idct2.m

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function a = idct2(arg1,mrows,ncols)
%IDCT2 Compute 2-D inverse discrete cosine transform.
%   B = IDCT2(A) returns the two-dimensional inverse discrete
%   cosine transform of A.
%
%   B = IDCT2(A,[M N]) or B = IDCT2(A,M,N) pads A with zeros (or
%   truncates A) to create a matrix of size M-by-N before
%   transforming. 
%
%   For any A, IDCT2(DCT2(A)) equals A to within roundoff error.
%
%   The discrete cosine transform is often used for image
%   compression applications.
%
%   Class Support
%   -------------
%   The input matrix A can be of class uint8 or double. The
%   output matrix B is of class double.
%
%   See also DCT2, DCTMTX, FFT2, IFFT2.

%   Clay M. Thompson 10-6-92
%   Copyright 1993-1998 The MathWorks, Inc.  All Rights Reserved.
%   $Revision: 5.6 $  $Date: 1997/11/24 15:35:10 $

%   References: 
%   1) A. K. Jain, "Fundamentals of Digital Image
%      Processing", pp. 150-153.
%   2) Wallace, "The JPEG Still Picture Compression Standard",
%      Communications of the ACM, April 1991.

[m, n] = size(arg1);
% Basic algorithm.
if (nargin == 1),
  if (m > 1) & (n > 1),
    a = idct(idct(arg1).').';
    return;
  else
    mrows = m;
    ncols = n;
  end
end

% Padding for vector input.

b = arg1;
if nargin==2, ncols = mrows(2); mrows = mrows(1); end
mpad = mrows; npad = ncols;
if m == 1 & mpad > m, b(2, 1) = 0; m = 2; end
if n == 1 & npad > n, b(1, 2) = 0; n = 2; end
if m == 1, mpad = npad; npad = 1; end   % For row vector.

% Transform.

a = idct(b, mpad);
if m > 1 & n > 1, a = idct(a.', npad).'; end