Re: Black generation questions for large format inkjet
Re: Black generation questions for large format inkjet
- Subject: Re: Black generation questions for large format inkjet
- From: "email@hidden" <email@hidden>
- Date: Fri, 20 Apr 2007 16:09:57 -0500
Using UCR instead of GCR solved this problem for me.
Hmmm ... glad to hear that using UCR solved a problem for you.
However, in
my view, employing this setting may create more problems than it
solves.
Admittedly I've never used it in a real printing system as you
have, but
I've had occasion to examine profiles internally, so my concerns
stem from
best practices of profile construction. As implemented, UCR forces
a very
long black start on neutral of about 50% to 60% cyan. This delayed
onset
creates a very steep rise in the 3/4 tones & shadows, a tonal
region where
ink gradients should be lessening not increasing.
Which is where I need it. My proofer doesn't have light black and has
pretty large droplets, so the idea is to use the black in areas where
it doesn't look like pepper.
Another negative
consequence of this rapid rise in K, is the colorimetric reversal
of the
CMY inks in the shadows. Monotonic behavior of all inks on neutral
is a
cardinal rule and the forced reversal of the chromatic CMY inks
violates
it. Additionally, this delayed and rapid rise of K also causes steep
off-axis gradients of all the inks as the gamut boundary is
approached.
I'm sorry, Harold. I don't know what you mean when you say
"colorimetric reversal" or "Monotonic behavior of all inks on
neutral" or "forced reversal of the chromatic inks". Could you
clarify, please?
In my view the UCR setting is an unnecessary vestige of a time when
separations were generated using films and wet chemistry. It was
defined
to work in the darker tonal regions of neutral inkings where a
given amount
of black replaced CMY. Rigorously speaking, this is in fact what is
happening in PM UCR profiles when the CMY inks reverse - you have K
replacing CMY. But this is a case of be careful what you wish for
because
it may come true. As I've pointed out above this is not a desireable
effect - it violates the overall principle that separations should be
smooth and continuous with decreasing ink gradients in the shadows and
monotonic behavior of all inks on the neutral axis.
I'm not using this profile to create seps - this is only for
proofing. Since this is on an inkjet I don't need any of the benefits
offered by GCR. I don't need stability at production speed, the black
ink doesn't prevent color inconstancy, the black ink doesn't provide
better neutrals than the CMYK mixes that result from the CMYK -> CMYK
transform at the proofer. The black provides beef and depth to the
images, and that mostly in the shadow end.
Are you saying that UCR makes the prints more susceptible to tone
reversals in the shadows? Guess I'll have to take a look at that.
Rich Apollo
G7 Certified Expert (and all around Good Guy)
314-344-1144
email@hidden
www.prioritylitho.com
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