Re: GCR and UCR

From: Katharine Thayer ^lt;[email protected]>
Date: 09/14/04-03:54:34 AM Z
Message-id: <>

Keith Gerling wrote:
> seems like a lot of reminding...
> In the first place, I have no idea what those acronyms refer to, nor does it
> matter. Secondly, I don't know what the default is, but I thought it was
> UCR, not GCR. I don't pretend to be an expert on this. People on this list
> tend to refer to CMYK as if it were some static definition of color - as if
> it were the opposite of RGB. That isn't the case.

Hi Keith,

I agree with you, of course; my point in reminding folks that the
default is GCR (Photoshop manual: "By default, Photoshop uses the GCR
type of color separation") was to emphasize the point you are making
above, that if people think that they get a straight conversion of RGB
to CMY when they click "CMYK" on the Mode menu, they are seriously
mistaken, especially since the default CMYK space uses GCR, which alters
the color information even more than UCR, although both of them alter
the color information more than I would ever want my color information

You are right, of course, one can play around with the settings and get
CMYK spaces more to one's liking, as you have done most ably, but many
people don't know anything about that, they just click CMYK and "print
separations" (and a pox on teachers who tell students to do this) and
think that the RGB converts in a straightforward way to CMY and then
adds a black printer in addition to the straightforward CMY.. This of
course is not at all true.

I've never been able to understand why gum printers attempting to print
color are forever telling me that you can't get a decent color print
using a tricolor method, and that it's necessary to use black as well.
This of course isn't true, as I've demonstrated and Livick has
demonstrated and any number of expert tricolor gum printers have
demonstrated for years.

BUT (and this is important) if you get your three color printers and
your black through CMYK separations, then of COURSE you have to use the
black printer, because that's how the separations are designed. Density
(I'm thinking print density here not negative density) is stripped out
of the color layers and shifted to the black layer, so of course
printing just the three colors is going to give you a wimpy unsatisfying
color print and you're going to need to use the black printer, where
much of the print density has been deposited. But the point is, if you
had stayed with the RGB file and kept the straight color information,
none of this would be necessary.

According to the photoshop manual, here's the difference between GCR and

"With UCR, black ink is used to replace cyan, magenta and yellow ink in
neutral areas only....With GCR, black ink is used to replace portions of
cyan, magenta, and yellow ink in colored areas as well as neutral
areas." Either way, you HAVE to print black (or some color using the
black printer) to get the density you expect in the neutral and shadow
areas. I guess I don't see the point of taking color out and replacing
the color density with black, when color by itself, left alone, works
just fine. The CMYK spaces are necessary for the printing industry, for
their machines and their inks and their papers, but they have little or
nothing to do with gum printing, in my opinion.

Katharine Thayer
Received on Tue Sep 14 10:50:46 2004

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