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Re: Rapid "moving windows" access in IDL? [message #37846 is a reply to message #37845]

Thu, 29 January 2004 20:33

mchinand
Messages: 66
Registered: September 1996

Member

In article <BC3EF6CE.18DB4%greenberg@ucdavis.edu>,
Jonathan Greenberg <greenberg@ucdavis.edu> wrote:
> I'm trying to code a semivariance measure to analyze an image in IDL. Since
> the call requires extracting data from a matrix a certain distance away from
> the center pixel, is there a fast way of coding IDL to extract these
> locations, or is am I doomed to have a very slow algorithm. Basic gist:
>
> For a given pixel/matrix location, subtract off the value of the pixels
> surrounding that pixel:
>
> For pixel at A is at x,y
> B at x-1,y
> C at x+1,y
>
> Semivariance = ((A-B)^2 + (A-C)^2)/4
>
> Any suggestions?
>
> --j
>

I'm not sure if this will be faster, but one option is to create B and C
arrays using SHIFT:

B=shift(A,-1,0)
C=shift(B,1,0)

sv= ((A-B)^2 + (A-C)^2)/4

Obviously, this method is more memory intensive than looping through
A. The edge values probably won't be what you want either.

--Mike

--
Michael Chinander
m-chinander@uchicago.edu
Department of Radiology
University of Chicago

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[Message index]

		Re: Rapid "moving windows" access in IDL? By: Craig Markwardt on Fri, 30 January 2004 14:55
		Re: Rapid "moving windows" access in IDL? By: Chris Lee on Fri, 30 January 2004 06:09
		Re: Rapid "moving windows" access in IDL? By: Jonathan Greenberg on Fri, 30 January 2004 03:15
		Re: Rapid "moving windows" access in IDL? By: Craig Markwardt on Thu, 29 January 2004 22:01
		Re: Rapid "moving windows" access in IDL? By: mchinand on Thu, 29 January 2004 20:33
		Re: Rapid "moving windows" access in IDL? By: Jaco van Gorkom on Sun, 01 February 2004 14:20

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