1 files changed, 27 insertions, 0 deletions

diff --git a/MATLAB/boxfilter.m b/MATLAB/boxfilter.m
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+function imDst = boxfilter(imSrc, r)

+

+%   BOXFILTER   O(1) time box filtering using cumulative sum

+%

+%   - Definition imDst(x, y)=sum(sum(imSrc(x-r:x+r,y-r:y+r)));

+%   - Running time independent of r; 

+%   - Equivalent to the function: colfilt(imSrc, [2*r+1, 2*r+1], 'sliding', @sum);

+%   - But much faster.

+

+[hei, wid] = size(imSrc);

+imDst = zeros(size(imSrc));

+

+%cumulative sum over Y axis

+imCum = cumsum(imSrc, 1);

+%difference over Y axis

+imDst(1:r+1, :) = imCum(1+r:2*r+1, :);

+imDst(r+2:hei-r, :) = imCum(2*r+2:hei, :) - imCum(1:hei-2*r-1, :);

+imDst(hei-r+1:hei, :) = repmat(imCum(hei, :), [r, 1]) - imCum(hei-2*r:hei-r-1, :);

+

+%cumulative sum over X axis

+imCum = cumsum(imDst, 2);

+%difference over Y axis

+imDst(:, 1:r+1) = imCum(:, 1+r:2*r+1);

+imDst(:, r+2:wid-r) = imCum(:, 2*r+2:wid) - imCum(:, 1:wid-2*r-1);

+imDst(:, wid-r+1:wid) = repmat(imCum(:, wid), [1, r]) - imCum(:, wid-2*r:wid-r-1);

+end

+