dct2.m

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function b=dct2(arg1,mrows,ncols)
%DCT2 Compute 2-D discrete cosine transform.
%   B = DCT2(A) returns the discrete cosine transform of A.
%   The matrix B is the same size as A and contains the
%   discrete cosine transform coefficients.
%
%   B = DCT2(A,[M N]) or B = DCT2(A,M,N) pads the matrix A with
%   zeros to size M-by-N before transforming. If M or N is
%   smaller than the corresponding dimension of A, DCT2 truncates
%   A. 
%
%   This transform can be inverted using IDCT2.
%
%   Class Support
%   -------------
%   A can be of class uint8 or double. The returned matrix B is
%   of class double.
%
%   Example
%   -------
%       RGB = imread('autumn.tif');
%       I = rgb2gray(RGB);
%       J = dct2(I);
%       imshow(log(abs(J)),[]), colormap(jet), colorbar
%
%   The commands below set values less than magnitude 10 in the
%   DCT matrix to zero, then reconstruct the image using the
%   inverse DCT function IDCT2.
%
%       J(abs(J)<10) = 0;
%       K = idct2(J);
%       imshow(I), figure, imshow(K,[0 255])
%
%   See also FFT2,IFFT2,IDCT2.

%   Clay M. Thompson 10-6-92
%   Copyright 1993-1998 The MathWorks, Inc.  All Rights Reserved.
%   $Revision: 5.9 $  $Date: 1997/11/24 15:34:27 $

%   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),
    b = dct(dct(arg1).').';
    return;
  else
    mrows = m;
    ncols = n;
  end
end

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

% Transform.

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