自适应中值滤波算法的Matlab实现

本文程序来自冈萨雷斯数字图像处理Matlab中文版附录C

相对原文程序，（1）将第8行的‘|’更改为‘||’（2）第11行注释。其余保持不变。

%自适应中值滤波
function f = adpmedian (g, Smax)
% ADPMEDIAN Parform adaptive median filtering.
%   F = ADPMEDIAN(G, SMAX) performs adaptive median filtering of
%   image G. The median filter starts at size 3-by-3 and iterates up
%   to size SMAX-by-SMAX. SMAX must be an odd integer greater than 1.
% SMAX must be an odd, positive integer greater than 1.
if (Smax <= 1) || (Smax/2 == round(Smax/2)) || (Smax ~= round(Smax))
    error ('SMAX must be an odd integer > 1.')
end
% [M, N] = size(g);
% Initial setup.
f = g;
f(:) = 0;
alreadyProcessed = false (size(g));
% Begin filtering.
for k = 3:2:Smax
    zmin = ordfilt2(g, 1, ones(k, k),'symmetric');
    zmax = ordfilt2(g, k * k, ones(k, k), 'symmetric');
    zmed = medfilt2(g, [k k], 'symmetric');
    processUsingLevelB  = (zmed > zmin) & (zmax > zmed) &...
        ~alreadyProcessed;
    zB = (g > zmin) & (zmax > g);
    outputZxy = processUsingLevelB & zB;
    outputZmed = processUsingLevelB & ~zB;
    f (outputZxy) = g(outputZxy);
    f (outputZmed) = zmed(outputZmed);
    alreadyProcessed = alreadyProcessed | processUsingLevelB;
    if all (alreadyProcessed (:))
        break;
    end
end
% Output zmed for any remaining unprocessed pixels. Note that this
% zmed was computed using a window of size Smax-by-Smax, which is
% the final value of k in the loop.
f (~alreadyProcessed) = zmed (~alreadyProcessed);
end

使用方法： f = adpmedian (g, Smax)

其中：g为输入二维图像，Smax为最大滤波尺寸，f为自适应滤波后输出图像

参考实例：

Gray = imread('cameraman.tif'); %读取图像文件

%加入各种浓度的椒盐噪声
N1 = imnoise(Gray,'salt & pepper',0.05);%椒盐噪声，噪声密度0.05
N2 = imnoise(Gray,'salt & pepper',0.25);%椒盐噪声，噪声密度0.25
N3 = imnoise(Gray,'salt & pepper',0.45);%椒盐噪声，噪声密度0.45
N4 = imnoise(Gray,'salt & pepper',0.65);%椒盐噪声，噪声密度0.65

%中值滤波
M1 = medfilt2(N1);
M2 = medfilt2(N2);
M3 = medfilt2(N3);
M4 = medfilt2(N4);

%自适应中值滤波
f1 = adpmedian(N1,11);
f2 = adpmedian(N2,11);
f3 = adpmedian(N3,11);
f4 = adpmedian(N4,11);

figure
subplot(341);
imshow(N1);
subplot(342);
imshow(N2);
subplot(343);
imshow(N3);
subplot(344);
imshow(N4);

subplot(345);
imshow(M1);
subplot(346);
imshow(M2);
subplot(347);
imshow(M3);
subplot(348);
imshow(M4);

subplot(349);
imshow(f1);
subplot(3,4,10);
imshow(f2);
subplot(3,4,11);
imshow(f3);
subplot(3,4,12);
imshow(f4);

实验效果如下：

第一行分别为加入浓度0.05、0.25、0.45、0.65的椒盐噪声

第二行为中值滤波medfilt2处理效果，默认滤波尺寸 3*3

第三行为自适应中值滤波adpmedian 处理效果，最大滤波尺寸为11*11