idd2.m

多小波分析工具箱

function x=idd2(Y)
%IDD2 Single-level inverse discrete 2-D wavelet transform.
%   IDD2 performs a single-level inverse 2-D wavelet reconstruction
%   using Daubechies wavelet with four coefficients
%
%   Y = IDD2(X) computes the original signal from the approximation
%   coefficients matrix LL and details coefficients matrices 
%   LH, HL, HH, obtained by a wavelet decomposition of the 
%   original matrix and puts the result in Y.
%
%   The size of Y is the same as that of X which should be
%   a square matrix of size NxN where N is power of 2.
%   Minimum size of X is 4x4 where X should be arranged as 
%   [LL,LH;HL,HH].
%
%   See also DD2, DWTMODE, WAVEDEC2, WAVEINFO.

%   Auth: Dr. Bessam Z. Hassan
%   Last Revision: 27-Feb-2004.
%   Copyright 1995-2002 The MathWorks, Inc.
% $Revision: 1.0 $

%initialize coefficients

c0=(1+sqrt(3))/(4*sqrt(2));c1=(3+sqrt(3))/(4*sqrt(2));
c2=(3-sqrt(3))/(4*sqrt(2));c3=(1-sqrt(3))/(4*sqrt(2));

%check the inputs

[N,M]=size(Y);
if N~=2^round(log(N)/log(2))
    error('size of the input should be power of 2');
end
if M~=N
    error('the input matrix must be square');
end

% construct the W matrix

w=[c0,c1,c2,c3];wi=[c3,-c2,c1,-c0];
W=[];p=Y';
for i=1:N/2-1
    W(2*(i-1)+1:2*i,2*i-1:2*i+2)=[w;wi];
end
W=[W;[[w(3:4);wi(3:4)],zeros(2,N-4),[w(1:2);wi(1:2)]]];

% column shuffling

z(1:2:N,:)=p(1:N/2,:);z(2:2:N,:)=p(N/2+1:N,:);

% column inverse transformation

y=W'*z;

% row shuffling

p=y';
z(1:2:N,:)=p(1:N/2,:);z(2:2:N,:)=p(N/2+1:N,:);

% row inverse transformation

x=W'*z;