Digital negatives

CHPalmer@aol.com
Thu, 21 Mar 1996 23:16:53 -0500

As there seems to be more and more digital talk on this list, I thought I
might share my experiences with the group. I am a platinum/palladium
printer; I have not worked with other old processes, so I can't comment on
how my techniques would translate to gum/cyanotype/etc. About 15 months ago,
I began working with Rich Latour and Bill Nordstrom at EverColor to produce
digital negatives optimized for the platinum/palladium process. I'm sure that
many of you are familiar with their primary work, which is the production of
archival color prints using digital techniques and a process which is quite
similar to tri-color carbon. All of the work at my end was done with
PhotoShop on a Mac. We finished the development work last summer, and I have
been quite pleased with the results.

Briefly, the negative made by EverColor from my PhotoShop files is a 400 LPI
halftone, which is considerably finer than the 150 to 200 LPI output from
many service bureaus. They can make negatives up to 24"x36". EverColor
uses a Scitex ImageSetter to make the negative, which is on silver-based film
and thus lacks the permanence problem of digital negatives output through an
Iris printer. The dot pattern is very fine. With the unaided eye, you
cannot discern dots in the print; dots can be seen in lighter tonal areas
only with the aid of a loupe. We did not use the Diffusion Dither Bitmap
method which is mentioned in Dan Burkholder's excellent book. I have tried
negatives with both the 400 LPI linescreen and 1200 DPI Diffusion Dither
Bitmap; I can (with the unaided eye) discern no significant difference
between them regarding apparent sharpness, "dotty" appearance, etc.

The characteristic curve of the film (if there is such a thing for a digital
negative!!) is pretty close to a straight line. The DMax of the negative
(corresponding to a PhotoShop density of 1% in the positive image) is 2.0,
while the DMin (PhotoShop density 100% in the positive) is 0.10; so, the
usuable "dynamic range" of the negative is about 1.90. The film base + fog
of the material is 0.05, less than most conventional "analog" films.

Using this curve, calibration of my monitor with final prints has been quite
easy, within the confines of trying to compare a luminous image (the monitor)
with a reflected-light image (the print): what I see on the monitor is
pretty much what I see on the final print.

If any list members are interested, I would be happy to share all of the
information I have about this process, including a graph/chart illustrating
the "curve" of the digital negative material.

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Regarding the recent discussion regarding making digital negatives with a
laser printer, I have two questions/comments:

First, has anybody tried using a 1200 DPI laser printer for outputting
negatives? I'm told that some of the better equipped print/xerox shops (such
as Kinko's in the US) have these printers and will make prints (or
transparencies) from your digital files for a few dollars each.
Theoretically, these printers should give considerably higher resolution for
grayscale material than the usual 300 or 600 DPI laser.

Second, regarding the comments that laser printer output has insufficient
contrast for old processes: It seems like it shouldn't be too much trouble
to output a film positive from the laser printer, then contact print onto a
high-contrast film to increase the contrast. Has anybody tried this?

Charlie Palmer
Albuquerque, NM