Wavelet transform --dwt2 and wavedec2

https://www.cnblogs.com/xfzhang/p/7295041.html

https://www.ilovematlab.cn/thread-45020-1-1.html

dwt2 It's a two-dimensional single scale wavelet transform , It can decompose two-dimensional single scale wavelet by specifying wavelet or decomposition filter . and wavedec2 It is two-dimensional multiscale wavelet decomposition .

Scale can be understood as grade , namely wavedec2 It can be used for multilevel wavelet decomposition

dwt2:    [cA,cH,cV,cD]=dwt2(X,'wname');

wavedec2:   [C,S]=wavedec2(X,N,'wname'), among N For more than 1 The positive integer .

in other words dwt2 Only one input matrix X Perform a decomposition , and wavedec2 You can input matrix X Conduct N Second decomposition .

 

appcoef2： Extraction of low-frequency coefficients of two-dimensional discrete wavelet transform

  A = appcoef2(C,S,'wname',N)

  A = appcoef2(C,S,'wname')

  A = appcoef2(C,S,Lo_R,Hi_R)

  A = appcoef2(C,S,Lo_R,Hi_R,N)

 

   detcoef2： Extraction of high-frequency partial coefficients of two-dimensional discrete wavelet transform

cH1 Means level cV1 It means vertical  cD1 Represents diagonal   N Represent series

  [cH1,cV1,cD1] = detcoef2('all',C,S,N)

 

appcodef2 And detcoef2 difference ：

app It's approximate , That is, the low-frequency part of the signal ,dec It's details , That is, the high-frequency part of the signal ,
appcoef(s) It's a signal s The low frequency coefficient of
deccoef(s) Is the high frequency coefficient of the signal