cl;
img_gray=imread('fupeng.jpg');
img_erzhi=imread('erzhi_fupeng.jpg');
imshow(img_gray)
figure,imshow(img_erzhi)
[m n]=size(img_gray);
img_gray_fu=zeros(m,n);
img_gray_peng=zeros(m,n);
img_erzhi_fu=zeros(m,n);
img_erzhi_peng=zeros(m,n);

for i=2:m-1
for j=2:n-1
        img_gray_fu(i,j)=min(min(img_gray(i-1:i+1,j-1:j+1)));
        img_gray_peng(i,j)=max(max(img_gray(i-1:i+1,j-1:j+1)));
end
end

figure,imshow(uint8(img_gray_fu));
figure,imshow(uint8(img_gray_peng));


for i=2:m-1
for j=2:n-1
        img_erzhi_fu(i,j)=min(min(img_erzhi(i-1:i+1,j-1:j+1)));
        img_erzhi_peng(i,j)=max(max(img_erzhi(i-1:i+1,j-1:j+1)));
end
end

figure,imshow(uint8(img_erzhi_fu));
figure,imshow(uint8(img_erzhi_peng));