--- a/main/image/inst/isgray.m	Fri Nov 24 11:55:54 2006 +0000
+++ b/main/image/inst/isgray.m	Fri Nov 24 16:33:11 2006 +0000
@@ -16,8 +16,12 @@
 
 ## -*- texinfo -*-
 ## @deftypefn {Function File} @var{bool}= isgray (@var{I})
-## returns true for an intensity image. All intensity values must
-## be in the range [0,1].
+## returns true for an 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>
@@ -25,16 +29,18 @@
 
 function bool = isgray (I)
 
-  bool = 0;
-
-  if !(nargin == 1)
-    usage ("isgray(I)");
+  if (nargin != 1)
+    print_usage ();
   endif
 
-  if (!is_matrix(I))
-    return;
+  bool = false;
+  if (ismatrix(I) && ndims(I) == 2)
+    switch(class(I))
+    case "double"
+      bool = all(I(:) >= 0 && I(:) <= 1);
+    case {"uint8", "uint16"}
+      bool = true;
+    endswitch
   endif
 
-  bool = all (all ((I >= 0) && (I <= 1)));
-
 endfunction

--- a/main/image/inst/rgb2gray.m	Fri Nov 24 11:55:54 2006 +0000
+++ b/main/image/inst/rgb2gray.m	Fri Nov 24 16:33:11 2006 +0000
@@ -15,33 +15,42 @@
 ## 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.
+## @deftypefn {Function File} @var{gray}= rgb2gray (@var{rgb})
+## Converts an RGB image to a gray scale image, or a color map
+## to a gray map.
+##
+## If the input is an RGB image, the conversion to a gray image
+## is computed as the mean value of the color channels.
+##
+## If the input is a color map it 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)
+function gray = rgb2gray (rgb)
 
   if (nargin != 1)
-    usage ("graymap = rgb2gray (map)");
+    print_usage();
   endif
 
-  msg = "rgb2gray: argument must be a matrix of size n x 3";
-  if (! is_matrix (rgb))
-    error (msg);
+  if (ismatrix (rgb) && ndims(rgb) == 2 && columns(rgb) == 3)
+    ntscmap = rgb2ntsc (rgb);
+    gray = ntscmap (:, 1) * ones (1, 3);
+  elseif (ismatrix(rgb) && ndims(rgb) == 3)
+    switch(class(rgb))
+    case "double"
+      gray = mean(rgb,3);
+    case "uint8"
+      gray = uint8(mean(rgb,3));
+    case "uint16"
+      gray = uint16(mean(rgb,3));
+    otherwise
+      error("rgb2gray: unsupported class %s", class(rgb));
+    endswitch
+  else
+    error("rgb2gray: the input must either be an RGB image or a color map");
   endif
-
-  nc = columns (rgb);
-  if (nc != 3)
-    error (msg);
-  endif
-
-  ntscmap = rgb2ntsc (rgb);
-
-  graymap = ntscmap (:, 1) * ones (1, 3);
 endfunction