Re: Digital Negs - RGB vs CMYK

From: Katharine Thayer ^lt;[email protected]>
Date: 12/02/04-01:09:44 PM Z
Message-id: <>

Christina Z. Anderson wrote:
> Whoops, I did not make my post clear; I have no problem or question with the
> not using the K layer. That makes sense. My question is this:
> with CMYK does the C print cyan, the M print magenta, and the Y print
> yellow, as Livick says, or does the C print red, the M print green, the Y
> print blue??? And if C prints C and M M and Y Y, why is that not the case
> with RGB, too? Mind you, I've never done CMYK seps or felt the need to,
> having come to gum before digineg seps were possible and the option was
> color seps in the darkroom with RGB filters...

You were making tricolor gum prints before imagesetters? Before laser
printers? There were people making tricolor gum prints from digital
separations for a long time before inkjet printers got to where they
could do a reasonable job on digital negatives. But I must say that if
you made your early color separations in the darkroom with filters, I am
very impressed. I know Dave's done this, and I think Sam has done it,
but I've never done it myself.

I've been thinking about this whole question of why some people prefer
CMYK and others prefer RGB, and it seems to me that perhaps you could
make a case for the proposition that people who came to color gum
printing from color photography think in terms of color photography
when approaching gum printing, and the RGB route makes more sense to us.
But for people coming from printmaking, or from commercial printing or
pre-press, then the CMYK route may seem more logical. Just a thought....

But to your question: With CMYK the separations print the color layer of
their own name. With RGB, Photoshop isn't smart enough to change the
name of the channels to Cyan, Magenta and Yellow when the RGB file is
inverted to CMY, so you have to do that in your own mind, reminding
yourself that Red is now Cyan, Green is now Magenta, Blue is now
Yellow, unless you use the easy Multichannel route I described last
week, in which case the channels are actually named Cyan, Magenta and
Yellow. (However this is true even if you don't invert the file. They
are spot channels, which is another commercial-printing thing.)

One thing that might be confusing is that when you invert the RGB image,
what you're looking at onscreen is the negative of the CMY image,
whereas when you're looking at the CMYK image onscreen, you're looking
at the positive, and you either have to invert again or check "Print
Negative" in Page Setup to get the separations as negatives.

Received on Thu Dec 2 21:05:54 2004

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