Re: ProfileMaker yellows turn green
Re: ProfileMaker yellows turn green
- Subject: Re: ProfileMaker yellows turn green
- From: David Wollmann <email@hidden>
- Date: Mon, 10 May 2004 14:20:52 -0600
From: Graeme Gill <email@hidden>
1) Use of a colorspace such as L*a*b* for gamut mapping/clipping,
which is
known to have a mismatch between lines of constant a*/b* ratio and
human
perceived constant hue. This is especially obvious in the blue
region,
but may have an effect elsewhere as well, such as the red or
yellow.
2) Gamut mapping being done with a simple constant hue angle type of
algorithm.
The yellow "cusps" of most devices in a perceptual colorspace are
generally
very sharp and narrow, so any gamut mapping algorithms that
operates on the
basis of keeping the source hue angle constant, and particularly
if it has a simple
geometric approach to altering saturation, has little chance of
intersecting
the destination yellow cusp at its tip (ie., where it is pure
yellow in the
output device). A gamut mapping/clipping algorithm that has some
weighting
towards the nearest point on the destination gamut is necessary to
address
this problem.
3) The gamut mapping/clipping space not allowing for the
Helmholtz-Kohlraush
effect, which models the effect whereby highly saturated colors
appear
lighter than less saturated colors.
4) Standard ICC workflows are based on the "smart profile, dumb
linker" model,
where things like gamut mapping are encoded at profile creation
time, and
stored in the B2A tables of the destination profile. Since the
destination
profile is usually created without any knowledge of the source
gamut, most
packages (I assume) are forced to use a generic gamut mapping.
This means
that even if points 1), 2) & 3) above were taken into
consideration, there
is practically no chance that yellow will be mapped the way you
would like,
since the destination profile has no knowledge of the source
yellow it is
meant to be mapping from.
Hi,
I am using Onyx Production House 6.0 (Postershop) and I believe the
profiling part of this software uses ProfileMaker, or parts of it.
Occasionally I have problems with the same thing, my bright yellows
look greenish having a small amount of cyan dot showing up. One of the
options I have is selecting yellow as a pure hue. This will take care
of Pure Hues but what about other yellows that are very close to pure?
Is this setting absolute in choosing a Pure Hue, or is there some built
in range setting that will allow a lesser effect on hues that are close
to pure and print them with proportional less cyan? I'm thinking
probably not.
And if not would these other shades that are close to pure need to be
corrected through profile editing or a device link?
Thanks,
David Wollmann
Luna Vista Imaging
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