Re: Rendering Intents
Re: Rendering Intents
- Subject: Re: Rendering Intents
- From: Chris Murphy <email@hidden>
- Date: Tue, 3 Sep 2002 09:49:17 -0600
On Tuesday, September 3, 2002, at 08:53 AM, bruce fraser
<email@hidden> writes:
I've never seen Postscript color management work in any practical
way. You can only load one CRD per job, so you get a
one-size-fits-all rendering on the output side. (And that's if we
even had tools for loading CRDs!)
It does work for proofing where the file being sent contains normalized
objects, such that all PostScript Color Management needs to do is make
one device simulate another.
As for one CRD per job, this isn't a PostScript color management
limitation but an application limitation. In the case of InDesign 2 it
will download CRD's for every rendering intent specified in the
document. If you have just one rendering intent specified, there will
be only one CRD in the PostScript stream. If you are using four
rendering intents, there will be four CRD's in the stream.
All of the Adobe applications are capable of placing a CRD in a print
stream, but only InDesign 2 and Acrobat 5 will produce a CRD for each
rendering intent specified because only those two applications would
have documents containing multiple objects that could have different
sources as well as different rendering intents specified. Illustrator
and Photoshop documents have one profile that applies to the entire
document, so they only need to generate one CRD if you print from those
applications.
If you use perceptual renderings in and out of the PCS, all bets are
off unless you've been very careful to build matched sets of
profiles. But relcol renderings generally give predictable results
between different profiling packages and different CMMs. Relcol in
and Perceptual out usually doesn't create too many headaches either.
But given the composition of the ICC, it's somewhat amazing that they
managed to reach the degree of consensus that they have...
All Adobe ACE conversions use the same table in and out. So if you
specify perceptual, you will get perceptual rendering to the PCS and
from the PCS: AtoB0 used in source, and BtoA0 used in destination. If
you specify saturation, then the saturation intent is used in both
profiles.
However, it's not uncommon for profiles to have AtoB0, AtoB1 and AtoB2
all point to the same data - effectively relative colorimetric, so that
conversions to the PCS are RelCol. It's also not uncommon for profiles
to have AtoB0 and AtoB2 (perceptual and saturation rendering) point to
the same data, while AtoB1 (RelCol) has it's own data.
I'm not sure how the Apple CMM or Heidelberg CMM work in this regard.
The CMM could certainly choose to always use AtoB1 (if it exists) in
the source profile, but this is not how ACE works at least.
Chris Murphy
Color Remedies (tm)
Boulder, CO
303-415-9932
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