pkg load image

clear
clc

I = imread('peppers.bmp');

Iup = I(1:128,:);
Idown = I(129:256,:);

IupNoise = imnoise(Iup, 'salt & pepper', 0.05);
IdownNoise = imnoise(Idown, 'salt & pepper', 0.25);

Inoise = [IupNoise; IdownNoise];

Havg = (1/25)*ones(5);
Hwa = (1/16)*[1 2 1; 2 4 2; 1 2 1];

ImedFilt = ordfilt2(Inoise,13,ones(5));
IavgFilt = imfilter(Inoise,Havg);
IwaFilt = imfilter(Inoise,Hwa);

psnrMED = psnr(ImedFilt,I,255);
psnrAVG = psnr(IavgFilt,I,255);
psnrWA = psnr(IwaFilt,I,255);

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(ImedFilt,[0 255]), title('5x5 median filtered')
subplot(2,3,5), imshow(IavgFilt,[0 255]), title('5x5 average filtered')
subplot(2,3,6), imshow(IwaFilt,[0 255]), title('3x3 weighted average filtered')