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2014-04-28 16:34:17

•   function [B] = hw7_b(file_name, block_size)
  % EE 8541
  % HW 1 Problem #7b
  % Performs a median filter on gray image given by file_name。
    
  % Works on a block of of size block_size x block_size (3x3, 5x5, 9x9)。
  % We assume block_size is odd。
  A = imread(file_name);
  [m,n] = size(A);
  % We need to be able to apply median filter at the boundary pixels。
    
  % Assume the image has Neumann boundary conditions。
  % The easiest way to handle this is to set up a matrix A2 that has 
  % the original image A in the center and copies the adjacent
  % pixel value around the edges。
    
  k = floor(block_size/2);  % How far we need to extend border。
  A2 = zeros(m+2*k,n+2*k);
  A2(k+1:m+k,k+1:n+k) = A;   % Original image in center。
    
  % Extend border pixels。
  % Handle the 4 corners first。
  A2(1:k,1:k) = A(1,1);                  % Upper left corner。
  A2(1:k,n+k+1:n+2*k) = A(1,n);          % Upper right corner。
    
  A2(m+k+1:m+2*k,n+k+1:n+2*k) = A(m,n);  % Lower right corner。
  A2(m+k+1:m+2*k,1:k) = A(m,1);          % Lower left corner。
    
  % To handle the sides, we need to copy 1 row/column at a time。
  for i = 1:k
    A2(i,k+1:n+k) = A(1,1:n);            % Upper。
    
    A2(k+1:m+k,n+k+i) = A(1:m,n);        % Right。
    A2(m+k+i,k+1:n+k) = A(m,1:n);        % Lower。
    A2(k+1:m+k,i) = A(1:m,1);            % Left。
    
  end;
  % Apply median filter to form matrix B。
  B=zeros(m,n);
  pixel_block = zeros(1,block_size^2);
  for i = 1:m
    for j = 1:n
          % Determine pixel block。
    
          k = floor(block_size/2);
          pixel_block = reshape(A2(i:i+2*k,j:j+2*k),block_size^2,1);
          
          % Find median without using median function。
    
          sorted_block = sort(pixel_block);
          median_position = ceil(block_size^2 / 2); 
          block_median = sorted_block (median_position);
   
          B(i,j) = block_median;
    end;
  end;
  B = uint8(B);   % For drawing purposes。
    

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  2014-04-28 16:34:17

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