From 2c425c06f30ac4be6b0b6d35aab6d390b169efa4 Mon Sep 17 00:00:00 2001
From: Jinwei Zhao <clarkzjw@gmail.com>
Date: Thu, 21 Jan 2016 19:53:38 +0800
Subject: add MATLAB code

---
 MATLAB/boxfilter.m | 27 +++++++++++++++++++++++++++
 1 file changed, 27 insertions(+)
 create mode 100755 MATLAB/boxfilter.m

(limited to 'MATLAB/boxfilter.m')

diff --git a/MATLAB/boxfilter.m b/MATLAB/boxfilter.m
new file mode 100755
index 0000000..9990fa6
--- /dev/null
+++ b/MATLAB/boxfilter.m
@@ -0,0 +1,27 @@
+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
+
-- 
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