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Re: [OM] Digital top of the heap...

Subject: Re: [OM] Digital top of the heap...
From: "John Petrush" <petrush@xxxxxxxxxxxxx>
Date: Sat, 28 Nov 1998 12:08:43 -0800
"wonky"??  Is that a technical term <g>.
My limited understanding of CCD devices tells me the primary difference
between astronomical CCD cameras and "consumer" CCD's is the astro ones are
electronically cooled to very low temperatures to increase sensitivity and
reduce noise.  While I'm positive Lee can explain more accurately, with an
astro CCD one takes two exposures to get a picture - a "dark frame" and the
image itself.  The dark frame is all black, except for the noise patterns
for that CCD.  The dark frame values are then subtracted from the image
values to produce the first generation image.  I say first generation
because there is usually subsequent manipulation after the image is captured
and that manipulation depends entirely on what one's objectives are.

If you have image manipulation software (photoshop, gimp, ???) that can
register and subtract, take a dark frame and save it for reference.  Then
register it with an image, subtract and save.  You can then further modify
the resultant image for crop, color balance, etc.  I believe you will see
the artifact disappear.

John P
______________________________________
there is no "never" - just long periods of "not yet".
there is no "always" - just long periods of "so far"


>At 05:50 PM 11/27/98 -0500, Sebastien wrote:
>>
>>I don't know about Olympus, but the top consumer Kodak model (DC-260)
>>has a peculiar problem... It look's like an impressive light leak!
>>
>>I put an example at
>>    http://www.neci.nj.nec.com/homepages/sebastien/kodak
>>
>>Kodak customer support, usually prompt to answer, went really
>>silent on this one.  I might add that I've got two DC260 cameras
>>(for stereo shots) and they both behave the same way.
>>I guess Olympus could only be better than this.
>
>To which Garth replied:
>
>Is it possible that this is electrical noise, which normally is
unnoticeable because it's below a certain threshold?  I can't imagine that
CCDs can operate for upwards of a quarter of a minute, gathering light using
the buildup of electrical charges, without something wonky happening.  Just
a (relatively uneducated) guess.




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