Check if nxm block of 1s is inside binary matrix

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Andrew Poissant 2018-10-5

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https://ww2.mathworks.cn/matlabcentral/answers/422364-check-if-nxm-block-of-1s-is-inside-binary-matrix

编辑： Bruno Luong 2018-10-5

MM_bin.mat

I have a 90x89 binary matrix (see attached). In short, the 1s are good and 0s are bad. I want a quick way to check and return any nxm blocks of all 1s within the large matrix. For example, I want to find out if there are any 3x6 (n=3, m=6) blocks of all 1s within the binary matrix. If there are, return the row and col for each cell within each block.

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Answer 1

Bruno Luong 2018-10-5

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https://ww2.mathworks.cn/matlabcentral/answers/422364-check-if-nxm-block-of-1s-is-inside-binary-matrix#answer_339931

编辑：Bruno Luong 2018-10-5

在 MATLAB Online 中打开

[i,j] = find(conv2(MM_bin,ones(3,6),'same')==3*6);

I was testing with MM_bin in your MATFILE file which is an 2D array (a matrix in short) that contains 0/1.

If you test on other array with more dimensions than 2, then it's normal that you get error.

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Andrew Poissant 2018-10-5

I am looking at it but the sub block of 1s is 3x6, so the "center" provided by the convolution isn't actually a centroid because it has an even number of points in one direction.

Bruno Luong 2018-10-5

编辑：Bruno Luong 2018-10-5

在 MATLAB Online 中打开

Yes the return index is shifted by half index for even size.

To compensate, dimension indexes of the box is (so single (i,j) pair)

wi = 3;
di = (wi-1)/2;
ibox = ceil(i-di) : ceil(i+di);
wj = 6;
dj = (wj-1)/2;
jbox = ceil(j-dj) : ceil(j+dj);
% MM_bin(ibox,jbox) == ones(3,6);

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Answer 2

Bruno Luong 2018-10-5

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https://ww2.mathworks.cn/matlabcentral/answers/422364-check-if-nxm-block-of-1s-is-inside-binary-matrix#answer_339925

编辑：Bruno Luong 2018-10-5

在 MATLAB Online 中打开

[i,j] = find(conv2(MM_bin,ones(3,6),'same')==3*6);

will return you all the positions (i,j) with 3*6 submatrix of ones centered at this position.

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Andrew Poissant 2018-10-5

在 MATLAB Online 中打开

Thank you for your answer. I get the following error:

Error using conv2
N-D arrays are not supported.
Error in FM5_LowBattery_newLZ (line 197)
[ii,jj] = find(conv2(MM_bin_land_windowed,ones(3,6),'same')==3*6);