Adaptive median filter

2 min readDec 6, 2021

clc;

clear all;
close all;
a=imread('cameraman.tif');
figure(1),imshow(a),title('origanal image');
b=imnoise(a,'salt & pepper',.02)
figure(2),imshow(b),title('noisy image');
Smax=9;for i=1:254
    for j=1:254
        n=b(i:i+2,j:j+2)
        Zmin=min(n(:));
        Zmax=max(n(:));
        Zmed=median(n(:));
        sx=3;
        sy=3;                A1=Zmed-Zmin;
                A2=Zmed-Zmax;
              if (A1>0) && (A2<0)
                  B1 = Zxy-Zmin;                  B2 = Zxy-Zmax;
                  if (B1>0) && (B2<0)
                        b(i:i+2,j:j+2) = n(i, j);
                      break;
                  else
                       b(i:i+2,j:j+2) = Zmed;
                      break;
                  end 
              else 
                  sx=sx+2;
                  sy=sy+2;
                  if (sx > Smax) && (sy > Smax)
                      b(i:i+2,j:j+2) = n(i, j);
                  end 
                  end 
      end 
      end figure(3),imshow(b),title('denoised image');

i am trying to implement the following algorithm but where the above pro. is wrong i am unable to find ..

please help me…….

Adaptive median filter changes size of Sxy (the size of the neighborhood) during operation.

? Notation
  Zmin = minimum gray level value in Sxy
  Zmax = maximum gray level value in Sxy
  Zmed = median of gray levels in Sxy
  Zxy = gray level at coordinates (x, y)
  Smax = maximum allowed size of Sxy? Algorithm
Level A: A1 = Zmed - Zmin
          A2 = Zmed - Zmax
          if A1 > 0 AND A2 < 0, go to level B
else increase the window size
if window size < Smax, repeat level A
else output Zxy
Level B: B1 = Zxy - Zmin
B2 = Zxy - Zmax
if B1 > 0 AND B2 < 0, output Zxy
else output Zmed

NOTE:-

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You need to take the contents of the “if” block and make it a function that takes the center location and the window size as input arguments. Then in the “else” block you need to increase the window size and call the function. Something like

% Determine window size.
if (A1>0) && (A2<0)
  windowSize = standardSize; % 3 or whatever

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