the days of the TC3.5
and TC6.02 charts) to a standard chart such as the IT8.7/3.
They will take a raw CMYK reference file (text file) from either of
these charts plus the IT8 reference data, open it in Logo ColorLab, and
then plot them on a 2D gamut viewer. What it will show is a nice even
distribution of values with their chart vs. the IT8 plus it reveals a
lot of wasted/duplicate patches in the IT8.
What I could never get (and I even asked!) was, how can you plot raw
CMYK values in a gamut viewer without SOME sort of assumption of what
the profile is? It just doesn't work. I suspect what MAYBE was going on
here was that it was using some sort of assumed CMYK profile, possibly
from Colorsync.
Terry
On Nov 24, 2004, at 3:24 PM, Mike Eddington wrote:
If you convert an image to the SWOP profile and save it twice, once
with
the profile embedded and once with no profile, you get two images with
identical CMYK values. However, when one uses a gamut viewer to view
the distribution of the images plotted onto the SWOP profile, the
untagged image has shadow values that fall well below the SWOP profile.
I would guess that this has to do with the fact that the gamut viewer
has to somehow infer Lab from the untagged CMYK as it has no profile to
rely on, but how would it do this...assume some other profile?
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