| Re: Non maxima supression [message #51582] |
Mon, 27 November 2006 13:01 |
Jean H.
Messages: 472
Registered: July 2006
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Senior Member |
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Charudatta Phatak wrote:
> Hello,
>
> I want to do a non maxima supression on a 2d array within a specified
> neighborhood of pixels. The way i am doing it right now is looping over
> all the pixels and check if the value is max in the 5x5 neighborhood. if
> it is max then keep it or else set it to zero. Is there a IDL way to do
> it faster than 2 for loops?
>
> thanx
>
> cheers,
> -cd
You can vectorize this.
neighborhood = [-9,-1,1,9] ;In this example, a Von Newman neighborhood
centered on the cell [0] of a 10 * x array. Do NOT keep the "central"
cell index.
data = ... ;your 2D array
neighborhoodIndices = neighborhood + indgen(n_elements(data)) ;If you
want to omit some pixels, like on the edge, put an array of valid
indices instead of the indgen().
neighborhoodValues = data[neighborhoodIndices]
sortedNeighbIndices = sort_ND(neighborhoodValues,1) ;Get sort_ND from
the web or from JD..
highestValue =
neighborhoodValues[sortedNeighbIndices[n_elements(neighborho od)-1, *]]
writeZeroAt = where(neighborhoodValues gt data)
data[writeZeroAt] = 0
Jean
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| Re: Non maxima supression [message #51585 is a reply to message #51582] |
Mon, 27 November 2006 11:09  |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Charudatta Phatak writes:
> I want to do a non maxima supression on a 2d array within a specified
> neighborhood of pixels. The way i am doing it right now is looping over
> all the pixels and check if the value is max in the 5x5 neighborhood. if
> it is max then keep it or else set it to zero. Is there a IDL way to do
> it faster than 2 for loops?
Can you use any of the lessons learned in this "maximum value
array resampling" article:
http//www.dfanning.com/idl_way/maxresample.html
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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