RE: RGB vs CMYK: gamut and some important notes for CMYK users

"Keith, you cite "specification of the *ink*" above, which
sounded to me like you meant the ink of the printer for a digital print,
rather than the paint chosen for a gum print. Is that correct? In which
case, would the other parameters apply?"

Judy - No, I was not referring to paint OR to ink of a digital print, but
rather to a specific required inkset parameter selection in the Photoshop
color space setup. I said "This data is changed intentionally during the
CMYK conversion, and it is changed in order that the closest colors possible
to the original photograph are in the output. Taking into account the
parameters specified in the CMYK setup, and the specifications of the ink
that is chosen, the CMYK channels look different. Those inksets in CMYK are
important"

We gum printers have not amassed significant attention at Adobe for them to
consider our pigment need on their CMYK calibrations. So... we have to make
do with what they provide, which means we have to make a selection based
upon the limited number of CMYK separation calculations they have provided
for the printing industry. CMYK, being what it is - algorithms for
adjusting the separations in order to optimize usage of a limited number of
inksets - will only get us into a "make best" scenario. In order to use any
of the Photoshop CMYK color settings, an "ink color" has to be selected in
the "ink options" portion of the CMYK color settings working spaces. So
while "ink" is not a term that has much relevance for OUR purposes, we have
to go with the flow. If you were to go (in PS 7) into edit/color
settings/working spaces CMYK, you will find a limited number of ink options.
With a little trial and error, one can find a combination the suits ones
purposes. Here is an interesting test: first make a duplication of your
full-color RGB image. For one copy, change the CMYK inset to "Japan Color
2001 Coated". Convert mode to CMYK. For the other image, repeat the
process using "US Web Uncoated v2", Convert to CMYK and toggle between your
two images. Both CMYK, but pretty different, right? An experienced gum
printer ought to be able to see how those two sets of separations might
provide for different results when applied to gum printing.

I hope this makes sense. It's the best I can do at midnight.

Keith
-----Original Message-----
From: Judy Seigel [mailto:jseigel@panix.com]
Sent: Saturday, December 04, 2004 8:55 PM
To: alt-photo-process-l@sask.usask.ca
Subject: RE: RGB vs CMYK: gamut and some important notes for CMYK users

On Sat, 4 Dec 2004, Keith Gerling wrote:
> ... Taking into account the parameters specified in the CMYK setup,
and
> the specifications of the ink that is chosen, the CMYK channels look
> different. Those inksets in CMYK are important.

Since most of my own gum printing (except for a brief interlude a while
back) has been in fake color from monochrome, I'm happily enjoying this
discussion as innocent bystander. However I do have one question and one
comment:

Question: Keith, you cite "specification of the *ink*" above, which
sounded to me like you meant the ink of the printer for a digital print,
rather than the paint chosen for a gum print. Is that correct? In which
case, would the other parameters apply?

Comment: Anyone who unsubscribed from this list because of dissent, even
argument, about CMYK vs RGB, has really really really got to be too
sensitive for this world. Meanwhile, however, I don't recall any such
to-do, and I've been here all along.

love & kisses,

Judy
Received on Sun Dec 5 00:02:28 2004