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From: strobl@gmdzi.gmd.de (Wolfgang Strobl)
Newsgroups: comp.graphics
Subject: Re: Can handheld scanners scan BACKLIT images?
Message-ID: <4993@gmdzi.gmd.de>
Date: 25 Jun 91 08:39:23 GMT
References: <2835@umriscc.isc.umr.edu> <b7j9ou.dg2@wang.com>
Organization: GMD, St. Augustin, F.R. Germany
Lines: 33

wdr@wang.com (William Ricker) writes:

>bkirby@cs.umr.edu (Bill Kirby) writes:
>>My concern is light source.  If scanners (and remember I know nothing
>>about scanners :-) have an internal light source, would that interfere
>>with an image that was being lit from behind?

>Hand-scanners have internal light, at least all I've seen.

>1.  Some scanners have an adjustable contrast knob (eg Logitech ScanMan 256).
>    twisting this may force it to ignore one source or the other.  Try it.

>2.  The internal light may be sufficient, if you back the transparency
>    with a solid white ground -- eg, oversize white paper.  Just because
>    *you* view Xrays on a light-box doesn't mean the scanner is restricted
>    to viewing the Xray negative in that position.  This will again call
>    for twisting the contrast knob, as double filtering in grey areas will
>    seriously shift the contrast curve (as I found out photocopying B&W
>    tone transparencies).

I tried this with the Logitech ScanMan 256 I bought last week, with
mixed success. The thing I tried to do was to scan 24*36mm b&w negatives
for previewing (one of my hobbies is b&w photographing, including all
the dark room processing) and for archiving purposes.

While putting the negative strip on a white paper and scanning it with
contrast set to dark and dpi to 400 works quite well for normal and
light negatives, it doesn't work at all for pictures where the interesting
details are in the darker parts of the negative.

Scanning color negatives didn't work at all.

Wolfgang Strobl