daub.m

Double Density Wavelet Soft

function [h0, h1] = daub(K,str);
% [h0, h1] = daub(K);
% h0 : Daubechies lowpass filter
% h1 : Daubechies highpass filter
% K zeros at z=-1
% length = 2K
% Use [h0, h1] = daub(K,'mid') for mid-phase type

[h,s,g] = maxflatI(K,K-1);

r = roots(g);
r = r(abs(r) < 1);
q = real(poly(r));

if nargin > 1
	if strcmp(str,'mid')
		q = sfact_mid(g);
	end
end

q = q/sum(q);                 % normalize
h0 = q;                       % set  h0 = q;
for k = 1:K                   % make h0 = q * [(z^(-1)+1)/2]^K
   h0 = conv(h0,[1 1]/2);
end
h0 = sqrt(2)*h0;              % normalize so that sum(h0) = sqrt(2)

h1 = h0(end:-1:1);
h1(2:2:end) = -h1(2:2:end);