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Re: flux-conserving image resampling? [message #47696 is a reply to message #47689]

Fri, 24 February 2006 01:03

Bringfried Stecklum is currently offline

Bringfried Stecklum
Messages: 75
Registered: January 1996

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Marshall Perrin wrote:
> Bringfried Stecklum <stecklum@tls-tautenburg.de> wrote:
>
>> I did not check how well it preserves the flux. In any case, you can
>> force the total flux of the output image to be the same as that of the
>> input image.
>
>
> As Henry points out, this isn't really sufficient to ensure that the
> original flux stays in the right parts of the final image. That's important
> for my particular application, which is a dual-beam differential polarimeter.
> I'm trying to take a very precise difference between two images of
> the same star taken simultaneously on different parts of the detector,
> and thus merely enforcing total flux conservation lets light slop between
> the two stellar images (and the background too). Yes, it's a small effect,
> but I'm trying to -measure- a fairly small difference in the first place and
> thus care about this.
>
> - Marshall

Ah, I see your point. I guess what has to be done is to account for the
difference in pixel size between the original and the corrected image.
The code I've written only does resampling on a grid which represents
the pixel location of the undistorted image. In order to preserve the
flux locally, one has to keep in mind that depending on the distortion
one pixel of the corrected image will subtend an area of less or more than
one pixel in the original image. Well, I'm not talking about sub-pixels here
(we had this earlier in the group...). For instance in the simple case of a
Wollaston which has slightly different image scales for the O and E beams,
the ratio of those scales should be applied after one image has been
registered to the other. In some sense this photometric correction can
be considered as distortion flatfield.

- Bringfried

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[Message index]

		Re: flux-conserving image resampling? By: edward.s.meinel@aero. on Fri, 24 February 2006 08:04
		Re: flux-conserving image resampling? By: Bringfried Stecklum on Fri, 24 February 2006 01:03
		Re: flux-conserving image resampling? By: Marshall Perrin on Thu, 23 February 2006 09:39
		Re: flux-conserving image resampling? By: henrygroe on Thu, 23 February 2006 08:00
		Re: flux-conserving image resampling? By: Bringfried Stecklum on Thu, 23 February 2006 00:32

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