pkg load image
clear
clc

I = imread('lena.bmp');

I2 = I;
I2N = imnoise(I2,'salt & pepper', 0.03);

Icentral = I(79:158, 79:158);
IcentralN = imnoise(Icentral,'salt & pepper', 0.30);

I2N(79:158, 79:158) = IcentralN;

H5x5 = (1/25) * ones(5);
HWA = (1/16) * [1 2 1; 2 4 2; 1 2 1];

I2N_AVG_5x5 = imfilter(I2N, H5x5);
I2N_WA_3x3 = imfilter(I2N, HWA);
I2N_MEDIAN_5x5 = ordfilt2(I2N, 5, ones(3));

pnsr_AVG = psnr(I2N_AVG_5x5, I, 255);
pnsr_WA = psnr(I2N_WA_3x3, I, 255);
pnsr_MED = psnr(I2N_MEDIAN_5x5, I, 255);
subplot(2,3,1), imshow(I,[0 255]), title('Original')
subplot(2,3,2), imshow(I2N,[0 255]), title('Noisy')
subplot(2,3,4), imshow(I2N_AVG_5x5,[0 255]), title('AVG filter')
subplot(2,3,5), imshow(I2N_WA_3x3,[0 255]), title('WA filter')
subplot(2,3,6), imshow(I2N_MEDIAN_5x5,[0 255]), title('Median filter')