Digital negatives

ODSRARN5.ASTRAUS (ASTRAUS@ODSRARN5.SSW.JNJ.COM)
25 Jun 1996 09:43:09 GMT

Date: Mon, 24 Jun 1996 09:03:56 -0700 (PDT)
From: beakman@netcom.com (Beakman)
To: alt-photo-process@cse.unsw.edu.au
Subject: Digital negatives
Message-ID: <199606241603.JAA19940@netcom21.netcom.com>

On Moday, June 24th David wrote

>I've been doing some interesting tests with digital negatives recently
>and I can now definitely recommend halftone linescreens rather than the
>diffusion dither bitmaps recommended by Dan Burkholder. They print much
>smoother, especially useful for broad monotone areas.

>On a more interesting note however, I have noticed that it appears that my
>prints from these digital negs are composed of more than just the black
>haltone dots. This is very strange, and I don't understand it so I was
>hoping someone else might have some insight. Let me elaborate...

>I take my digital neg which is composed entirely of clear dots in an
>appropriate pattern. I would expect that, when looked at with a loupe,
>the final print would look like just a bunch of black dots. However,
>what I find is that it actually looks like someone exposed the paper to a
>continous tone negative which laid down swatches of tone (but no detail)
>and then printed the black dots on top of that. Weird. My father, who
>has been working in the printing industry for 35 years confirmed what I
saw.

>As a specific example, those of you that double-coat you paper know what
>it's like when part of the image prints on an area that has just a single
>coat. The single-coated area prints a stop or two darker than the
>surrounding double-coated part. Well, suppose this occurs in a broad area
>of continous tone, such as a sky. If you look at the transition between
>the two with a loupe, the halftone dots are exactly the same size in both
>the single and double-coated areas, but the smooth, continous tone
>*background* is darker in the single-coated area. Now to my way of
>thinking there should be no "background" just the halftone dots. This
>seems to occur in the normal print area as well, and is *not* related to
>the single/double coating.

>So, what's going on? Is my digital neg acting as both a continous tone
>neg and a digital one at the same time somehow.

>Stanger than fictiion

David,

I have noticed the same effect. This must be the reason that Dan Burkholder
writes about varying the exposure to get different effects. If the negative
was
purely clear dots on black, the effect would be the same within a broad
range
of exposures. My hypothesis is that there is some light diffusing from the
dots.
My light source is a bank of flourescent bulbs so that the light penetrates
each
clear dot at many different angles. Since the paper has a texture the film
is not
in intimate contact with the entire surface. This is somewhat analagous to
dot
spread in printing.