From: Tod Gangler (email@example.com)
Date: 02/25/01-02:08:35 PM Z
Greetings Garet and Neal,
>Are the stochastic negatives producing a continuous tone image on your gelatin
>emulsions? Or are you getting dots?
Images look continuous tone, but dots are visible with a loupe or a
microscope. With a loupe, they look like film grain, and are usually
defining the grain of the original negative or transparency. They reveal
themselves as stochastic digital spots under a 25x microscope.
>It would seem like imperfect contact should soften the image and make the
>transitions MORE smooth (dot edges less sharp).
Yes, and its not a problem until one either wants to print something gray
with a tri-color or four color process, or one wants repeatable results.
>I too have noticed a lot of variation in imagesetter output of stochastic
>screened digital negatives, even of the same file
>Are you using Icefields software, the Photoshop bitmap or a proprietary
I'm using Icefields. Agfa's Crystal Raster program or Dan Burkholder's
Photoshop bit-map method are pretty good, too. Most of the other
proprietary stochastic screening RIPs (Diamond Screen, Scitex Full-Tone,
etc.) that I've tried have all been quite lacking- coarse and gritty
looking, even when generating quite small spots.
The imagesetter hardware is a big variable, and there is a large difference
in the potential of the different brands of machines. It gets complicated
quickly, as each kind of machine (Scitex, Fuji, Agfa, etc,) can come in a
variety of models offering different resolutions, and can be installed with
different RIPs all having their own effect on the output. Banding can come
from film, processing, hardware (too light weight or poor lazer calibration
or focus,) or issues relating to the RIP. Some RIPs re-interpolate the
file, or have memory, buffer or "streaming speed" issues which can cause a
problem with the final output, too.
I've gotten best results on drum design imagesetters, like the Agfa Avantra
series, or the newer Fuji Celix machines. Even two identical devices
installed in two different shops can give different results, though. I,
too have had problems using the highest device resolution on some
imagesetters, getting banding just like you describe. But then the same
model machine in a different shop might perform flawlessly at this
resolution. I think its called fraught. Many shops use the newer High
D-Max films (with developer incorporated) designed to make a harder-edged
dot which is easier to plate or print in offset printing, but I think that
those films often produce streaking or banding when we try to imageset only
these small stochastic spots. The older imagesetter films without the
incorporated developer work much better for stochastic negs for alt-photo
use, for me.
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