Check if nxm block of 1s is inside binary matrix

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.

Answer 1

[Bruno Luong]

[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.

[Andrew Poissant]

Woops! I forgot that there are 2 other unimportant layers for this problem. So the answer only returns a single [i,j] pair. You said that is the center point of the block of 1s I am looking for? How do I extract all of the coordinates for the block that was found and what if there are multiple blocks within the larger matrix?

[Bruno Luong]

let as exercise

[Andrew Poissant]

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]

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);

Answer 2

[Bruno Luong]

[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.

[Andrew Poissant]

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);