matlab 自適應中值濾波程序 adpmedian.m

 來自岡薩雷斯數字圖像處理Matlab中文版附錄C

相對原文程序，（1）將第8行的‘|’更改爲‘||’（2）第11行註釋。其餘保持不變。

%自適應中值濾波
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爲輸入二維圖像，Smax爲最大濾波尺寸，f爲自適應濾波後輸出圖像

參考實例：

Gray = imread('cameraman.tif'); %讀取圖像文件

%加入各種濃度的椒鹽噪聲
N1 = imnoise(Gray,'salt & pepper',0.05);%椒鹽噪聲，噪聲密度0.05
N2 = imnoise(Gray,'salt & pepper',0.25);%椒鹽噪聲，噪聲密度0.25
N3 = imnoise(Gray,'salt & pepper',0.45);%椒鹽噪聲，噪聲密度0.45
N4 = imnoise(Gray,'salt & pepper',0.65);%椒鹽噪聲，噪聲密度0.65

%中值濾波
M1 = medfilt2(N1);
M2 = medfilt2(N2);
M3 = medfilt2(N3);
M4 = medfilt2(N4);

%自適應中值濾波
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);

實驗效果如下：

第一行分別爲加入濃度0.05、0.25、0.45、0.65的椒鹽噪聲

第二行爲中值濾波medfilt2處理效果，默認濾波尺寸 3*3

第三行爲自適應中值濾波adpmedian 處理效果，最大濾波尺寸爲11*11