function [prim, hidd] = decodeImage(fname)
  % DECODEIMAGE  Decode embedded image.
  %   DECODEIMAGE(IMAGEFILE) decodes embedded image file IMAGEFILE.
  %   IMAGEFILE must be a valid file name. It will display a figure with 3
  %   axes. The top axis is the original image. The bottom left is the
  %   primary image, and the bottom right is the embedded hidden image.
  %
  %   [PRIMARY, HIDDEN] = DECODEIMAGE(IMAGEFILE) returns the primary image
  %   and the hidden image data as RGB data.
  %
  %   This function only works on images created by embedImage.m.
  %
  %   Example:
  %     % create embedded image
  %     embedImage('trees.tif', 'football.jpg');
  %     decodeImage('trees_football.png');
  %
  %   See also EMBEDIMAGE.
  %
  % Jiro Doke
  % Jan 24, 2009.

  % Error check
  error(nargchk(1, 1, nargin, 'struct'));
  error(nargchk(0, 2, nargout, 'struct'));
  validateattributes(fname, {'char'}, {'row'});
  
  if ~exist(fname, 'file')
    error('Utility:decodeImage:FileNotFound', ...
      'File not found.');
  end
  
  fInfo = imfinfo(fname);
  if ~isfield(fInfo, 'Comment') || ...
      ~ischar(fInfo.Comment) || ...
      ~strcmp(fInfo.Comment, 'Created by embedImage.m')
    error('Utility:decodeImage:InvalidFile', ...
      'This only works with image files created by embedImage.m');
  end
  
  imData = imread(fname);
  pixelVals = imData(:);
  pixelVals_conv = typecast(pixelVals, 'uint8');
  pixelVals_conv = reshape(pixelVals_conv, 2, [])';
  imData_primary = reshape(pixelVals_conv(:, 2), size(imData));
  imData_hidden  = reshape(pixelVals_conv(:, 1), size(imData));
  
  if nargout == 0
    figure;
    subplot(2,1,1);imshow(imData, 'Border', 'tight');title('Original Image');
    subplot(2,2,3);imshow(imData_primary, 'Border', 'tight');title('Primary Image');
    subplot(2,2,4);imshow(imData_hidden, 'Border', 'tight');title('Embedded Image');
  else
    prim = imData_primary;
    if nargout > 1
      hidd = imData_hidden;
    end
  end
  
end