Re: CMYKOG profiles in PosterPrint RIP?
Re: CMYKOG profiles in PosterPrint RIP?
- Subject: Re: CMYKOG profiles in PosterPrint RIP?
- From: Graeme Gill <email@hidden>
- Date: Mon, 05 Jan 2004 21:24:35 +1100
Robert L Krawitz wrote:
I'm thinking about how to handle this in Gimp-Print. The option that
seems most obvious to me is to offer a choice between conventional
4-color and CMYKRB, and if the user selects CMYKRB, to perform an
operation analogous to GCR to generate red and blue if there's a large
component of blue (C+M) or red (M+Y) left over, after subtracting out
virtual (CMY) black (real black is removed from CMY in the GCR
process).
This sort of approach generally works really badly. You won't get
anything like the available gamut. This applies to substituting
black for CMY, as well as substituting Green/Orange etc. for pairs
of CMY. Substitution of K for CMY results in a characteristic
gamut consisting of the CMY gamut plus a narrow K cone sticking out
of it. The article "Black generation using lightness scaling" by
Tomasz J. Cholewo illustrates this well (google).
On a CMYKOG printer I looked at, the gamut for the O & G was
actually less than that available just using CMY. An expansion of the gamut
was only evident when the O or G was combined with C, M and/or Y.
GCR type approaches in device space seem to be just a poor fit to
actual device behavior.
Graeme Gill.
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