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Re: Need help reconstructing flat-field. Minimization problem. [message #56393 is a reply to message #56390] Wed, 24 October 2007 01:46 Go to previous messageGo to previous message
Tal is currently offline  Tal
Messages: 26
Registered: August 2007
Junior Member
>> Apart from the fact that it returned junk, the algorithm seemed OK.

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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