how to locate group of pixels in a large image

suppose i have a group of pixels arranged as

28 29 30 31

30 31 32 30

34 34 33 32

34 34 35 34

which has been cropped from a larger image.

Is there away to locate and find the exact group of pixels given above in the larger image?

I have cropped this particular set of pixels from a large image few months ago. My system got crashed and I dont remember the locations of these set of data.

Thanks! :)

Answer 1

[neil jerome]

%% find known submatrix in large matrix
% will find all instances

sourceMat = magic(15); % example source matrix
targMat = [218 10 27; 9 26 43]; % example target submatrix
[s1, s2] = size(targMat); % size of target

searchGrid = zeros(size(sourceMat,1)-s1, size(sourceMat,2)-s2); % grid of possible locations

for ii = 1:size(sourceMat,1)-s1 % loop over first dimension
    for jj = 1:size(sourceMat,2)-s2 % loop over second dimension
       subMat =  sourceMat(ii:ii+s1-1,jj:jj+s2-1); % look at this region in source
       diff = sum(squash(subMat - targMat)); % compare target to this region
        if diff == 0 % is this region the same as target?
            searchGrid(ii,jj) = 1; % record success!
        end
    end
end

[rows, cols] = find(searchGrid); % coordinate pairs of top corner of matching areas
horzcat(rows, cols)

[Image Analyst]

You can use isequal:

      % Not needed : diff = sum(squash(subMat - targMat)); % compare target to this region
      % Compare current window with template using isequal().
      if isequal(subMat, targMat) % is this region the same as target?

[neil jerome]

yep :)