Re: Lab values for cmyk colours exceeding the total ink limit
Re: Lab values for cmyk colours exceeding the total ink limit
- Subject: Re: Lab values for cmyk colours exceeding the total ink limit
- From: Graeme Gill <email@hidden>
- Date: Mon, 01 May 2006 10:13:26 +1000
Giordano Galli wrote:
Are the relevant data included in AToBxTag tags? IOW, are LUT-based
profiles required or allowed to implement a complete Device to PCS
mapping? If so, I can't think of how this could be achieved in some
situations, eg when mapping [90 70 70 100] for a newsprint profile,
as this would involve printing 'forbidden' patches.
There's no "requirement" to have a completely accurate Device to
PCS mapping in the A2B tag, but the tag stores values for
a complete mapping. Outside areas actually measured
in making the profile, the A2B tag is going to be filled with
values of one sort or another, and the profiling software will
have to extrapolate (ie. guess) values. These values generally
can't be relied upon.
A weakness of the current ICC format is that it doesn't
have a clear way of indicating what the ink limit is,
and hence where the accurate A2B region ends. Generally
the user will have to keep track of this manually.
Graeme Gill.
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