--- a/scripts/image/ind2gray.m	Sun Mar 16 11:44:11 2014 -0700
+++ b/scripts/image/ind2gray.m	Mon Mar 17 09:10:32 2014 -0700
@@ -69,18 +69,19 @@
 
 %!shared i2g
 %! i2g = ind2gray (1:100, gray (100));
-%!assert (i2g, 0:1/99:1, eps);
-%!assert (gray2ind (i2g, 100), uint8 (0:99));
+%!
+%!assert (i2g, 0:1/99:1, eps)
+%!assert (gray2ind (i2g, 100), uint8 (0:99))
 
 %% Test input validation
 %!error ind2gray ()
 %!error ind2gray (1)
 %!error ind2gray (1,2,3)
-%!error <X must be an indexed image> ind2gray ({1}, jet (64))
+%!error <X must be an indexed image> ind2gray (ones (3,3,3), jet (64))
 %!error <X must be an indexed image> ind2gray (1+i, jet (64))
 %!error <X must be an indexed image> ind2gray (sparse (1), jet (64))
-%!error <X must be an indexed image> ind2gray (0, jet (64))
 %!error <X must be an indexed image> ind2gray (1.1, jet (64))
+%!error <X must be an indexed image> ind2gray ({1}, jet (64))
 %!error <MAP must be a valid colormap> ind2gray (1, {1})
 %!error <MAP must be a valid colormap> ind2gray (1, 1+i)
 %!error <MAP must be a valid colormap> ind2gray (1, ones (2,2,2))
@@ -88,3 +89,7 @@
 %!error <MAP must be a valid colormap> ind2gray (1, [-1])
 %!error <MAP must be a valid colormap> ind2gray (1, [2])
 
+%!warning <contains colors outside of colormap> ind2gray ([0 1 2], gray (5));
+%!warning <contains colors outside of colormap> ind2gray ([1 2 6], gray (5));
+%!warning <contains colors outside of colormap> ind2gray (uint8 ([1 2 5]), gray (5));
+

--- a/scripts/image/ind2rgb.m	Sun Mar 16 11:44:11 2014 -0700
+++ b/scripts/image/ind2rgb.m	Mon Mar 17 09:10:32 2014 -0700
@@ -82,23 +82,28 @@
 %! ## test basic usage with 1 and 3 outputs
 %! [rgb] = ind2rgb (img, map);
 %! [r, g, b] = ind2rgb (img, map);
-%!assert (ergb, rgb);
-%!assert (ergb, reshape ([r(:) g(:) b(:)], [size(img) 3]));
+%!
+%!assert (ergb, rgb)
+%!assert (ergb, reshape ([r(:) g(:) b(:)], [size(img) 3]))
+%!test
 %! ## test correction for integers
-%! img = uint8 (img -1);
+%! img = uint8 (img - 1);
 %! [rgb] = ind2rgb (img, map);
-%!assert (ergb, rgb);
-%! ## check it fails when image is a float with an index value of 0
-%!fail ("[rgb] = ind2rgb (double(img), map)")
+%! assert (ergb, rgb);
+%!test
+%! ## Check that values below lower bound are mapped to first color value 
+%! rgb = ind2rgb ([-1 0 2], gray (64));
+%! assert (rgb(:,1:2,:), zeros (1,2,3));
+%! assert (rgb(:,3,:), 1/63 * ones (1,1,3));
 
 %% Test input validation
 %!error ind2rgb ()
 %!error ind2rgb (1,2,3)
-%!error <X must be an indexed image> ind2rgb ({1}, jet (64))
+%!error <X must be an indexed image> ind2rgb (ones (3,3,3), jet (64))
 %!error <X must be an indexed image> ind2rgb (1+i, jet (64))
 %!error <X must be an indexed image> ind2rgb (sparse (1), jet (64))
-%!error <X must be an indexed image> ind2rgb (0, jet (64))
 %!error <X must be an indexed image> ind2rgb (1.1, jet (64))
+%!error <X must be an indexed image> ind2rgb ({1}, jet (64))
 %!error <MAP must be a valid colormap> ind2rgb (1, {1})
 %!error <MAP must be a valid colormap> ind2rgb (1, 1+i)
 %!error <MAP must be a valid colormap> ind2rgb (1, ones (2,2,2))
@@ -106,3 +111,8 @@
 %!error <MAP must be a valid colormap> ind2rgb (1, [-1])
 %!error <MAP must be a valid colormap> ind2rgb (1, [2])
 
+%!warning <contains colors outside of colormap> ind2rgb ([-1 1], jet (64));
+%!warning <contains colors outside of colormap> ind2rgb ([0 1 2], gray (5));
+%!warning <contains colors outside of colormap> ind2rgb ([1 2 6], gray (5));
+%!warning <contains colors outside of colormap> ind2rgb (uint8 ([1 2 5]), gray (5));
+

--- a/scripts/image/private/ind2x.m	Sun Mar 16 11:44:11 2014 -0700
+++ b/scripts/image/private/ind2x.m	Mon Mar 17 09:10:32 2014 -0700
@@ -22,12 +22,13 @@
 function [x, map] = ind2x (caller, x, map)
 
   ## Check if X is an indexed image.
-  ## an indexed image is defined has having only 2D, and that's how Matlab
+  ## An indexed image is defined has having only 2D, and that's how Matlab
   ## behaves.  But we want to support ND images, so we will allow up to 4D
-  ## and check that the 3rd is a singleton
-  if (all (ndims (x) != [2 4]) || size (x, 3) != 1 || issparse (x) ||
-      (isfloat (x) && ! isindex (x)) ||
-      ! any (strcmp (class (x), {"uint8", "uint16", "single", "double"})))
+  ## and check that the 3rd dimension is a singleton.
+  if (all (ndims (x) != [2 4]) || size (x, 3) != 1
+      || iscomplex (x) || issparse (x)
+      || (isfloat (x) && x != fix (x))
+      || ! any (strcmp (class (x), {"uint8", "uint16", "single", "double"})))
     error ("%s: X must be an indexed image", caller);
   endif
 
@@ -36,10 +37,20 @@
     error ("%s: MAP must be a valid colormap", caller);
   endif
 
-  ## Do we have enough colors in the color map?
-  ## there's an offset of 1 when the indexed image is an integer class so we fix
-  ## it now and convert it to float only if really necessary and even then only
-  ## to single precision since that is enough for both uint8 and uint16.
+  ## Any color indices below the lower bound of the color map are modified
+  ## to point to the first color in the map (see bug #41851).
+  if (isfloat (x))
+    invalid_idx = x < 1;
+    if (any (invalid_idx(:)))
+      warning (["Octave:" caller ":invalid-idx-img"],
+               [caller ": indexed image contains colors outside of colormap"]);
+      x(invalid_idx) = 1;
+    endif
+  endif
+
+  ## Switch to using 1-based indexing.
+  ## It is possible that an integer storage class may not have enough room
+  ## to make the switch, in which case we convert the data to single.
   maxidx = max (x(:));
   if (isinteger (x))
     if (maxidx == intmax (class (x)))
@@ -49,9 +60,12 @@
     maxidx += 1;
   endif
 
+  ## When there are more colors in the image, than there are in the map,
+  ## pad the colormap with the last color in the map for Matlab compatibility.
   num_colors = rows (map);
   if (num_colors < maxidx)
-    ## Pad with the last color in the map for Matlab compatibility
+    warning (["Octave:" caller ":invalid-idx-img"],
+             [caller ": indexed image contains colors outside of colormap"]);
     pad = repmat (map(end,:), maxidx - num_colors, 1);
     map(end+1:maxidx, :) = pad;
   endif