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From: Chuck Simmons
Organization: You jest.
X-Mailer: Mozilla 4.61 [en] (X11; U; Linux 2.0.33 i586)
Subject: Re: Increasing IR LED Output
References: <3D9F5B9E.70DB3C27@apt0.sao.arizona.edu> <3D9F8489.9FE65295@webaccess.net> <3D9FADEE.D3713FC5@apt0.sao.arizona.edu>
Date: Sun, 06 Oct 2002 12:37:26 GMT
NNTP-Posting-Date: Sun, 06 Oct 2002 05:37:26 PDT
Louis Boyd wrote:
> Chuck Simmons wrote:
> > Louis Boyd wrote:
> > >
> > > A better approach is to mathematically add adjacent frames to reduce
> > > noise. For example, display the sum of the last 20 fields. (1/3 sec).
> > > Some additional smearing will occur but isn't particularly annoying to
> > > watch. Cooling the CCD with thermoelectrics will reduce noise allowing
> > > higher gain. Some security cameras use these techniques.
> > Perhaps I am a bit off of the wavelength you are on but mathematically
> > adding frames is not as good for reducing noise as integrating on the
> > CCD itself. If the CCD is capable of slow scanning (most are), it would
> > be better to scan and grab one frame every 1/3 second than to grab the
> > sum of 20 frames (this assumes industrial sync with 60 frames per second
> > rather than TV which is 30). Moreover, this technique only reduces noise
> > in the stationary background. Moving objects are not as much improved.
> > Have I missed something?
> I agree that you usually get a better image by integrating on the chip,
> at least if thermal defects aren't dominant. However, for human viewing
> having the image change every 1/3 second or so is quite annoying. The
> method of adding new frames and dropping old one is still changing 30
> times a second so the eye tends to smooth the changes. Yes, it looks a
> bit "wormy" because the noise patterns have persistance. With memory
> (required for chip integration and adding multiple frames) it's also
> practical to remove any static defects, such as hot pixels and "clocking
> noise" which can help a lot.
> Moving objects, if viewed with a "strobed" LED will give a series of
> overlapping clear images rather than a smear. That can work with either
> on chip integration or memory integration and makes easier to see what
> the object was and estimate it's velocity and direction. None of these
> approaches beats having adequate lighting and continous frames faster
> than the eye's flicker response rate.
> Another way (perhaps obvious) to perk up the sensitivity of a CCD camera
> is to use a faster lens. The penalty is cost and reduction of depth of
> Lou Boyd
Thanks. I wasn't sure we were quite on the same page. We seem to be. I
am embarrassed that it took me half an hour to show that integrating on
a CCD is better than integrating off chip. Alzheimers I guess.
... The times have been,
That, when the brains were out,
the man would die. ... Macbeth
Chuck Simmons firstname.lastname@example.org
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