clear
clc

I = imread('lena.bmp');
Ilu = I(1:128, 1:128);
Iru = I(1:128, 129:256);
Ild = I(129:256, 1:128);
Ird = I(129:256, 129:256);

IluNoise = imnoise(Ilu,'salt & pepper', 0.05);
IruNoise = imnoise(Iru,'salt & pepper', 0.15);
IldNoise = imnoise(Ild,'salt & pepper', 0.25);
IrdNoise = imnoise(Ird,'salt & pepper', 0.50);

Inoise = [IluNoise IruNoise; IldNoise IrdNoise];

Imed3x3 = ordfilt2(Inoise, 5, ones(3));
Imed7x7 = ordfilt2(Inoise, 25, ones(7));
Imed11x11 = ordfilt2(Inoise, 61, ones(11));

subplot(2,3,1), imshow(I,[0 255]), title('Original')
subplot(2,3,2), imshow(Inoise,[0 255]), title('Noisy')
subplot(2,3,4), imshow(Imed3x3,[0 255]), title('Median filtered 3x3')
subplot(2,3,5), imshow(Imed7x7,[0 255]), title('Median filtered 7x7')
subplot(2,3,6), imshow(Imed11x11,[0 255]), title('Median filtered 11x11')