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Soum
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Denoising by Donoho algorithm

Asked by Soum
on 15 Jun 2013
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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1 Answer

Answer by Wayne King
on 15 Jun 2013
Edited by Wayne King
on 15 Jun 2013
 Accepted Answer

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;

  8 Comments

Soum
on 16 Jun 2013
THANK YOU AGAIN :) but you didn't understand me whatt does it mean the 't'??? NC = wthcoef2('t',C,S,1,thr,'s');
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
on 25 Jun 2013
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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