Clean up scripts in image directory. Use Octave coding conventions. Redo docstrings. Add %!tests. * brighten.m: Put input validation first. Use iscolormap to simplify input checking. * cmunique.m: Use faster method of validating input class. * colormap.m: Tweak docstring. Improve input validation. * contrast.m: Tweak docstring. Use cmap instead of map as variable name for clarity. * gray2ind.m: Wrap long lines. Use faster method of validating input class. Delete unreachable code for n>65536. * hsv2rgb.m: Use faster method of validating input class. * imwrite.m: Tweak FIXME notes. * ind2gray.m: Use correct caller name for ind2x. Update %!tests with new 2-input calling convention. * ind2rgb.m: Tweak docstring. Update %!tests with new 2-input calling convention. * iscolormap.m: Tweak docstring. Re-order validation tests. * ntsc2rgb.m: Use faster method of validating input class. Better input validation. Add %!tests. * private/ind2x.m: Use more descriptive variable names. * rgb2hsv.m: Tweak docstring. Use faster method of validating input class. * rgb2ind.m: Tweak docstring. Wrap long lines. * rgb2ntsc.m: Use faster method of validating input class. Improve input validation. Add %!tests. * rgbplot.m: Match variable names in docstring to those in function prototype.

--- a/scripts/image/rgbplot.m
+++ b/scripts/image/rgbplot.m
@@ -50,7 +50,7 @@
   endif
 
   if (! iscolormap (cmap))
-    error ("rgbplot: CMAP must be a colormap");
+    error ("rgbplot: CMAP must be a valid colormap");
   elseif (! ischar (style))
     error ("rgbplot: STYLE must be a string");
   endif
@@ -69,7 +69,7 @@
   xlabel ("color index");
 
   if (nargout > 0)
-    retval = h;
+    h = htmp;
   endif
 
 endfunction
@@ -81,7 +81,8 @@
 %! subplot (1, 2, 2)
 %! rgbplot (ocean, "composite");
 
-%%test input validation
+%% Test input validation
 %!error rgbplot ()
 %!error rgbplot (1,2)
-%!error <CMAP must be a colormap> rgbplot ({0 1 0})
+%!error <CMAP must be a valid colormap> rgbplot ({0 1 0})
+