Newsgroups: comp.graphics
Path: utzoo!utgpu!cunews!bnrgate!bigsur!bcars53!mussar
From: mussar@bcars53.uucp (G. Mussar)
Subject: Re: Can handheld scanners scan BACKLIT images?
Message-ID: <1991Jun25.161012.25370@bigsur.uucp>
Sender: news@bigsur.uucp
Reply-To: mussar@bnr.ca (G. Mussar)
Organization: Bell-Northern Research, Ottawa, Canada
References: <2835@umriscc.isc.umr.edu> <b7j9ou.dg2@wang.com> <4993@gmdzi.gmd.de>
Date: Tue, 25 Jun 91 16:10:12 GMT


In article <4993@gmdzi.gmd.de> strobl@gmdzi.gmd.de (Wolfgang Strobl) writes:
>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.

I've tried scanning slides with my Scanman 256. The white paper trick didn't
work, but, back lighting did. It is quite sensitive to the quantity of light
(in particular, it is very sensitive to infared). In addition, any kind of
florescent lighting causes light and dark bars since they turn off and on
120 times per sec. I found the best way to go was to illuminate a white
paper that was place about 1 foot behind the slide and to use a DC powered
light.
--
-------------------------------------------------------------------------------
Gary Mussar  |Internet:  mussar@bnr.ca                |  Phone: (613) 763-4937
BNR Ltd.     |                                        |  FAX:   (613) 763-2626
