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+## Copyright (C) 2000, 2001  Kai Habel
+##
+## This program 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 2 of the License, or
+## (at your option) any later version.
+##
+## This program 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 this program; if not, write to the Free Software
+## Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+
+## -*- texinfo -*-
+## @deftypefn {Function File} @var{I}= rgb2gray (@var{M})
+## converts a color map to a gray map. 
+## The RGB map is converted into the YIQ space of ntsc. The luminance
+## value (Y) is taken to create a gray color map.
+## R = G = B = Y
+## @end deftypefn
+
+## Author:	Kai Habel <kai.habel@gmx.de>
+## Date:	19. March 2000
+
+function graymap = rgb2gray (rgb)
+
+  if (nargin != 1)
+    usage ("graymap = rgb2gray (map)");
+  endif
+
+  msg = "rgb2gray: argument must be a matrix of size n x 3";
+  if (! is_matrix (rgb))
+    error (msg);
+  endif
+
+  nc = columns (rgb);
+  if (nc != 3)
+    error (msg);
+  endif
+
+  ntscmap = rgb2ntsc (rgb);
+
+  graymap = ntscmap (:, 1) * ones (1, 3);
+endfunction