Find the boundaries of a local maxima - matlab

Question

I have a 2D image (matrix). I have found the local maxima of this image. Now I want to define the boundaries around each local maxima in such a way that I want all the pixels around the local maxima that have a value above 85% of the maximum.
Here is my existing code:
function [location]= Mfind_peak_2D( Image,varargin )
p = inputParser;
addParamValue(p,'max_n_loc_max',5);
addParamValue(p,'nb_size',3);
addParamValue(p,'thre',0);
addParamValue(p,'drop',0.15);
parse(p,varargin{:});
p=p.Results;
if sum(isnan(Image(:)))>0
Image(isnan(Image))=0;
end
hLocalMax = vision.LocalMaximaFinder;
hLocalMax.MaximumNumLocalMaxima = p.max_n_loc_max;
hLocalMax.NeighborhoodSize = [p.nb_size p.nb_size];
end

Answer 1

This should do the job (the code is full of comments and should be pretty self-explanatory but if you have doubts feel free to ask for more details):
% Load the image...
img = imread('peppers.png');
img = rgb2gray(img);
% Find the local maxima...
mask = ones(3);
mask(5) = 0;
img_dil = imdilate(img,mask);
lm = img > img_dil;
% Find the neighboring pixels of the local maxima...
img_size = size(img);
img_h = img_size(1);
img_w = img_size(2);
res = cell(sum(sum(lm)),3);
res_off = 1;
for i = 1:img_h
for j = 1:img_w
if (~lm(i,j))
continue;
end
value = img(i,j);
value_thr = value * 0.85;
% Retrieve the neighboring column and row offsets...
c = bsxfun(#plus,j,[-1 0 1 -1 1 -1 0 1]);
r = bsxfun(#plus,i,[-1 -1 -1 0 0 1 1 1]);
% Filter the invalid positions...
idx = (c > 0) & (c <= img_w) & (r > 0) & (r <= img_h);
% Transform the valid positions into linear indices...
idx = (((idx .* c) - 1) .* img_h) + (idx .* r);
idx = reshape(idx.',1,numel(idx));
idx = idx(idx > 0);
% Retrieve the neighbors and filter them based on te threshold...
neighbors = img(idx);
neighbors = neighbors(neighbors > value_thr);
% Update the final result...
res(res_off,:) = {sub2ind(img_size,i,j) value neighbors};
res_off = res_off + 1;
end
end
res = sortrows(res,1);
The variable res will be a cell matrix with three columns: the first one contain the linear indices to the local maxima of the image, the second one contains the values of the local maxima and the third one a vector with the pixels around the local maxima that fall within the specified threshold.