| Re: CCD saturation [message #63118 is a reply to message #63022] |
Mon, 27 October 2008 06:27  |
pgrigis
Messages: 436
Registered: September 2007
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Senior Member |
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Wox wrote:
> Marshall Perrin wrote:
>
>> Shape detection is not the way to go here, versus detecting the level
>> at which pixels saturate. There should be some characteristic number of
>> counts per pixel below which you know data is not saturated.
>
> Yes, but this only works for the inner part of a saturated spot +
> streaks. The edges don't have a value of 65535 (it's a 16bit CCD
> camera) and can in fact have a lower value than non-saturated spots
> which I want to preserve.
Does the CCD really behaves this way? Seems pretty bad if
saturation is spread around that way... Are you sure it is not stray
light?
Paolo
That's why I could only think of shape
> detection to differ streaks from spots. However I'm not really able to
> do that. I usually remove a lot of non-saturated spots too.
>
> The problem I want to solve is illustrated here (X-ray Powder
> Diffraction): http://www.datasqueezesoftware.com/screenbig.jpg
> You see the so-called Debye rings in the image in the background and
> the azimuthally integrated pattern in the front. Usually you don't see
> this nice rings, but alot of spots forming a ring (or more rings).
> Imagine azimuthally integrating this when some spots are saturated
> with streaking. You don't end up with nice Gaussian peaks like in the
> figure, but some strange ..euhm.. things... that may look like peaks.
> If I could just detect the streaks and set these pixels to zero, I
> solved the problem.
>
> Since there are alot of astronomers here, I would think they also have
> similar problems to solve, only their spots are not scattered X-ray
> beams but stars :-).
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