kk=imread('ziji4.jpg');
X=rgb2gray(kk);
X=double(X);

[c,s]=wavedec2(X,2,'sym4');
a0=waverec2(c,s,'sym4');
ans=max(max(abs(X-a0)))
 
 figure(4);
  subplot(121);
 imshow(X,[]);
title('原始圖像');
subplot(122);
imshow(a0,[]);
title('重構圖像');