% Copyright (C) 1994-2013 John W. Eaton
%
% This file is part of Octave.
%
% Octave is free software; you can redistribute it and/or modify it
% under the terms of the GNU General Public License as published by
% the Free Software Foundation; either version 3 of the License, or (at
% your option) any later version.
%
% Octave is distributed in the hope that it will be useful, but
% WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
% General Public License for more details.
%
% You should have received a copy of the GNU General Public License
% along with Octave; see the file COPYING.  If not, see
% <http://www.gnu.org/licenses/>.

% -*- texinfo -*-
% @deftypefn {Function File} {@var{I} =} ind2gray (@var{x}, @var{map})
% Convert a color indexed image to a grayscale intensity image.
%
% The image @var{x} must be an indexed image which will be converted using the
% colormap @var{cmap}.  If @var{cmap} does not contain enough colors for the
% image, pixels in @var{x} outside the range are mapped to the last color in
% the map before conversion to grayscale.
%
% The output @var{I} is of the same class as the input @var{x} and may be
% one of @code{uint8}, @code{uint16}, @code{single}, or @code{double}.
%
% Implementation Note: There are several ways of converting colors to
% grayscale intensities.  This functions uses the luminance value obtained
% from @code{rgb2ntsc} which is @code{I = 0.299*R + 0.587*G + 0.114*B}.
% Other possibilities include the value component from @code{rgb2hsv} or
% using a single color channel from @code{ind2rgb}.
% @seealso{gray2ind, ind2rgb}
% @end deftypefn

% Author: Tony Richardson <arichard@stark.cc.oh.us>
% Created: July 1994
% Adapted-By: jwe

function I = ind2gray (x, map)

  if (nargin ~= 2)
    print_usage ();
  end
  [x, map] = ind2x ('ind2gray', x, map);

  % Convert colormap to luminance intensity values 
  map = map * [0.29894; 0.58704; 0.11402];

  % Convert colormap to same class as that of input so that reshape
  % will produce output of the same type as the input.
  cls = class (x);
  if (isinteger (x))
    % if we later add support for int16 images, this will not work. Look into
    % im2int16 from image package for such case
    map = map * intmax (cls);
  elseif (strcmp (cls, 'single'))
    map = single (map);
  end

  % Replace indices in the input matrix with the indexed luminance value.
  I = reshape (map(x(:)), size (x));