% 裝載原始圖像
load belmont2; 
nbc = size(map,1);
% 使用coif2執(zhí)行3層小波包
wname = 'coif2'; lev = 3;
tree = wpdec2(X,lev,wname);
% 由第1層的h,v,d高頻系數(shù)估計(jì)噪聲的標(biāo)準(zhǔn)差
det1 = [wpcoef(tree,2) wpcoef(tree,3) wpcoef(tree,4)];
sigma = median(abs(det1(:)))/0.6745;
% 使用wpbmpen進(jìn)行全局閾值選擇
alpha = 1.1;
thr = wpbmpen(tree,sigma,alpha)
% 使用wpdencmp函數(shù)，采用上面的閾值和軟閾值處理方式，保存低頻，進(jìn)行圖像降噪
keepapp = 1;
xd = wpdencmp(tree,'s','nobest',thr,keepapp);
% 畫出原始圖像和降噪后的圖像
figure(2)
colormap(pink(nbc));
subplot(121), image(wcodemat(X,nbc))
title('原始圖像')
subplot(122), image(wcodemat(xd,nbc))
title('降噪后的圖像')