Re: U.S. Sheetfed vs. U.S. SWOP
Re: U.S. Sheetfed vs. U.S. SWOP
- Subject: Re: U.S. Sheetfed vs. U.S. SWOP
- From: Graeme Gill <email@hidden>
- Date: Thu, 03 May 2007 13:25:23 +1000
Steve Upton wrote:
4. Absolute Colorimetric - CSU( not available ), CTPro(default) - you are seeing the gamut of the
device as described by the profile. The white point is lowered to actual paper white and the
black point raised to ink black..
When you say "raised to ink black..", this worries me. ICC relative colorimetric
only shifts the devices absolute black point very slightly as a side effect
of the white point shift when it is encoded into the table. The relative
colorimetric intent tables should not have had the black point changed
in any other way, unlike the perceptual table, which should have had its
black point expanded to that of the reference medium black (0.30911% reflectance).
The use of the perceptual intent for the default graph in the CSU is not a good idea - it
probably grabs the default intent recorded in the profile's header, but I'm not sure. The gamut
shown (without explanation) is again, NOT for the device and NOT the gamut produced when
printing. Strictly speaking, it is the gamut that you'll receive from the profile when using it
to convert a CMYK file to Lab (and on to another profile) using the perceptual intent; something
that is rarely performed in a workflow. Even in CMYK to CMYK conversions, rel col with BPC is
recommended...
The gamut portrayed by the non-colorimetric A2B tables can vary quite widely. On some
V2 profiles it may be identical to the colormetric table. On others, it will represent
vendors "secret sauce", and on ICC V4 profiles it is meant to be a transformation
from the device gamut to the Reference Medium Color Gamut, and hence should
look pretty the same as the Reference Medium Color Gamut :- so in my book, noone
should be looking at anything other than the absolute or relative A2B table
when it comes to examining the gamut of the device. The contents of
all the other tables only give an indication of how the profile creation software
is manipulating the color.
Graeme Gill.
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