DCT.rar_TRANSFORMATION

function x=irdct(y,n,a,b) %IRDCT Inverse discrete cosine transform of real data X=(Y,N) % Data is truncated/padded to length N. % % This routine is equivalent to multiplying by the matrix % % irdct(eye(n)) = cos((0.5:n)'*(0:n-1)*pi/n)*diag([sqrt(0.5)*a/b repmat(a,1,n-1)])/n % % % Default values of the scaling factors are A=sqrt(2N) and B=1 which % results in an orthogonal matrix. Other common values are A=1 or N and/or B=1 or sqrt(2). % If b~=1 then the columns are no longer orthogonal. % See also RCDT % Copyright (C) Mike Brookes 1998 % Version: $Id: irdct.m,v 1.4 2007/05/04 07:01:38 dmb Exp $ % % VOICEBOX is a MATLAB toolbox for speech processing. % Home page: http://www.ee.ic.ac.uk/hp/staff/dmb/voicebox/voicebox.html % %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% % This program is free software; you can redistribute it and/or modify % it under the terms of the GNU General Public License as published by % the Free Software Foundation; either version 2 of the License, or % (at your option) any later version. % % This program is distributed in the hope that it will be useful, % but WITHOUT ANY WARRANTY; without even the implied warranty of % MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the % GNU General Public License for more details. % % You can obtain a copy of the GNU General Public License from % http://www.gnu.org/copyleft/gpl.html or by writing to % Free Software Foundation, Inc.,675 Mass Ave, Cambridge, MA 02139, USA. %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% fl=size(y,1)==1; if fl y=y(:); end [m,k]=size(y); if nargin<4 b=1; if nargin<3 a=sqrt(2*m); if nargin<2 n=m; end end end if n>m y=[y; zeros(n-m,k)]; elseif n<m y(n+1:m,:)=[]; end x=zeros(n,k); w=ones(1,k); m=fix((n+1)/2); p=n-m; z=0.5*exp((0.5i*pi/n)*(1:p)).'; u=(y(2:p+1,:)-1i*y(n:-1:m+1,:)).*z(:,w)*a; y=[y(1,:)*sqrt(0.5)*a/b; u(1:m-1,:)]; if m==p z=-0.5i*exp((2i*pi/n)*(0:m-1)).'; y=(z(:,w)+0.5).*(conj(flipud(u))-y)+y; z=ifft(y,[],1); u=real(z); y=imag(z); q=m/2; h=rem(m,2)/2; x(1:4:n,:)=u(1:q+h,:); x(2:4:n,:)=y(m:-1:q+1-h,:); x(3:4:n,:)=y(1:q-h,:); x(4:4:n,:)=u(m:-1:q+1+h,:); else z=real(ifft([y; conj(flipud(u))])); x(1:2:n,:)=z(1:m,:); x(2:2:n,:)=z(n:-1:m+1,:); end if fl x=x.'; end