Re: Digital Negs - RGB vs CMYK

From: Jim Morris ^lt;>
Date: 12/04/04-07:34:59 PM Z
Message-id: <>

This is most likely caused by making CMYK separations based on SWOP
inks. Equal amounts of C+M+Y theoretically should equal neutral, but
this is not the case with SWOP inks. Because of certain impurities in
the ink colors C+M+Y equals a reddish, muddy looking color. To make up
for this, the C+Y+M combination requires more C to neutralize the red
cast, and K to achieve a true black. If you look at the custom CMYK
set-up window in Photoshop 7 you will see a little graph with curves
showing how the colors are weighted for the separations. So, if you
are using CMY pigments, say for gum printing, that actually produces
neutral gray in equal amounts, then separations that are made based on
SWOP inks will most certainly produce a cyan cast when printed with the
gum pigments.

Photoshop will do almost anything you ask it to do but it gives you a
lot of options, the trick is to know what to ask. If you ask for
separations based on SWOP inks, that's what you get. CMYK offers a lot
of flexibility, and no, I'm not saying that it's better or worse than
RGB. What I am saying is that CMYK has to be applied correctly in
order to work the way you want it to and this makes it, seemingly, more
complex. The notion of creating CMYK separations by default in
Photoshop, throwing away the K, and printing in CMY, is almost as bad
as making RGB separations and throwing away the B.
I know that the default approach to CMYK is often recommended by people
who should know better; it's just plain wrong.

Jim Morris

Joe Smigiel wrote:

>> I certainly think you can get realistic/believable color
>> with either RGB or CMYK separations, but accuracy is another matter.
>> Most realistic-color gum images I've seen (primarily on the web) I
>> would
>> not call accurate. Many tend to have a cyan/blue bias IMO.
Received on Sat Dec 4 19:36:07 2004

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