Question about wavelet and reconstruction

5 ビュー (過去 30 日間)
tanglaoya
tanglaoya 2016 年 9 月 20 日
コメント済み: tanglaoya 2016 年 10 月 6 日
Dear all, I am studying wavelet and focusing on the signal reconstruction. I noticed that the function 'upcoef' just work for the reconstruction: http://cn.mathworks.com/help/wavelet/ref/upcoef.html
At the end of this page, I also noticed that upcoef is equivalent to an N time repeated use of the inverse wavelet transform.
Then I tried to test it with the following code:
t=0:2*pi/999:2*pi;
b0=sin(t);
figure,plot(b0);
[cA,cD]=dwt(b0,'db4',3);
D = upcoef('d',cD,'db4',3,length(b0));
figure,plot(D);
[cA,cD]=dwt(b0,'db4');
[cA,cD]=dwt(cA,'db4');
[cA,cD]=dwt(cA,'db4');
D=idwt([],cD,'db4');
D=idwt([],D,'db4');
D=idwt([],D,'db4',length(b0));
figure,plot(D)
However, results by two methods are different. Could anyone tell me what's wrong in the code?
Thanks, Tang Laoya
  3 件のコメント
tanglaoya
tanglaoya 2016 年 9 月 20 日
I changed code to the following:
t=0:2*pi/999:2*pi;
b0=sin(t);
figure,plot(b0);
[C,L]=wavedec(b0,3,'db4');
CA3=C(1:L(1));
CD3=C(L(1)+1:L(1)+L(2));
CD2=C(L(1)+L(2)+1:L(1)+L(2)+L(3));
CD1=C(L(1)+L(2)+L(3)+1:L(1)+L(2)+L(3)+L(4));
CD0 = upcoef('d',CD3,'db4',3,length(b0));
figure,plot(CD0);
%
[cA1,cD1]=dwt(b0,'db4');
[cA2,cD2]=dwt(cA1,'db4');
[cA3,cD3]=dwt(cA2,'db4');
D=idwt([],cD3,'db4');
D=idwt([],D,'db4');
cD0=idwt([],D,'db4',length(b0));
figure,plot(cD0)
errcA3=max(abs(CA3-cA3));
errCD3=max(abs(CD3-cD3));
errCD2=max(abs(CD2-cD2));
errCD1=max(abs(CD1-cD1));
errD=max(abs(CD0-cD0));
but results are still different.
tanglaoya
tanglaoya 2016 年 9 月 20 日
Not only the roundoff error. I guess there is something wrong in the code. Thanks

サインインしてコメントする。

回答 (1 件)

Wayne King
Wayne King 2016 年 10 月 4 日
One problem you are having is that DWT does not take the 3 input you are using. DWT only does a single-level wavelet transform unlike wavedec. The 3 input to DWT above is NOT being used. It has no effect on the output.
  1 件のコメント
tanglaoya
tanglaoya 2016 年 10 月 6 日
Hi Wayne, Thanks for your kindly reply. I did use wavedec in my latter comment, but the results are the same.

サインインしてコメントする。

カテゴリ

Help Center および File ExchangeDiscrete Multiresolution Analysis についてさらに検索

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by