Re: Custom ICC Profiles/Conversion Rending Intents
Re: Custom ICC Profiles/Conversion Rending Intents
- Subject: Re: Custom ICC Profiles/Conversion Rending Intents
- From: Chris Murphy <email@hidden>
- Date: Sun, 19 Jun 2005 09:36:35 -0600
On Jun 18, 2005, at 11:32 PM, Graeme Gill wrote:
It's a strange profiling package that would let the GCR have any
effect
on the ink limit.
Perhaps :) But it's not wrong for the UI to suggest, for a given data
set and GCR that there is no point in requesting a higher ink limit
because you aren't going to get any further increase in density, just
use more ink. In fact, it's entirely possible by using more ink,
you'd end up with a lower density.
Generally it is assumed that the ink limit is a much
higher priority than the GCR, so it should be adhered to under all
circumstances. GCR is a preference, adhered to if possible (at least
that's how my software works.)
They're absolutely related. So long as CMY alone won't produce as
dark and neutral a color as 100K, some black generation is necessary,
even at a 400% ink limit. But as ink limit decreases, by definition
black generation increases, and vice versa. Most packages consider it
a relative value leading one to believe the difference between a
light GCR and heavy GCR is the same for a 240% ink limit and 350% ink
limit. But that's not how it works. There really is no such thing as
light GCR for a 240% ink limit, if you're going to accept the status
of black generation as being a singular event. And for a heavy GCR,
and ink limit of 350% is probably never going to be reached (and if
it is reached, I wonder where the heavy black generation is!)
The ink limit should not be exceeded, but so long as the same black
point can be achieved with lower values, that's traditionally been
acceptable. The question is, do profiling packages adequately sample
enough black patches to do a stellar job of determining the black
point, or is this being interpolated and hence possible for it to be
wrong? My experience is when they produce an area of coverage less
than the ink limit, it's often not achieving the best possible black
point within the ink limit I've specified.
And if a light GCR isn't possible for a given data set, and ink
limit, I argue the UI shouldn't let me choose it. I agree that ink
limit should not be busted.
Technically it's possible to find output of a B2A table that exceeds
the ink limit, due to the nature of the interpolation. Just because
all the nodes of the multidimensional grid are at or under the ink
limit, doesn't ensure that the interpolated device values between the
nodes of a cell are going to be under the ink limit.
Wow, that's pretty silly. Maybe CMYK output device profiles need a
required black point tag, including both a device independent and
dependent value, so that the CMM can ensure the ink limit isn't busted.
Chris Murphy
Color Remedies (TM)
www.colorremedies.com/realworldcolor
-------------------------------------------------------------
Co-author "Real World Color Management, 2nd Edition"
Published by PeachPit Press (ISBN 0-321-26722-2)
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