RE: CMYK separations on Adobe Photoshop

>>> Keith@gumphoto.com 11/05/04 2:11 AM >>>
... 5) the information contained in these channels is black and white.

I don't understand the concern over orthocromatic lith film, because in
no
case will anything other that white light be projected onto it. I ask
you
to explain in more detail why "red response" in the copy negatives would
be
a factor. I'm not well acquainted with using inkjet negs, but again, I
fail
to see how the spectral inks in an Epson 2200 could play a factor once
the
color component has been neutralized via the separation process.<<<

Keith,

I guess I don't understand your reference to using orthochromatic film
at all. Why is there a need to involve it in the process? Are you
possibly thinking about outputting the separated grayscale channel info
onto an inkjet or imagesetter transparency as a positive and then
enlarging that optically onto a lith film? (I tried enlarging an inkjet
transparency once and it look terrible on the copy film.)

Since the ortho film is insensitive to red, you can't take a color
transparency (or negative) and enlarge it directly onto the lith film
without losing the red information. The red would be grossly
underexposed relative to the other colors. You would need to print the
original film onto a panchromatic film first using separation filters in
the optical enlarging system and then take the resultant grayscale
negatives/positives and dupe them onto the ortho emulsion. I suppose if
you have a film recorder hooked into a digital system you could output
onto film using Photoshop to do the separations and then copy those
negatives onto lith film, but I'm not sure if that is what you are
referring to.

The neat thing about using the digital inkjet negatives is that they
come out of the desktop printer ready to use in contacting printing the
emulsion.

>>>... For one thing, my process
renders it impossible to expose the CMYK and RGB components
simultaneously
for the mere reason that this would require the negatives to be
perfectly
equal in density. There's no way I could accomplish that using two
pieces
of lith film developed separately.<<<

This problem is avoided using the digital route.

As far as your question regarding the inkjet printer inks affecting the
spectral response, I'd direct you to Dan Burkholder's digital negative
book or perhaps Mark Nelson's new book on Precision Digital Negatives
(although I have not seen the latter). Dan describes the making of a
spectral inkjet negative that is orange in color and though thin in
density optically, it is deceivingly effective in blocking UV upon which
most of the alternative processes use. The more orange ink, the more
pronounced is the spectral effect. From recent discussions on this list,
I assume Mark's process may use an optimized spectral negative as well.
 Pyro developed conventional negatives also rely on the greenish stain
to attenuate UV. Another instance of a UV blocker is the new TMAX 100
film base which makes the new film a poorer choice in printing several
alternative processes.

My speculation about the inkset perhaps blocking certain wavelengths is
related to these examples. I simply don't know if the negatives printed
with color inks as opposed to black ink block the UV radiation any
differently and thus distort the color response even though both
negatives appear neutral. My guess is that this is not a real concern
based on the negatives I've made so far. It's just total speculation on
my part. Sorry if it confused the issue.

Joe
Received on Fri Nov 5 07:45:04 2004