www.pudn.com > guided-filter-code-v1.rar > boxfilter.m, change:2010-07-08,size:931b


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