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I have an image in MATLAB:
y = rgb2gray(imread('some_image_file.jpg')); and I want to do some processing on it:
pic = some_processing(y); and find the local maxima of the output. That is, all the points in y that are greater than all of their neighbors.
I can't seem to find a MATLAB function to do that nicely. The best I can come up with is:
[dim_y,dim_x]=size(pic); enlarged_pic=[zeros(1,dim_x+2); zeros(dim_y,1),pic,zeros(dim_y,1); zeros(1,dim_x+2)]; % now build a 3D array % each plane will be the enlarged picture % moved up,down,left or right, % to all the diagonals, or not at all [en_dim_y,en_dim_x]=size(enlarged_pic); three_d(:,:,1)=enlarged_pic; three_d(:,:,2)=[enlarged_pic(2:end,:);zeros(1,en_dim_x)]; three_d(:,:,3)=[zeros(1,en_dim_x);enlarged_pic(1:end-1,:)]; three_d(:,:,4)=[zeros(en_dim_y,1),enlarged_pic(:,1:end-1)]; three_d(:,:,5)=[enlarged_pic(:,2:end),zeros(en_dim_y,1)]; three_d(:,:,6)=[pic,zeros(dim_y,2);zeros(2,en_dim_x)]; three_d(:,:,7)=[zeros(2,en_dim_x);pic,zeros(dim_y,2)]; three_d(:,:,8)=[zeros(dim_y,2),pic;zeros(2,en_dim_x)]; three_d(:,:,9)=[zeros(2,en_dim_x);zeros(dim_y,2),pic]; And then see if the maximum along the 3rd dimension appears in the 1st layer (that is: three_d(:,:,1)):
(max_val, max_i) = max(three_d, 3); result = find(max_i == 1); Is there any more elegant way to do this? This seems like a bit of a kludge.
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M = max( A ) returns the maximum elements of an array. If A is a vector, then max(A) returns the maximum of A . If A is a matrix, then max(A) is a row vector containing the maximum value of each column of A .
Description. TF = islocalmax( A ) returns a logical array whose elements are 1 ( true ) when a local maximum is detected in the corresponding element of A . TF = islocalmax( A , dim ) specifies the dimension of A to operate along. For example, islocalmax(A,2) finds local maximum of each row of a matrix A .
In image processing, the usual definition of a local maximum is that a pixel is considered to be a local maximum if and only if it is greater than or equal to all of its immediate neighbors. There is a convenient and efficient way to find all the local maxima pixels by using image dilation.
total = bwarea( BW ) estimates the area of the objects in binary image BW . total is a scalar whose value corresponds roughly to the total number of on pixels in the image, but might not be exactly the same because different patterns of pixels are weighted differently.
bw = pic > imdilate(pic, [1 1 1; 1 0 1; 1 1 1]); If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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