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  28  <H3><A NAME="10_18_1">10.18.1 Enabling anti-aliased lines</A></H3>
  29  <P> Anti-aliased lines are enabled by calling the method <A href="../ref/Image.html#_IMAGE_SETANTIALIASING">
  30   SetAntiAliasing()</A> in the <A href="../ref/Image.html#_C_IMAGE">
  31   Image class</A> in the script where you want to use anti-aliasing.</P>
  32  <P> The anti-aliasing for lines works by &quot;smoothing&quot; out the edges on
  33   the line by using a progressive scale of colors interpolated between
  34   the background color and the line color.</P>
  35  <P><DIV class="note"><B>Note:</B> The algorithm used for anti-aliasing
  36   of lines is quite simple. It would be possible to achieve even better
  37   result by doing some real 2D signal processing. However, doing real
  38   time 2D signal processing on a HTTP server would be foolish so the
  39   design is deliberately kept simple. To achieve best visual result
  40   always use a dark line color on a light background.</DIV></P>
  41  <P> An example will show that this, quite simple algorithm, gives a
  42   reasonable good result. The figures below shows a radar plot with and
  43   without anti-aliasing.</P>
  44  <P><DIV class="example">
  45  <BR> <A href="exframes/frame_radarex8.html" target="blank"><IMG border="0"
  46  HEIGHT="200"  src="img/radarex8.png" WIDTH="300"></A>
  47  <BR><B>Figure 170:</B> Spiderplot without anti-aliasing <A href="exframes/frame_radarex8.html"
  48  target="blank">[src]</A>&nbsp;
  49  <P></P>
  50  </DIV></P>
  51  <P></P>
  52  <P><DIV class="example">
  53  <BR> <A href="exframes/frame_radarex8.1.html" target="blank"><IMG border="0"
  54  HEIGHT="200"  src="img/radarex8.1.png" WIDTH="300"></A>
  55  <BR><B>Figure 171:</B> Spiderplot with anti-aliasing <A href="exframes/frame_radarex8.1.html"
  56  target="blank">[src]</A>&nbsp;
  57  <P></P>
  58  </DIV></P>
  59  <P></P>
  60  <P> One thing you need to keep in mind when deciding to use
  61   anti-aliasing is that it could have potentially a dramatic effect on
  62   the time it takes to generate the image. Line drawing with
  63   anti-aliasing turned on is roughly 8 times slower than the normal line
  64   drawing so treat this feature wisely.</P>
  65  <P> Furthermore there are a couple of &quot;gotchas&quot; you should be aware of
  66   when using anti-aliasing.</P>
  67  <OL>
  68  <LI> Anti-aliased lines uses up more of the available color-palette. The
  69   exact number of colors used is dependent on the line-angle, a near
  70   horizontal or near vertical line uses more colors (number of lines with
  71   different angles uses more colors). Hence it might not be possible to
  72   use anti-aliasing with color-gradient fill since the number of
  73   available colors in the palette might not be enough. A normal palette
  74   can keep around 256 colors. This means that you are advised to use a
  75   true-color image when using anti-aliasing.</LI>
  76  <LI> Anti-aliasing does not work very well together with background
  77   images since it assumes a the same solid color on each side of the
  78   line. Doing a more advanced anti-aliasing algorithm would simple take
  79   to much processing power.</LI>
  80  <LI>Anti-aliased lines will ignore the line width specified. They will
  81   always have a width of roughly 1.</LI>
  82  </OL>
  83  <P></P>
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