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Re: perimeter of a blob [message #18768 is a reply to message #18634]

Thu, 27 January 2000 00:00

Richard Adams
Messages: 9
Registered: January 2000

Junior Member

Dear Ben, if you just need the indices and not the indices in order around
the perimeter then you could use an imaging method like this:

a = your image; assume it is one blob and has value 255 as object
otherwise 0
bb = convol(a, replicate(1,3,3), 9, /center); change the kernel if you
want some other connectivity
edges = where(bb gt 0 and bb lt 255); these are edges of your blob both
inside and out

bb[*] = 0
bb[edges] = 255 ; make this new image just edges
bb = A AND BB ; now keep just those edges inside your object
perimeter = where(bb eq 255); these are indices to final outline

I think this works - does at least on dumb test images. If you want them in
order then I guess you could trace around with a maze-search algorithm. Big
disadvantage is that you need to isolate a blob at a time, I think.
Interested to hear if it works around all your corners.

Richard.

--
Richard J Adams }<}}}}ï¿½> e: r.j.adams@bath.ac.uk
MRC Senior Research Fellow t: +44 1225 826436
Department of Biology and Biochemistry f: +44 1225 826779
University of Bath, Bath, BA2 7AY, UK

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[Message index]

		perimeter of a blob By: Ben Tupper on Wed, 26 January 2000 00:00
		Re: perimeter of a blob By: Ben Tupper on Thu, 27 January 2000 00:00
		Re: perimeter of a blob By: davidf on Thu, 27 January 2000 00:00
		Re: perimeter of a blob By: Richard Adams on Thu, 27 January 2000 00:00

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