用图像的块的极大值对图像进行处理

clc;
clear all;
close all;
img=imread('C:/lena.jpg');
[m n]=size(img);
I=zeros(m,n);
for i=2:m-1
    for j=2:n-1
%         sum=0;
%         for k=-1:1
%             for p=-1 :1
%                 sum=sum+I(i+k,j+p);
%             end
%         end
        I(i,j)=max(max(img(i-1:i+1,j-1:j+1)));
    end
end
 imshow(I,[])