%用原圖像與壓縮后的圖像相減
I = imread('cameraman.tif'); 
I = double(I)/255; 
%計算離散變換矩陣，返回結果為雙精度型
T = dctmtx(8); 
%實現(xiàn)圖像的顯示塊操作
B = blkproc(I,[8 8],'P1*x*P2',T,T'); 
mask =[1 1 1 1 0 0 0 0
      1 1 1 0 0 0 0 0
    1 1 0 0 0 0 0 0
      1 0 0 0 0 0 0 0
      0 0 0 0 0 0 0 0
      0 0 0 0 0 0 0 0
      0 0 0 0 0 0 0 0
  0 0 0 0 0 0 0 0];
B2 = blkproc(B,[8 8],'P1.*x',mask);
I2 = blkproc(B2,[8 8],'P1*x*P2',T',T);
imshow(I), figure, imshow(I2)
M=I2-I;
figure, imshow(mat2gray(M))