From: Jeffrey D. Mathias (jeffrey.d.mathias@worldnet.att.net)
Date: 05/03/00-06:52:37 AM Z
I have been working to get a decent digital negative for Pt/Pd printing
from a HP ScanJet 6300C, a HP DeskJet 970Csee, and Adobe Photoshop V.
This equipment may do the job.
The black and yellow inks seem to be the only ones worth using for Pt/Pd
negatives. [Cyan is transparent and Magenta slightly responsive.] They
will provide plenty of density to give pure white in the print. An
amount of about 50% yellow is needed to provide the least amount of
density that will print black close to that of blank substrate. The
substrate I have chosen is either HP Inkjet rapid Dry Transparency film
or Kodak Tri-X film (fixed in Kodak Rapid fix part A only and washed).
It has been tricky to get the printer and Photoshop to only print yellow
and black ink, but I have found how to do that. It is tricky because
Photoshop and the printer each have there own minds (so to speak) and
try to redo the colors. I will report the details when finished with
this project.
The main problem is to get enough number of tones to give adequate
discrimination and quality in the print. I have been able to get about
300 separate tones. I do this by using the yellow ink from threshold
black (the density that gives black in the print closest to blank
substrate) through about zone two, then by using the black ink. The
yellow reaches a maximum density (but not maximum yellow) and is
supposed to remain constant, however Photoshop decides to reduce the
yellow as black increases after a certain level of black. This
reduction of yellow does not seem to interfere with a continuous
gradation of density, but I have concern as to if it will be
consistent. I would prefer to have the yellow present. Also note that
it has been tricky but necessary to keep each tone within gamut of the
printer (an out of gamut color may not be printed properly).
Because I am not using RGB values of zero, the black gives 255 tones.
The yellow provides an additional 45 tones where there is no black.
This provides the 300 separate tones. I am not sure at this point if
the 300 tones are enough to produce a Pt/Pd print indistinguishable from
a print made from the original negative.
The lack of number of tones can result in a reduction of subtle tonal
gradation or a reduction in the substance, depth, or quality of the
image. This may account for a lack of life in prints from digital
negatives reported by some people. And this can be more of a problem
for Pt/Pd prints than for prints from other processes (process with less
tonal discrimination such as gelatine silver). Perhaps the largest part
of the problem is that the tones are distributed non-linearly with fewer
tones describing the highlights of the image. Additionally if one is
not careful when converting modes in Photoshop, additional highlight
tones will be lost or merged (the densest ink portions). The highlight
values (and separation of highlight values) are so important to many
images.
Due to the ability of the Pt/Pd process to discriminate very subtle
differences in values, the limit of available tone values may be
critical in the ability to achieve a print with the quality of a print
from an analog negative. I find that some of my trials have such
problems. This tonal issue is likely more important than resolution.
The paper surface seems to limit the resolution rather than the scanner
or printer I am using.
Some QUESTIONS for Dan B. or others involved with making digital
negatives follow.
Is there a way to get more individual tones? And how is this done?
(The 300 I have gotten seem to be the limit I can get from Photoshop.)
How can the individual tones be spaced more effectively so as to provide
more even tonal discrimination through the range of values (light, mid,
and dark)?
What is the limit the inks may provide to the total number of tones?
How can the yellow ink be kept at a fixed level at larger values of
black ink?
I have seen many Pt/Pd prints made from digital negatives that appeared
fine, although I may not have looked that carefully. I have not seen
any of those prints along side a print from the original negative. This
may be that digital negatives are used to enlarge the size of the
image. I would suggest making a digital negative the same size as the
original and reproducing the original as close as practical, then
comparing prints from each. Are there differences in the highlights?
Is the substance identical? Do the prints breath the same life? These
are serious questions requiring serious answers.
-- Jeffrey D. Mathias http://home.att.net/~jeffrey.d.mathias/
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