--- /dev/null
+## Copyright (C) 2000 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, see <http://www.gnu.org/licenses/>.
+
+## -*- texinfo -*-
+## @deftypefn {Function File} @var{bool}= isgray (@var{I})
+## Returns true for an gray-scale intensity image. An variable is a gray scale image
+## if it is 2-dimensional matrix, and
+## @itemize @bullet
+## @item is of class double and all values are in the range [0, 1], or
+## @item is of class uint8 or uint16.
+## @end itemize
+## @end deftypefn
+
+## Author: Kai Habel <kai.habel@gmx.de>
+## Date: 20/03/2000
+
+function bool = isgray (I)
+
+ if (nargin != 1)
+ print_usage ();
+ endif
+
+ bool = false;
+ if (ismatrix(I) && ndims(I) == 2)
+ switch(class(I))
+ case "double"
+ bool = all((I(:) >= 0 & I(:) <= 1) | isnan(I(:)));
+ case {"uint8", "uint16"}
+ bool = true;
+ endswitch
+ endif
+
+endfunction