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ptycho/utils/simple_nlm.m

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+function [output]=simple_nlm(input,t,f,h1,h2,selfsim)
+ 
+ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+ %
+ %  input   : image to be filtered
+ %  t       : radius of search window
+ %  f       : radius of similarity window
+ %  h1,h2   : w(i,j) = exp(-||GaussFilter(h1) .* (p(i) - p(j))||_2^2/h2^2)
+ %  selfsim : w(i,i) = selfsim, for all i
+ %
+ %  Note:
+ %    if selfsim = 0, then w(i,i) = max_{j neq i} w(i,j), for all i
+ %
+ %  Author: Christian Desrosiers
+ %  Date: 07-07-2015
+ %
+ %  Reimplementation of the Non-Local Means Filter by Jose Vicente Manjon-Herrera
+ %
+ %  For details see:
+ %     A. Buades, B. Coll and J.M. Morel, "A non-local algorithm for image denoising"
+ %
+ %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
+ 
+ [m, n]=size(input);
+ pixels = input(:);
+ 
+ s = m*n;
+ 
+ psize = 2*f+1;
+ nsize = 2*t+1;
+
+ % Compute patches
+ padInput = padarray(input,[f f],'symmetric'); 
+ filter = fspecial('gaussian',psize,h1);
+ patches = repmat(sqrt(filter(:))',[s 1]) .* im2col(padInput, [psize psize], 'sliding')';
+ 
+ % Compute list of edges (pixel pairs within the same search window)
+ indexes = reshape(1:s, m, n);
+ padIndexes = padarray(indexes, [t t]);
+ neighbors = im2col(padIndexes, [nsize, nsize], 'sliding');
+ TT = repmat(1:s, [nsize^2 1]);
+ edges = [TT(:) neighbors(:)];
+ RR = find(TT(:) >= neighbors(:));
+ edges(RR, :) = [];
+ 
+ % Compute weight matrix (using weighted Euclidean distance)
+ diff = patches(edges(:,1), :) - patches(edges(:,2), :);
+ V = exp(-sum(diff.*diff,2)/h2^2); 
+ W = sparse(edges(:,1), edges(:,2), V, s, s);
+ 
+ % Make matrix symetric and set diagonal elements
+ if selfsim > 0
+    W = W + W' + selfsim*speye(s);
+ else
+     maxv = max(W,[],2);
+     W = W + W' + spdiags(maxv, 0, s, s);
+ end     
+ 
+ % Normalize weights
+ W = spdiags(1./sum(W,2), 0, s, s)*W;
+ 
+ % Compute denoised image
+ output = W*pixels;
+ output = reshape(output, m , n);