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Re: kernel convolution? [message #49512]

Mon, 31 July 2006 08:45

James Kuyper
Messages: 425
Registered: March 2000

Senior Member

edward.s.meinel@aero.org wrote:
> No, a high-cut filter won't work. If you look at the FFT of a single
> star (star-->point-spread function, FFT(star)--> modulation transfer
> function), you will see that it contains information in ALL
> frequencies.

True; the best you can do by that method is to signficantly reduce and
spread out the brightness of the stars, not eliminate them entirely.

> Here's a couple of ways to remove stars:
>
> 1) determine the centroid of each star and subtract the appropriately
> weighted point-spread function.

Small statistical variations between the image and the best-fit
point-spread function will remain after performing such a subtraction.
Because the star is a bright source against a dark background, those
small residuals might be much brighter than the remaining background,
and unlike the low-frequency components left over from the high-cut
filter, they will be tightly centered around the original location of
the star. I can't say from personal experience whether those residuals
are a bigger problem than the residual low-frequency terms after using
a high-cut filter.

> or
> 2) apply a median window filter with a width of about twice the width
> of the star.

That sounds like it should work. You'll still pick up any long tails of
the PSF, but with a sufficiently large window, that should be a very
small effect.

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[Message index]

		Re: kernel convolution? By: James Kuyper on Mon, 31 July 2006 08:45
		Re: kernel convolution? By: edward.s.meinel@aero. on Mon, 31 July 2006 07:51
		Re: kernel convolution? By: James Kuyper on Fri, 28 July 2006 14:09
		Re: kernel convolution? By: adisn123 on Fri, 28 July 2006 13:07
		Re: kernel convolution? By: Tom S. on Fri, 28 July 2006 12:54

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