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Re: coherence test implementation [message #15421 is a reply to message #15336]

Thu, 13 May 1999 00:00

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

Mark Rehbein <mrehbein@aims.gov.au> writes:
>
> Hi,
>
> I'm doing some cloud detection on some rather large images using what
> some people call a coherence test. To do a coherence test on a pixel
> you take a 3x3 matrix around that pixel and assign that pixel the
> standard deviation of the 3x3 matrix. I have implemented this the
> following way:
>
> for y=1, lines-1 do begin
> for x=1, pixels-1 do begin
> ...

As the two posters graciously have demonstrated, they were able to
partially vectorize the algorithm. However, because your procedure
involves *overlapping* portions of the same array, it will never be
possible to fully vectorize it.

Explicit FOR loops are not bad if the work done during one iteration
takes longer than the overhead time with the loop. Of course, that
rule of thumb is somewhat CPU dependent.

Craig

--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@astrog.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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[Message index]

		coherence test implementation By: Mark Rehbein on Thu, 13 May 1999 00:00
		Re: coherence test implementation By: Struan Gray on Thu, 13 May 1999 00:00
		Re: coherence test implementation By: eddie haskell on Thu, 13 May 1999 00:00
		Re: coherence test implementation By: Dick Jackson on Thu, 13 May 1999 00:00
		Re: coherence test implementation By: Craig Markwardt on Thu, 13 May 1999 00:00
		Re: coherence test implementation By: Dick Jackson on Thu, 13 May 1999 00:00

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