pkg load image
clear
clc

I = imread('lena.bmp');
Inoise = imnoise(I, 'salt & pepper', 0.05);

H5x5 = (1/25)*ones(5);
Ifiltered = imfilter(Inoise, H5x5);

psnr_orig_filt = psnr(I, Ifiltered, 255);

errorImage = abs(I - Ifiltered);

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(Ifiltered,[0 255]), title('Filtered')
subplot(2,3,5), imshow(errorImage,[]), title('Error image')
subplot(2,3,6), imhist(errorImage), axis([0 60 0 10000]), title('Error histogram')