private void plotOverlay( Graphics2D g )
	{
		// If overlay drawing fails, just ignore it
		try 
		{
			File overlayImg = graphDef.getOverlay();
			if ( overlayImg != null )
			{
				BufferedImage img 	= ImageIO.read(overlayImg);
			
				int w 				= img.getWidth();
				int h 				= img.getHeight();
				int rgbWhite 		= Color.WHITE.getRGB(); 
				int pcolor, red, green, blue;

				// For better performance we might want to load all color
				// ints of the overlay in one go
				for (int i = 0; i < w; i++) {
					for (int j = 0; j < h; j++) {
						pcolor = img.getRGB(i, j);
						if ( pcolor != rgbWhite ) 
						{
							red 	= (pcolor >> 16) & 0xff;
							green 	= (pcolor >> 8) & 0xff;
							blue 	= pcolor & 0xff;

							g.setColor( new Color(red, green, blue) );
							g.drawLine( i, j, i, j );
						}
					}
				}
			}
		} catch (IOException e) {}	
	}