### Highlights from local maxima \ minima

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# local maxima \ minima

01 Apr 2007 (Updated )

a simple (but effective) code to find local maximas

File Information
Description

This is a very simple function to find the local maximum in any dimensional array. As simple as it is it still gives nice results.

I use the imdilate() function as a maximum operation and then compare the data to the result.

the data, a vector defining the minimum distance between peaks in each of the data dimensions. and a flag either to exclude equal points or not.

use examples:
a = cumsum(randn(1000,1));
peaks = localMaximum(a,[100]);
figure; plot(a); hold on; plot(peaks,a(peaks),'ro');

[x y] = meshgrid(-6:0.1:6,-6:0.1:6);
a = sinc(x).*sinc(y);
lMaxInd = localmaximum(a,[20 20]);
lMinInd = localMaximum(-a,[20 20]);
figure; mesh(x,y,a); hold on;
plot3(x(lMaxInd),y(lMaxInd),a(lMaxInd),'k*','markersize',10,'linewidth',1.5);
plot3(x(lMinInd),y(lMinInd),a(lMinInd),'g*','markersize',10','linewidth',1.5);
legend('sinc(x)sinc(y)','peaks','valleys','location','best')

P.S
- It is recommended to run (if possible) a LPF on the data before searching for the peaks

Required Products Image Processing Toolbox
MATLAB release MATLAB 7.0.4 (R14SP2)
19 Jul 2013
05 Mar 2013
01 Feb 2013

Thank you very much. this code is very helpful in find maxima in the matrices.

12 Sep 2012

very nice implementation of gray scale dilation to find max

21 May 2012
13 Dec 2011
21 Jul 2011
11 Nov 2009

good code :)

20 Mar 2009

Yonathan.

Nice, clean implementation. I'm a real fan of how concise this is - doing a similar thing without an image dilation makes for some really clunky code.

Shame that it includes the dependency on the image processing toolbox; I haven't found any freeware routines which do image dilation and could be used as a swap-out for imdilate. I'll let you know if I come across any.

The documentation could be a bit clearer (an explanation of what's going on fundamentally would be good, as someone who doesn't know about image dilation would probably avoid it); but it's plenty to get someone up and running the code.

Cheers!

Tom

03 Mar 2009

Good job, thanks you !
Without saying details, i use your code to get the second minima in experimentaly acquired data. That saves me time. I add that the function is very simple to use.
Cheers !

24 Sep 2008

Great code!
I prefered to exclude zerovalues in the input too!
first saving the original x
...
xold=x;
% exculdeEqualPoints
...
x = x + rand(size(x))*minimumDiff;
...
se = ones(minDist);
X = imdilate(x,se);
f = find(x == X & xold~=0);
...

16 Aug 2007

Good code, except it can catch all points on a rising edge (positive slope). If you fliplr the vector, run the algorithm in both directions and only accept points that fall in both solution bins, you get a much cleaner result. I'll try to post the code.

16 Apr 2007

Yonathan,

Thanks for updating your submission. It is indeed an interesting and effective use of the imdilate function.

05 Apr 2007

Dear Ken,
Well I sew so many methods posted for local maximum all are very complicated and usually give worst results then this simple method (numeric derivation tends to be noisy).

As the guy in the newsgroup was very pleased from this simple solution I thought it might interest others.

Error checking isn't exactly algorithm worth uploading (each one can do his won..)

And finally: IMHO nothing is more important then a catchy heading !

Still thanks for the comment :)

05 Apr 2007

The author posted this code in response to a question on the matlab newsgroup a few days ago. Basic error checking and meaningful help text are preferred over a "catchy heading."

02 Apr 2007

Two lines, and two filename clashes! 100%! ;)

16 Apr 2007

reasons for changes: nasty comments I got :)

I made the function a bit more user friendly. Instead of passing a "structure element" you pass to the function a number defining the minimum distance between two peaks.

18 Apr 2007

small improvements in the validity checks

25 May 2007

I added support of subscript and index according to the nargout

20 Sep 2007

I added an option to exclude plateau points - I do it by adding noise which won't affect the real peaks position. As it is rather heavy you might not want to use this (default option is off).