how do i automatically select the kernel size like 5*5, 7*7... instead of the 3*3 in the code below

clc;
clear all;
close all;
es=imread('cameraman.Tif');
es=imnoise(es,'salt & pepper',0.5);
b=es;
[r,c]=size(es);
for i=2:r-1
    for j=2:c-1
        mat=[es(i-1,j-1),es(i-1,j),es(i-1,j+1),es(i,j-1),es(i,j),es(i,j+1),es(i+1,j-1),es(i+1,j),es(i+1,j+1)];
        mat=sort(mat);
        b(i,j)=mat(5);
    end
end
figure;     
imshow(es);
title('Image corrupted with Salt & Pepper Noise');
figure;
imshow(b);
title('Image after filtering');

[Walter Roberson]

What should the criteria be for deciding whether a 5*5 or 7*7 is better or more justified than a 3*3 ? What should the code be looking for in order to decide which size to use ?

Answer 1

[Rik]

This is a terrible way to write a median filter. Since the use of imnoise indicates that you already have the Image Processing toolbox, why not use medfilt2?

[Baththama Alhassan]

what i am asking of how to choose different window size not the median filte, so that with the knowledge I can use it in another algorithm.

[Rik]

Your code is applying a median filter with a 3*3 kernel. That makes it equivalent to this:

es=imread('cameraman.tif');
es=imnoise(es,'salt & pepper',0.5);
es = padarray(es,[1 1],0,'both');%add padding since your code doesn't filter the edges

isequal( b , medfilt2(es,[3 3]) )

ans = logical
   1

As you can see, this way it is trivial to change the kernel size to 5*5 or 7*7.

Why do you want to use your double loop?

Answer 2

[Walter Roberson]

window_size = randi([2 6]) * 2 - 1

window_size = 7

hws = (window_size - 1)/2;

es = imread('cameraman.tif');
assert(ndims(es) == 2, 'Grayscale images only!');

es = imnoise(es,'salt & pepper',0.5);
b = es;
[r,c]=size(es);
for i=1+hws:r-hws
    for j=1+hws:c-hws
        mat = es(i-hws:i+hws, j-hws:j+hws);
        mat = sort(mat(:));
        b(i,j)= mat((end-1)/2);
    end
end
figure;     
imshow(es);
title('Image corrupted with Salt & Pepper Noise');

figure;
imshow(b);
title( sprintf('Image after filtering window size %d', window_size) );