[h, g, a, info] = wfilt_db(N, compat = 1);
N | Order of Daubechies filters. |
compat | 0 is precomputed LUT for \(N <= 38\), 1 is runtime calculation (default). |
H | cell array of analysing filters impulse reponses |
G | cell array of synthetizing filters impulse reponses |
a | array of subsampling (or hop) factors accociated with corresponding filters |
info | info.istight=1 indicates the wavelet system is a can. tight frame |
[H, G] = wfilt_db(N) computes a two-channel Daubechies FIR filterbank from prototype maximum-phase analysing lowpass filter obtained by spectral factorization of the Lagrange interpolator filter. N also denotes the number of zeros at \(z = -1\) of the lowpass filters of length \(2N\). The prototype lowpass filter has the following form (all roots of \(R(z)\) are inside of the unit circle):
where \(R(z)\) is a spectral factor of the Lagrange interpolator \(P(z) = 2 R(z) * R(z^{-1})\) All subsequent filters of the two-channel filterbank are derived as follows:
making them an orthogonal perfect-reconstruction QMF.
wfiltinfo('db8');
I. Daubechies. Ten Lectures on Wavelets. Society for Industrial and Applied Mathematics, Philadelphia, PA, USA, 1992.