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Re: coherence test implementation [message #15415 is a reply to message #15336]

Thu, 13 May 1999 00:00

Struan Gray
Messages: 178
Registered: December 1995

Senior Member

Craig Markwardt, craigmnet@cow.physics.wisc.edu writes:

> 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.

True, but you can always use the built-in function CONVOL with a
kernal full of ones to do the local-area averaging. My IDL is
installed elsewhere, so I can't check my code, but the following
should give the right idea:

kernal = intarr(3,3)
kernal[*] = 1
squaremean = convol(image*image, kernal, total(kernal))
mean = convol(image, kernal, total(kernal))
standard_dev = sqrt(squaremean - mean*mean)

The nice thing about this method (in addition to running at native
speeds) is that it is easily scaleable to larger kernals, and convol
handles edge effects for you. The downside is that for big images it
can soak up memory, especially if you convert the image to the
next-largest data type in order to side-step data overflow problems.

Struan

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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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