"Approximation" and "detail " in wavelet

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Amani
Amani 2012-1-7
hello everyone ,
I use this function
wdencmp('gbl',C,L,'wname',N,THR,SORH,KEEPAPP)
as
[thr,sorh,keepapp] = ddencmp('den','wv',SourceSignal);
xd =wdencmp('gbl',SourceSignal,'sym8',8,thr,'h',keepapp);
and KEEPAPP is return 1
I search and found this:
If KEEPAPP = 1, approximation coefficients cannot be thresholded, otherwise it is possible.
Detail coefficient thresholding. For each level from 1 to N, a threshold is selected and hard thresholding is applied to the detail coefficients.
what are mean by (approximation) and (detail) ??

回答(1 个)

Wayne King
Wayne King 2012-1-7
The approximation, or scaling, coefficients are the lowpass representation of the signal and the details are the wavelet coefficients. At each subsequent level, the approximation coefficients are divided into a coarser approximation (lowpass) and highpass (detail) part.
Another way to state it is that the details are what is missing from the approximation at level J to get to the approximation at level J-1.
  1 个评论
Amani
Amani 2012-1-7
I am a Beginner in wavelet,
and i'm not understood this division depends on what ?
can you explain more ? .. please :(

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