From: Jeffrey D. Mathias (jeffrey.d.mathias@worldnet.att.net)
Date: 06/11/00-04:00:22 PM Z
Nick Makris wrote:
> ...
> What I am hearing you say is that the PT/PD chemistry responds differently
> to a digital negative than to an analog neg - perhaps not exactly, but that
> is my inference. Put another way, a digital neg that looks flat will
> produce the same results as an analog neg that looks contrasty - I have
> trouble with that.
The eye has a certain response to light, film has a certain response
which differs from the eye, and ink has another response different from
the others. And the flat digital negative you refer to may be intended
for an imagesetter. However I can assure you that a digital negative
printed form a HP DeskJet 970 definitely "looks" different than a Tri-x
negative both used to print the same image.
To test the transmission response of the ink do the following. Make
four gradients (and/or scan a 21-step) from 0% to 100% using only cyan,
magenta, yellow, and black. Print these with the DeskJet on
transparency film or cleared Tri-x film. Print these digital negatives
in Pt/Pd using an exposure that just gives maximum black to the uninked
substrate.
You should find that the cyan gradient prints all black as the cyan ink
will not block much if any UV. The magenta gradient will have enough
maximum density to print a medium gray. The yellow gradient will have
enough maximum density to print a lighter gray. Only the black gradient
will have enough density to produce a white if enough ink is coming from
the printer. You should also find that a Zone I is obtained quite a
distance up the gradient meaning the a bulk amount of ink is used to
just get to Zone one. Now if you use the yellow ink to provide a
threshold for Zone 0, the resulting black ink to provide the rest of the
zones does indeed "look" flatter than an analog Tri-x negative. Think
of the yellow as base plus fog.
What does this all mean? Not a thing. It only maters how the negative
prints with a given process, not how it looks on its own.
> And Jeffrey, I would very much like to see the curve you have eluded to for
> your HP inkjet.
Sorry I do not have a curve. I have determined that a single output
from photoshop will not produce enough different number of tones
especially in the highlight region. Therefore I have changed my
approach to build three negatives from photoshop. The first (base
layer) comprises the information in the original from Zone 0 to about
Zone VI. When printing this negative the printer has been calibrated to
only deliver enough ink when the maximum is called for to print as a
ZoneVI. The second (highlight mask) is comprised of densities that when
added to the base layer comprise about Zone VI to about Zone IX. When
printing this negative the printer has been calibrated to only deliver
enough ink that when the maximum is called for together with the maximum
from the base layer produces a Zone IX. The third (upper highlight
mask) is comprised of densities that when added to the other two layers
comprise about Zone IX to Zone XII or more.
Each one of these layers has its own curve. NOTE that the term layer
used here is NOT the photoshop layer but a finished digital negative.
The three layers (negatives) comprise the digital negative. As I am
still tinkering with this, you will have to wait until I publish this in
my guide. This is taking a back seat to some other projects, but will
eventually get done.
By the way, I have noted that after making a print, I will likely go
back and tweak the curves to produce a better set of negatives/masks.
Not really different from what I do when making analog negatives and
masks, but with more control.
-- Jeffrey D. Mathias http://home.att.net/~jeffrey.d.mathias/
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