function X=extract(M)

%    Extraction of non-overlapping 8x8 blocks
%
%    ===========================================================
%    
%    function description:
%    
%    This function chops up the matrix into subblocks of 
%    size 8x8. Subsequently it converts each block into a column
%    vector. The output is a 64x1024 matrix consisting of these
%    column vectors.

for rowblock = 1:size(M,1)/8
  for colblock =1:size(M,2)/8
    for rowOfPxls = 1:8
      for colOfPxls = 1:8
	% create block of size 8x8 out of the matrix
	block(rowOfPxls, colOfPxls) = M((rowblock - 1)*8 + ...
	    rowOfPxls, (colblock - 1)*8 + colOfPxls);
      end
    end
    X(:, rowblock + (colblock - 1)*32) = block(:);
  end
end