How can i modiy this SNN filter code to handle color images? Also it takes much time. I got this over net. plz anybody suggest / improve this.

function [Y,Xpad] = snn12(X,WINSZ,true)
% [Y,Xpad] = SNN(X[,WINSZ][,progress])
% perform symmetric nearest-neighbor nonlinear edge-preserving filtering on 
% an intensity image
%
% * If no window size WINSZ is specified, the default is 5.
% * Setting progress to a nonzero value causes SSN to display
%   the current row it is processing.
%
% Description:
% The SNN filter works by looking at each pair of pixels opposite the
% output (center) pixel. From each pair, the one that is closest to
% the output pixel is used to compute the output (mean of all selected
% pixels).
% 
% Notes:
% Image is converted to double format for processing.
%
% Copyright Art Barnes, 2005 artbarnes<at>ieee<dot>org

if nargin >= 3
    verboseFlag = true;
else
    verboseFlag = false;
end

if nargin < 2
    WINSZ = 3;
end

if ~isa(X,'double')
    X = im2double(X);
end

PADDING = floor(WINSZ/2);

Xpad = padarray(X,[PADDING PADDING],'symmetric','pre');
[padRows,padCols] = size(Xpad);
Y = zeros(size(X));

nRowIters = length((PADDING+1):(padRows-PADDING));
count = 1;
for i = (PADDING+1):(padRows-PADDING)
    for j = (PADDING+1):(padCols-PADDING)

          % window 
          W = Xpad((i-PADDING):(i+PADDING),(j-PADDING):(j+PADDING));

          Wtop = W(1:PADDING,:)';
          Wtop = Wtop(:)';
          Wtop = [Wtop W(PADDING+1,1:PADDING)];
          Wbot = W((end-PADDING+1):end,:)';
          Wbot = Wbot(:)';
          Wbot = [W(PADDING+1,(end-PADDING+1):end) Wbot];     
          Wbot = fliplr(Wbot);

          NN = [Wtop; Wbot];
          NNdiff = abs(NN - W(PADDING+1,PADDING+1)); % or use X(i,j)
          [y,ids] = min(NNdiff);

          for k = 1:length(ids)
              NNnearest(k) = NN(ids(k),k);
          end

          Y(i,j) = mean([NNnearest Xpad(i,j)]);
      end

      %if verboseFlag & ~mod(count,10)
       %   fprintf('SNN: %d/%d\n',count,nRowIters);
      %end

      count = count + 1;
  end

Answer 1

[Image Analyst]

Just apply it to each color channel one at a time. If you get color artifacts from that, then convert to hsv space with rgb2hsv() and apply it to only the v channel, then get back to rgb with hsv2rgb(), which is probably a lot faster than the 3 color channel approach since you only call the filter twice, though you do have two color space conversions.

See attached demo. (I did not include the function in the file I uploaded because of the copyright mentioned.)

[D.Regan]

thanks. I already used rgb2ycbcr but got artifact in output.Now I'll try this your way.