Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!bu.edu!wang!wdr
From: wdr@wang.com (William Ricker)
Newsgroups: comp.graphics
Subject: Re: Can handheld scanners scan BACKLIT images?
Message-ID: <b7j9ou.dg2@wang.com>
Date: 24 Jun 91 17:24:30 GMT
References: <2835@umriscc.isc.umr.edu>
Organization: Wang Labs, Lowell MA, USA
Lines: 37

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).
3.  You could probably disable the light source (you might have to replace
    it with a resistor, if the software is smart enough to sense a burnt
    out light and give error).  Yet again, you'll use the contrast knob
    to correctly bias the sensor.

I've had some fun with the Logitech ScanMan256(tm) hand scanner with
256-grey scales, although for large tasks I'm sure I'd prefer my
firm's power-feed flat-bed scanners.  (And I hear we've got some new
stuff in the works that blows both kinds away.)

I would be careful of one thing: scratching your emulsion with the scanner.
I don't know if Xrays have the image on the 'front' or 'back' of the carrier;
if the image is on the 'front', you might want to scan through the 'back' and
reverse the image in software to protect the emulsion.  Alternatively, you
could see if the Xray lab has a clear-coat to protect the emulsion -- they
may instinctively use it, or only on request; I know Polaroid used to sell
such. 
-- 
/s/ Bill Ricker                wdr@wang.wang.com 
"The Freedom of the Press belongs to those who own one."
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