antialias lines

[Bailey Landress]

Trying to fix jagged lines.  See anything wrong with the Mapfile below? 
When I change IMAGEMODE to RGBA the background of my map turns black.  Also
if I take out   SYMBOL "cartoline" from the Style tag under Layer, I do not
see any change in regard to antialiasing.  Any help would be greatly
appreciated.  Thanks.

MapServer version 4.10.2

In MAP:

IMAGETYPE png24

OUTPUTFORMAT
   	  NAME png24
	  DRIVER "GD/PNG"
	  MIMETYPE "image/png"
	  IMAGEMODE RGB
	  EXTENSION "png"
END   

SYMBOL
	  NAME 'cartoline'
	  TYPE cartoline
	  LINECAP round
 	  LINEJOIN round
	  LINEJOINMAXSIZE 3
END



LAYER
	 NAME "Contours"
	 STATUS on
	 TYPE LINE
	 DATA "Contours"
	 SYMBOLSCALE 24000
	 TRANSPARENCY alpha
	 CLASS
	 	  STYLE
		  	   COLOR 000 000 000
			   SYMBOL "cartoline"
			   ANTIALIAS TRUE
			   WIDTH 2
	    	   END
	 END
END	


Bailey