"Approximation" and "detail " in wavelet

Question

Amani 2012-1-7

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/25554-approximation-and-detail-in-wavelet

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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) ??

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Answer 1

Wayne King 2012-1-7

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https://ww2.mathworks.cn/matlabcentral/answers/25554-approximation-and-detail-in-wavelet#answer_33493

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.