RE: Digital Negs - RGB vs CMYK

Oh Michael, your printer may be using CMYK inks to print the image, but
this doesn't mean that it will print CMYK separations........(shakes
head a little)...the printer inkset has absolutely nothing to do with
making separations.

When printing gum, you use the R negative to print with a cyan pigment,
the G negative to print magenta, and the Y negative to print with blue
pigment. So the IMAGE is CMY (unless you want to alter the pigments of
course). The main debate between RGB and CMYK is that a lot of the
density with CMYK is carried on the K channel, therefore (some say, and
I would tend to agree), you must print with a K pigment to get good
density, and this interferes wiyth the other pigments in some areas of
the print. With RGB negs, the density is carried in the colour chanels,
and the shadows are built up of colour overlays. Here, if you don't get
your pigments right, and you're going for accurate colour, you can get
strange colour shifts in the shadows.

Here endeth the lesson.

My 2 cents' worth: I've tried both CMYK and RGB for gum printing over a
period of time - in fact I was told at the start that I could just print
with CMY and forget about the K separation - this I've never done with
any success.....I have reverted to RGB, and like this just fine -
sometimes I've printed a skeletal K just to bump up the density, but I'm
not that happy about this either..... I'm about to start reviewing my
negative production and being a lot more critical about it.

Anyhow, what seems to happen is that people get one system and learn to
use it, then stick with it. I'm all for that - stick to what suits you
and do it well.

Kate
 

-----Original Message-----
From: Michael Healy [mailto:emjayhealy@earthlink.net]
Sent: Wednesday, 1 December 2004 8:54 p.m.
To: alt-photo-process-l@sask.usask.ca
Subject: Digital Negs - RGB vs CMYK

Now that the smoke has cleared a bit, I'm going to be rash and stick my
neck waaaaay
out there with a few little quasi-neophyte questions. I want to be clear
about something,
though: I am not interested in getting up people's dander, or getting
myself tangled up in
the age-old argument over which color mode is sacred. I'm interested in
understanding -
for home printers - why there is a differences between these modes to
begin with.

Now, I understand the requirements of a printing house: CMYK since
Gutenberg. My
problem, though, is that I happen to print my negs on an Epson inkjet
printer that's
sitting here at my elbow. Okay, so one way I can print my negs - or my
separation negs -
is to leave them as RGB; then again, I can take the trouble to convert
them to CMYK
before I print them. I gather that some people grow hives at the thought
of one, while
others are growing second and third heads at the thought of the other.
The whole thing
gets me totally hung up, though. Here's why: the last time I looked, my
Epson was using
CMYK inks. To my uninitiated eye, it doesn't seem to matter what I do
with my file - the
thing is going to get ripped as a CMYK file, period.

So what is it that I am missing? I can convert a neg (or its separation
components) to
CMYK, and then won't it print as CMYK, unaltered? Or I can be lazy and
leave it as
RGB. Then the printer intercepts it, and converts it to CMYK anyhow, and
then prints it
as CMYK.

So I am wondering about three things:

(1) what difference does any of this make, if the thing has to end up
CMYK anyhow?
Why does it matter what your Photoshop mode is (assuming it is color,
not b&w)?

(2) If it is true that both RGB and CMY get turned into CMY by my inkjet
printer, then In
terms of inkjet printing (NOT print shop printing!), what exactly is it
that CMYK
advocates are advocating, that I should take this extra step to convert
it? And what is it
that the RGB advocates are missing, that they think they actually are
pulling off an RGB
print through a CMYK printer?!

(3) GUM! If an inkjet printer does print CMYK, why do people use
painter's (RGB)
colors? It would seem to **require** that one use printer's (CMY) colors
- assuming, at
any rate, that one wants "realistic" colors. How come RGB pigments used
on inkjet negs
don't turn a gum print into something resembling cross-processed C41?

Mike

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