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Re: Need help reconstructing flat-field. Minimization problem. [message #56390 is a reply to message #56383]

Wed, 24 October 2007 07:51

JJ
Messages: 36
Registered: January 2007

Member

Thanks,

But unfortunately that doesn't get me any closer to the solution. I
basically already have the dark-corrected image. Removing the dark
current (which I am more familiar with that I want to be - believe me)
does not remove the shot noise, which scales with the square root of the
# photons hitting the pixel. This noise is I believe the result of the
quantum nature of light. So imaging the same exact point twice under
the same exact conditions even with a perfect camera will give you
different results.

Just for argument's sake, let's assume that the dark current is 0 and
our camera is perfectly noiseless. Our CCD pixel increments by one
count for every 50 photons that hit it. For a pixel value around 2000,
you still get a shot noise of +/- sqrt(2000 * 50) / 50, which gives
roughly 2000 +/- 6 (I think that's 1 sigma).

You can't get rid of or model the shot noise because it's truly random.
And because of that, I believe that my problem requires a
minimization solution - or at least a solution that does not multiply
this noise into huge errors as it progresses, as my solution seems to.

Thanks.

-Jonathan

Tal wrote:

>
> sounds familiar.
> :- )
>
> Hi Jonathan,
>
> If i got all this right then there is one thing missing here: Dark
> current images. Take image for the same location of your light images
> 1,2,3 but with the shutter closed. You will record in fact the noise
> of your camera. an integration of heat, electronics, inter-CCD
> variabilities in response etc.
>
> now all you need to do is generally: (light_image - dark_image)
> and continue from there as usual. since your CCD camera is a 2D CCD
> array, following your notation the ratio is now:
>
> img'=(img-dark)
> img'1[x1,y1] / img'2[x2,y2] = R'[x1,y1,x2,y2]
>
> where R' is the dark-corrected Ratio image R.
>
> to be on the safe side, repeat your light measurements and dark
> measurements again if possible, since dark-current images are variable
> in time according to conditions during acquisition.
>
> hope this helps,
> Tal
>
>

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[Message index]

		Re: Need help reconstructing flat-field. Minimization problem. By: b_gom on Wed, 24 October 2007 11:26
		Re: Need help reconstructing flat-field. Minimization problem. By: JJ on Wed, 24 October 2007 07:51
		Re: Need help reconstructing flat-field. Minimization problem. By: Tal on Wed, 24 October 2007 01:46
		Re: Need help reconstructing flat-field. Minimization problem. By: pgrigis on Thu, 25 October 2007 01:13
		Re: Need help reconstructing flat-field. Minimization problem. By: jdshaw on Wed, 24 October 2007 14:06
		Re: Need help reconstructing flat-field. Minimization problem. By: JJ on Wed, 24 October 2007 13:45
		Re: Need help reconstructing flat-field. Minimization problem. By: JJ on Wed, 24 October 2007 13:44

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