转载来自：http://blog.csdn.net/bluecol/article/details/46390105

%装载原始图像信号并图示 
X = imread('ddd.png') ;
subplot(2,2,1); 
image(mat2gray(X)); 
title('原始图像'); 
axis square; 
%============================== 
%生成含噪图像并图示 
init=2055615866; 
rand('seed',init); 
noise = 12*randn(size(X));
XX=uint8(double(X)+noise);
subplot(2,2); 
image(mat2gray(XX)); 
title('含噪图像'); 
axis square; 
%============================== 
%首先用sym4小波函数对XX进行2层分解 
[c,l]=wavedec2(XX,'sym4'); 
%实现低通滤波消噪 
a1=wrcoef2('a',c,l,'sym4',1); 
%再次实现低通滤波消噪 
a2=wrcoef2('a',2); 
%============================== 
%图示消噪处理后的结果 
subplot(2,3); 
image(mat2gray(a1)); 
title('第一次消噪图像'); 
axis square; 
subplot(2,4); 
image(a2); 
title('第二次消噪图像'); 
axis square;