Can someone please help me implementing this code without loop ?

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pb1106 2018-11-4

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重新打开： pb1106 2018-11-5

采纳的回答： Bruno Luong

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Hello,

Can someone help me to speed up this code? Without loops

img = imread("my_img.png");
for i=2:256
    for j=2:256
        v1(i,j) = max(abs(img(i+1,j)-img(i,j)),abs(img(i-1,j)-img(i,j)));
        v2(i,j) = max(abs(img(i,j-1)-img(i,j)),abs(img(i,j+1)-img(i,j)));
        v3(i,j) = max(abs(img(i-1,j+1)-img(i,j)),abs(img(i+1,j-1)-img(i,j)));
        v4(i,j) = max(abs(img(i+1,j+1)-img(i,j)),abs(img(i-1,j-1)-img(i,j)));
    end
end
min_v1 = min(v1);
min_v2 = min(v2);
min_v3 = min(v3);
min_v4 = min(v4);

Thanks

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Bruno Luong 2018-11-4

编辑：Bruno Luong 2018-11-4

Preallocation or not it's still give outcome vectors containing only 0s.

At this point I'm not even sure the formula inside the for-loop is really what you want, since there are still errors somewhere else after 2/3 corrections.

I suggest you debug your code and post the version that works as you expected, then ask the question because we can't help you to remove a loop if we don't know what is the expected result.

pb1106 2018-11-4

编辑：pb1106 2018-11-4

This is what I'm trying to implement

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采纳的回答

Bruno Luong 2018-11-4

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f = rand(4,5);
[m,n] = size(f);
x = 2:m-1;
y = 2:n-1;
v1 = max(abs(f(x+1,y)-f(x,y)),abs(f(x-1,y)-f(x,y)));
v2 = max(abs(f(x,y-1)-f(x,y)),abs(f(x,y+1)-f(x,y)));
v3 = max(abs(f(x-1,y+1)-f(x,y)),abs(f(x+1,y-1)-f(x,y)));
v4 = max(abs(f(x+1,y+1)-f(x,y)),abs(f(x-1,y-1)-f(x,y)));
vmin = min(cat(3,v1,v2,v3,v4),[],3);
alpha = 0.1;
[x,y] = find(vmin>alpha);
x = x+1;
y = y+1;
I_f = [x y]