f=imread('C:\Documents and Settings\lishurui\桌面\lena.bmp');
load lena;
subplot(2,2,1);image(X);colormap(map);
title('原始圖像');
axis square;
[c,s]=wavedec2(X,2,'sym4');
sizec=size(c);
for i=1;sizec(2)
    if(c(i)>350)
        c(i)=2*c(i);
    else 
        c(i)=0.5*c(i);
    end
end 
xx=waverec2(c,s,'sym4');
subplot(2,2,2);image(xx);
title('增強(qiáng)圖像')