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Re: CONVOL with 2D array and 1D kernel [message #52981 is a reply to message #52972]

Fri, 09 March 2007 06:42

David Fanning
Messages: 11724
Registered: August 2001

Senior Member

Eric Hudson writes:

> Also, there seems to be a lot of confusion about what CONVOL really
> does. Is there a definitive, readable, source so I can make sure that
> I'm really doing what I want here (a true mathematical convolution
> where I've made the array a bit bigger on the edges by duplicating the
> top & bottom rows, done the convolution, and then chopped off the
> edges to minimize edge effects).

I'm no convolution expert, but the documentation is
pretty clear that if you want to do a convolution in
a "mathematical" sense (as you appear to do), then you
are going to have to explicitly set the CENTER keyword
to zero. Otherwise, you are going to do a convolution
in an "image processing" sense, which may not be what
you had in mind.

Also, have you expanded the 2D array yourself, or are
you hoping IDL is going to do that for you? If you did
it yourself, is it possible some of the values are not
what you think they are?

Cheers,

David
--
David Fanning, Ph.D.
Fanning Software Consulting, Inc.
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Sepore ma de ni thui. ("Perhaps thou speakest truth.")

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[Message index]

		Re: CONVOL with 2D array and 1D kernel By: David Fanning on Fri, 09 March 2007 09:52
		Re: CONVOL with 2D array and 1D kernel By: Eric Hudson on Fri, 09 March 2007 09:38
		Re: CONVOL with 2D array and 1D kernel By: David Fanning on Fri, 09 March 2007 06:42

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