Denoising by Donoho algorithm

Question

Soum 2013-6-15

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/79161-denoising-by-donoho-algorithm

Hello I'm trying to apply Donoho formula on my noisy image to get the threshold value and apply it on details coefficients which i get it by using wavedec function please someone help me to get a results if some one have another idea for make my code useful please just tell me I'm waiting

clear all

I=imread('cameraman.tif');

n = prod( size(I) );

I=double(I);

Ib=I+25*randn(size(I));% add noise

[C,S] = wavedec2(Ib,2,'bior3.7');

DH = detcoef2('all',C,S,1);% extract details coefficient from level 1

delta = median( abs(DH) ) / 0.6745;

thr = delta * sqrt(2*log(n));

NC = wthcoef2('bior3.7',C,S,DH,thr,s) % i use the soft threshold

X = waverec2(C, S, 'bior3.7'); % how can i get my image after threshold

figure(2)

imagesc(X);axis off;colormap(gray)

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Answer 1

Wayne King 2013-6-15

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https://ww2.mathworks.cn/matlabcentral/answers/79161-denoising-by-donoho-algorithm#answer_88882

编辑：Wayne King 2013-6-15

在 MATLAB Online 中打开

You want to use the thresholded coefficients in the reconstruction. You also made a couple other errors in your code.

    I = imread('cameraman.tif');
    n = prod( size(I) );
    I = double(I);
    Ib = I+25*randn(size(I));% add noise
    [C,S] = wavedec2(Ib,2,'bior3.7');
    DH = detcoef2('all',C,S,1);% extract details coefficient from level 1
    DH = DH(:);
    delta = median( abs(DH) ) / 0.6745;
    thr = delta * sqrt(2*log(n));
    NC = wthcoef2('t',C,S,1,thr,'s'); % i use the soft threshold
    X = waverec2(NC, S, 'bior3.7');
    figure;
    imagesc(Ib); title('Noisy Image'); colormap gray;
    figure;
    imagesc(X); title('Denoised 1st level coeffs'); colormap gray;

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Walter Roberson 2013-6-22

在 MATLAB Online 中打开

The 't' is a literal string. http://www.mathworks.com/help/wavelet/ref/wthcoef2.html

NC = wthcoef2('t',C,S,N,T,SORH) returns the detail coefficients obtained from the wavelet decomposition structure [C,S] by soft (if SORH ='s') or hard (if SORH ='h') thresholding (see wthresh for more information) defined in vectors N and T. N contains the detail levels to be thresholded and T the corresponding thresholds which are applied in the three detail orientations. N and T must be of the same length.

Soum 2013-6-25

Thanks Mr.Walter Yes I've read this http://www.mathworks.com/help/wavelet/ref/wthcoef2.html but my Problem is why we put the t ???? t is a literal string but what does it mean ?

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