nadia - if you want to extract every 31x31 block, then you could try using blockproc from the Image Processing Toolbox, or you could try the following (which should work though is not necessarily that efficient). Create a cell array for all of your distinct blocks as
blockSize = 31; % assumed square
imageSize = 512; % assumed square
blockArray = cell(imageSize - blockSize +1);
Now iterate over each 31x31 block as follows
for r=1:size(blockArray,1)
for c=1:size(blockArray,2)
blockArray{r,c} = myImage(r:r - 1 + blockSize, ...
c:c - 1 + blockSize);
end
end
where myImage is your 512x512 image. Note how we move the sliding window across each row r and column c.
