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Re: correlation of single pixels [message #82029 is a reply to message #81971]

Mon, 12 November 2012 10:40

Klemen
Messages: 80
Registered: July 2009

Member

Hi Max,

no x and y are in this case just the regression variables. See:
https://groups.google.com/forum/?fromgroups=#!topic/comp.lan g.idl-pvwave/F2E8cLePGsQ

Computing correlation using IDL function CORRELATE is ok, if you have to do it once. But here you have to do it within each area of interest a couple of times (considering set of possible offsets in x and y direction) so you have to use 4 FOR loops which will run slow!

Thus you should ask yourself first, how large is the data set you want to process. If you are sure that your offset are not larger than 2 pixels, then you might go for the slow version. That would be something like:

results_corr = make_array(...
results_offx = make_array(...
results_offy = make_array(...
FOR xall=xstart,xend do begin
FOR yall=ystart,yend do begin
search_area = data[xall-search_size:yall+search_size]
template = data[xall-template_size:yall+template_size]
FOR xoff=-search_size:search_size do begin
FOR yoff=-search_size:search_size do begin
data = (shift(search_area, xoff, yoff))[right indeice]
corr = correlate(data[*], template[*])
if corr gt results_corr[xall, yall] then begin
results_corr[xall, yall] = corr
results_offx[xall, yall] = xoff
results_offy[xall, yall] = yoff
endif
endfor
endfor
endfor
endfor

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[Message index]

		correlation of single pixels By: haikoley on Mon, 05 November 2012 01:51
		Re: correlation of single pixels By: Klemen on Mon, 12 November 2012 10:40
		Re: correlation of single pixels By: haikoley on Mon, 12 November 2012 02:24
		Re: correlation of single pixels By: Klemen on Mon, 12 November 2012 10:28

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