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
- Date: Thu, 19 Apr 2007 14:29:01 -0700
On 19-Apr-2007 14:43, Rich Apollo wrote:
>>.
>>.
>>I'm using a low CGR (CGR1), black start at 40% and I'm limiting the ink
>>(each channel) in the RIP.
>>
>>What's the best approach to deal with my scenario ?
>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. 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.
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.
Harold Boll
TOSHIBA AMERICA BUSINESS SOLUTIONS 2 Musick, Irvine, CA 92618
Harold Boll | Color Scientist | 1.781.856.5174 |
email@hidden
" The sunlights differ, but there is only one darkness. "
Ursula K. Leguin
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