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)));    endend imshow(I,[])