bisynt3.m

这是伯克里wavelet transforms一书中的例子的代码

function bsy = bisynt3(an,lpf,hpf)
%sy= bisynt3(sub,lpf,hpf) takes the one level 
%subband decomposed signal sub and reconstructs 
%the original signal using a synthesis filter bank
%defined by lpf and hpf. The filters are WSS and 
%the extensions are accordingly defined. The signal
%is odd length. The result is returned to array sy.
%The subbands are symmetrically extended.
%
%This routine is used by synthw for reconstruction of 
%wavelet decomposed sequences. 
%
%Author: Ajit S. Bopardikar
%Copyright (c) 1998 by Addison Wesley Longman, Inc.
%

  l  = length(an);
  ll = length(lpf);
  lh = length(hpf);
  le = (ll-1)/2;
  he = (lh-1)/2;

  %isolate the subbands

  if (le/2 == round(le/2)) %analysis lpf has odd group delay
    lo = an(1:floor(l/2));
    hi = an(floor(l/2)+1:l);
%upsample
    lu = zeros([1,l]);
    hu = zeros([1 l]);
    lu(2:2:l) = lo;
    hu(1:2:l) = hi;
    el = [lu(le+1:-1:2) lu lu(l-1:-1:max(1,l-le-1))]; %symmetric extension
    eh = [hu(he+1:-1:2) hu hu(l-1:-1:max(1,l-he-1))]; %symmetric extension
    r0 = conv(el,lpf);
    r1 = conv(eh,hpf);    
  elseif (he/2 == round(he/2)) %analysis lpf has even group delay
    lo = an(1:ceil(l/2));
    hi = an(ceil(l/2)+1:l);
%upsample
    lu = zeros([1,l]);
    hu = zeros([1 l]);
    lu(1:2:l) = lo;
    hu(2:2:l) = hi;
    el = [lu(le+1:-1:2) lu lu(l-1:-1:max(1,l-le-1))]; %symmetric extension
    eh = [hu(he+1:-1:2) hu hu(l-1:-1:max(1,l-he-1))]; %symmetric extension
    r0 = conv(el,lpf);
    r1 = conv(eh,hpf);
  end; %endif

   bsy = r0(ll:l+ll-1)+ r1(lh:l+lh-1);