I need some clearing up ...
I need some clearing up ...
- Subject: I need some clearing up ...
- From: "Daniel Lowicki" <email@hidden>
- Date: Sun, 22 Sep 2002 14:07:48 +0200
Hi all,
I generally have a firm grasp on colormanagement but there
come times when I try to dig into things even further
and don't really make any process because something
seems to be blocking my head.
I'd appreciate any comments about theese assumptions and
questions that bring more light into these issues.
a) When the relcol table is written the whitepoint scaled
to 100,0,0 but the blackpoint is not scaled so it remains
absolute colorimetric ? Or is there a blackpoint tag that
is thorougly supported and the relcol table is also blackpoint
relative ?
b) When I do a perceptual profile conversion from scanner to printer
and I look at it as a two step conversion scanner->Lab
and Lab->printer there should be absolutely no compression
in step one and the values should be passed to Lab in absolute
colorimetry (no matter which intent is selected).
Then the second step should do the perceptual compression.
After all the Lab space should be able to hold all the scanner values.
True?
c) The compression is hard coded into the profile tables. So in theory
the pcs to device table of a printer profile (say perceptual) has
to have an entry for each Lab value that could occur and define target
values for the whole Lab space. This would mean that even if the source
only covers a small portion of the Lab space and is still bigger than
the target space the compression would be huge. True ?
Question: Is there a weighting in the icc math that controls the compression
by how much of the Lab gamut a source space uses ?
Question: To my understanding a perceptual conversion is only useful if
the image uses portions of Lab outside the target gamut and if visible clipping
occurs. Is there some math involved that checks for overlaps and passes the
conversion through the colorimetric tables rather than through the perceptual
one if there are no overlaps?
I hope these questions don't seem weired but I have come across these questions
and found I am not able to answer them without blushing.
-Daniel
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