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Re: find bimodal maximum in each row [message #74891 is a reply to message #74884]

Fri, 04 February 2011 12:57

Jeremy Bailin
Messages: 618
Registered: April 2008

Senior Member

On Friday, February 4, 2011 4:02:47 AM UTC-5, vijay wrote:
> I have an array of 512x512 and for each row there is a
> bimodal like peak. I want to find this peak in each row (ex. first
> peak value 177 and second peak value 244, etc). Like that each row
> will have two different peak
> values. How to obtain these peak values for the whole array and result
> them in new array.

If you can guarantee that the peaks will not occur in the first or last column of each row, this will give you every single local maximum:

q = [[0,1,2,1,2,1,0], [1,2,0,0,2,2,0], [0,2,2,2,0,1,0]]
nx = (size(q, /dimen))[0]

; is this a local maximum? (note that the index starts at element 1,* of q)
peakp = (q[1:nx-2,*] gt q[2:nx-1,*]) and (q[0:nx-3,*] le q[1:nx-2,*])
; where is that true?
peaklocations = where(peakp)
; turn into array locations into peakp
peaklocations_xy = array_indices(peakp, peaklocations)
; increment the x coordinate because peakp is shifted one element to the right of q
peaklocations[0,*]++
; what are the values of q there?
peakvals = q[peaklocations_xy[0,*], peaklocations_xy[1,*]]

IDL> print, peaklocations_xy
2 0
4 0
1 1
5 1
3 2
5 2
IDL> print, peakvals
2
2
2
2
2
1

Note that it will pick up every single local maximum, regardless of how many there are per row.

-Jeremy.

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[Message index]

		Re: find bimodal maximum in each row By: Jeremy Bailin on Sun, 06 February 2011 12:27
		Re: find bimodal maximum in each row By: vijay on Fri, 04 February 2011 19:32
		Re: find bimodal maximum in each row By: Jeremy Bailin on Fri, 04 February 2011 12:57

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