| Re: Help With Finding Local Maxima of an Image (locmax) [message #65826] |
Thu, 26 March 2009 06:20  |
Jeremy Bailin
Messages: 618
Registered: April 2008
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Senior Member |
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On Mar 25, 3:35 pm, einszweil...@gmail.com wrote:
> I'm trying to use R. Sterner's "locmax" function (see below) to find
> local maxima (peaks of intensities) in an image. I'm a bit of a
> newbie to IDL so forgive me if my questions are silly :)
>
> As far as I can tell, all I need to do is read in the image (img) and
> use the command "locmax, img". Is that correct?
>
> When I do this I get the error message which says something like
> "return statements in functions must have 1 value" Line 79 (i.e. the
> second to last line below with the "return" statement).
>
> What's going wrong here? Why is the function trying to return
> multiple values? Isn't that what it's supposed to do - return all of
> the places where there's a local max?
>
> Can anyone help me with this? Does anyone know of any other
> procedures/functions which do similar things?
>
> Thanks.
>
> ;----------------------------------------------------------- --
> ;+
> ; NAME:
> ; LOCMAX
> ; PURPOSE:
> ; Find local maxima in an image.
> ; CATEGORY:
> ; CALLING SEQUENCE:
> ; locmax, img
> ; INPUTS:
> ; img = image to process. in
> ; KEYWORD PARAMETERS:
> ; Keywords:
> ; MASK=m returns a mask image with 1 at all
> ; local maxima and 0 elsewhere.
> ; WHERE=w returns 1-d indices of all local maxima.
> ; -1 if no local maxima.
> ; VALUES=v returns values of img at all local maxima.
> ; VALUE_IMAGE=vimg use vimg to determine values.
> ; Instead of img.
> ; IX=ix returns x index of all local maxima.
> ; IY=iy returns y index of all local maxima.
> ; /SORT sorts local maxima by descending image values.
> ; /NOEDGE ingores any maxima at image edges.
> ; OUTPUTS:
> ; COMMON BLOCKS:
> ; NOTES:
> ; Notes: All output is through keywords.
> ; Ignores plateaus. May not work for
> ; all edge points.
> ; MODIFICATION HISTORY:
> ; R. Sterner, 17 Aug, 1990
> ; R. Sterner, 27 Aug, 1990 --- added value_image.
> ;
> ; Copyright (C) 1990, Johns Hopkins University/Applied Physics
> Laboratory
> ; This software may be used, copied, or redistributed as long as it is
> not
> ; sold and this copyright notice is reproduced on each copy made.
> This
> ; routine is provided as is without any express or implied warranties
> ; whatsoever. Other limitations apply as described in the file
> disclaimer.txt.
> ;-
> ;----------------------------------------------------------- --
>
> function locmax, img, mask=m, where=w, ix=ix, iy=iy, sort=srt, $
> values=v, value_image=vimg, noedge=noed, help=hlp
>
> fuzz = 1.e-8 ; Ignore values below this.
>
> ;----- Shift four ways -----
> dx1 = shift(img,1,0)
> dx2 = shift(img,-1,0)
> dy1 = shift(img,0,1)
> dy2 = shift(img,0,-1)
> ;------ compare each pixel to 4 surrounding values -------
> m = (img gt dx1) and (img gt dx2) and (img gt dy1) and (img gt dy2)
> if keyword_set(noed) then imgfrm, m, 0
> ;------ number of local maxima --------
> w = where(m eq 1, count) ; Find local maxima.
> fzz = img(w) ; Pull out values.
> wfzz = where(fzz lt fuzz, c) ; Look for values below fuzz.
> if c gt 0 then begin ; Found any?
> m(w(wfzz)) = 0 ; Yes, zap them.
> w = where(m eq 1, count) ; Now try again for local maxima.
> endif
> ;------ if any continue ------
> if count gt 0 then begin
> if n_elements(vimg) eq 0 then begin ; Pick off values at maxima.
> v = img(w)
> endif else begin
> v = vimg(w)
> endelse
> if keyword_set(srt) then begin ; Sort?
> is= reverse(sort(v)) ; yes.
> v = v(is)
> w = w(is)
> endif
> one2two, w, img, ix, iy ; Convert to 2-d indices.
> endif
>
> return
>
> end
You'll need to use some of those keywords to get the results out
too...
-Jeremy.
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