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Subject: [M]: Re: Pictor 208XT as an Autoguider
From: Tom Krajci
Reply To: mapug@shore.net
Date: Mon Oct 28 03:01:50 1996

This response is slightly off topic, but may be of use to many people
in this group.
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>From: anderson@goodnet.com (Howard C. Anderson)

>I would really like to post some current photo's on a home page
>I have constructed but I am shooting slides and have not yet found an
>affordable way to digitize the images decently. I tried one of the
>local services here in town - the digitized images came out mostly
>black. Really suppressed subjects of the photos, Trifid, Whirlpool,
>etc.
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Hi, Howard!

I had a similar experience digitizing slides and the first attempts
did come out dark like yours. What I had to do was make an
internegative copy of the slides and scan the negative image.

Why? If you scan the slides, the "sky background" is very dark.
Perhaps the pixel value (from 0 to 255) is 10. If the faint
nebulosity is about 10% lighter, it will be a pixel value of 11. Gee,
no big difference here to tease out subtle details.

If you scan a negative the sky background will give a high pixel
value, perhaps 200. If the nebulosity is 10% darker, it's value will
be about 180. In this case you get a 20 pixel difference whcih is
much better than the above situation.

I don't know of any other way around this problem with scanning
slides (it just seems to be the nature of the beast), unless you have
a 12 or 16 bit scanner at your disposal?!?

Tom Krajci
B-52 Intelligence Officer
http://spur.barksdale.af.mil