% Usage: Y = blkidct2(y, m, n).
% Block inverse DCT routine on array y, using m by n blocks.  m 
% must divide number of rows in y, n divide number of colums. 
% Transform returned in y. For small blocks it's faster to use 
% matrix multiplies than to repeatedly call the "dct2" command.

% If you don't have the signal processing toolbox substitute kdct() 
% for dct().

function y=blkidct2(Y,m,n)

  [r,s] = size(Y);
  y = zeros(r,s);
  C1 = idct(eye(m));
  C2 = idct(eye(n))';
  for i=1:(r/m)
      for j=1:(s/n)
          e = (i-1)*m+1;
          f = (j-1)*n+1;
          Z = double(Y(e:(e+m-1),(f:f+n-1)));
          y(e:(e+m-1),(f:f+n-1)) = C1*Z*C2;
      end;
  end;