Matlab代碼：

I= imread('1.jpg');%自己任意給出一張圖片

I=im2double(I);

H=rgb2gray(I);

J=imnoise(H, 'salt& pepper', 0.02);

h1=fspecial('average',3);

h2=fspecial('average',5);

h3=fspecial('average',7);

K1=filter2(h1, J);

K2=filter2(h2, J);

K3=filter2(h3, J);

subplot(221);imshow(J);title('0');

subplot(222);imshow(K1);title('1');

subplot(223);imshow(K2);title('2');

subplot(224);imshow(K3);title('3');

[g w]=size(K1);

L=imresize(K1,[floor(g/2)floor(w/2)]);

L=imresize(L,[gw]);

M=im2uint8(K1);

N=im2uint8(L);

B=8;

MAX=2^B-1;

MES=sum(sum((M-N).^2))/(g*w);

PSNR=20*log10(MAX/sqrt(MES))

[g w]=size(K2);

L=imresize(K2,[floor(g/2)floor(w/2)]);

L=imresize(L,[gw]);

M=im2uint8(K2);

N=im2uint8(L);

B=8;

MAX1=2^B-1;

MES1=sum(sum((M-N).^2))/(g*w);

PSNR1=20*log10(MAX1/sqrt(MES1))

[g w]=size(K3);

L=imresize(K3,[floor(g/2)floor(w/2)]);

L=imresize(L,[gw]);

M=im2uint8(K3);

N=im2uint8(L);

B=8;

MAX2=2^B-1;

MES2=sum(sum((M-N).^2))/(g*w);

PSNR2=20*log10(MAX2)/sqrt(MES2)