[filmscanners] RE: Vuescan and multipass algorithm

["" <ake.vinberg@home.se>]

Michael,

It seems that CCD dark current noise is always on top of CCD signal - unlike
for example sound noise, which by necessity must average to zero. So
averaging CCD samples will approach signal plus average noise value. Dark
current noise is also related to temperature - after a few hours powered on,
my cheap scanner is practically useless with slides, Dmax is down to 1
(average in dark areas is 10% of 255).

Then again, I am not an expert in this field, so perhaps I just got it
backwards.

It's probably better if I upload a few illustration images on my web and
post the links here - I'll post another reply later.

/Åke

-----Original Message-----
From: filmscanners_owner@halftone.co.uk
[mailto:filmscanners_owner@halftone.co.uk]On Behalf Of michael shaffer
Sent: Friday, May 03, 2002 2:11 PM
To: ake.vinberg@home.se
Subject: [filmscanners] RE: Vuescan and multipass algorithm


Åke writes ...

> ...
> The output images seem to be calculated by averaging the value
> in each pixel. The result is a

  What do you mean ... "smooth noise level, but no real noise elimination."?
Averaging really should eliminate noise.  That is, averaging is a result of
"adding" and normalization ... i.e., adding noise to noise always tends
towards less noise ... unless it really isn't noise.  Are you sure it isn't
something ... e.g., film grain?

> ...
> So: It would be great to have the option in Vuescan to choose
> algorithm in multipass scans, between Average and Minimum.

  I wish Vs would simply "add" the scans ... e.g., 4 10bit scans becomes
12bits, ... 8 12bit scans becomes 16bits.

cheerios ... shAf  :o)
Avalon Peninsula, Newfoundland
www.micro-investigations.com (in progress)

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