afb_sym.m

来自「Double Density Wavelet Soft」· M 代码 · 共 44 行

function [lo, bp, hi] = afb_sym(x, af)

% ANALYSIS FILTER BANK
%    with symmetric extensions
%    for even-length h0, h1
% [lo, bp, hi] = afb_even(x, af)
% INPUT
%   x  : input signal (even-length)
%   af : analysis filters
% OUTPUT
%   lo : lowpass subband signal
%   bp : bandpass subband signal
%   hi : highpass subband signal

h0 = af{1};
h1 = af{2};
h2 = af{3};

N = length(x);              % length of input signal

% lowpass subband
L = length(h0);
A = L/2;
k = 0:A-1;
xe = [x(A-k) x x(N-k)];     % symmetric extension
lo = conv(xe, h0);          % filter
lo = lo(L+[1:2:N]);         % downsample

% bandpass subband
L = length(h1);
A = L/2;
k = 0:A-1;
xe = [x(A-k) x x(N-k)];     % symmetric extension
bp = conv(xe, h1);          % filter
bp = bp(L+[0:2:N]);         % downsample

% highpass subband
L = length(h2);
A = (L+1)/2;
k = 0:A-1;
xe = [x(A-k) x x(N-k)];     % symmetric extension
hi = conv(xe, h2);          % filter
hi = hi(L+[1:N]);           % downsample