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Re: Scanning glass negatives



Hello,

A few considerations and strategies in optical capture of glass
negatives:

- Most scanners are designed with a transparancy adaption layer,
which is designed for correcting the digitally calculated focal length
and resulting image dimensions of the captured bitmap. These
devices are specifically designed for the media variance of source
images that are not mounted to the outer contact interface between
the calibrated CCD or video line camera synthetic focal length, like
suspended matter such as emulsions e.g, negatives.

- Glass to glass contact should not cause scratches if both glass
surfaces are free of organic and inorganic matter (dirt), it is the dirt
the acts as an abrasive. If removing matter is not possible, silicon
spray applied to the glass surface with an optics cleaning rag will
dramatically reduce the possiblility of abrasion.

- Moire patterns only result in consistently isometric repeating
patterns that are processed at a varying frequency which creates
an effect of overlaying the pattern over other image elements with
the same isometry. Cross hatched and news print low resolution
dots and equidistant spacing between the dots often causes this
effect with CCDs and video line camera, although it tends to be
more common in video line cameras due to the lower frequency
analog signals and their vunerablity to overlapping, rather than
directly digitally processed output from the photosites of CCDs.


Michael B. Kennedy, D.Sc.
Chief Technology Officer
1-800-347-9310
mkenedy@imagepub.net
www.imagingprofessional.com
www.imagepub.net
www.kmprofessional.com
-------------------------------------------------------------
On 5 Jun 00, at 9:58, Steven Phalen wrote:

> Hello,
> I'm wondering if someone might have some advice for scanning glass plate
> negatives.  I'm wary of the glass-on-glass contact, so how can this be done
> effectively without scratches either to the scanner glass or the plates?
> Thought of mylar between but am concerned about the "moire"(sp?) effect.
>
> Also, I imagine that for quality reasons the emulsion should go down due to
> the thickness of the glass.
>
> Any advice here is greatly appreciated!
> (Please copy me on replies since I don't subscribe to the list at this time)
>
>         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>           Steven L. Phalen
>           Library Specialist Senior
>           Dept. of Archives & Manuscripts
>           Arizona State University
>           Phone:(480)965-2544; Fax:(480)965-9169
>           E-mail:thirteen@mainex1.asu.edu
>         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>
>
>

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