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  28  <H2><A NAME="10_20">10.20 Adjusting brightness and contrast for images
  29   and backgrounds</A></H2>
  30  <P><STRONG> The following section only applies to palette images. This
  31   means it wont work on true-color images.</STRONG></P>
  32  <P> It is often desirable to have a background image look a little bit
  33   &quot;washed&quot; out so it doesn't take the concentration away from the actual
  34   graph. There are basically two ways of accomplish this</P>
  35  <OL>
  36  <LI> Prepare the image with an external images editor to adjust the
  37   level of brightness and contrasty to a desirable level</LI>
  38  <LI> Use JpGraph:s built in adjustment for contrast, brightness and
  39   color saturation.</LI>
  40  </OL>
  41  <P> To adjust the background image call The levels for both brightness
  42   and contrast are real numbers in the range [-1, 1] You can choose to
  43   adjust for example just the background image or you might also choose
  44   to adjust the whole image. To change the background image just use the
  45   method <A href="../ref/Graph.html#_GRAPH_ADJBACKGROUNDIMAGE">
  46   Graph::AdjBackgroundImage()</A> to specify a suitable value. Let's show
  47   some example on what we can do with this. The following example have
  48   been generated by using the small utility &quot;adjimg.php&quot; which you can
  49   find in the &quot;utils/&quot; directory.</P>
  50  <P> <IMG alt="" border="0" HEIGHT="244"  src="img/imgadj_orig.jpg" WIDTH="246">
  51  <BR> Brightness=0, contrast=0, saturation = -1 (Original image)</P>
  52  <P> <IMG alt="" border="0" HEIGHT="244"  src="img/imgadj_b00c00sat-1.jpg" WIDTH="246">
  53  <BR> Brightness=0, contrast=0, saturation = -1 (Black &amp; White image)</P>
  54  <P> <IMG alt="" border="0" HEIGHT="244"  src="img/imgadj_b03c-03sat0.jpg" WIDTH="246">
  55  <BR> Brightness=0.3, contrast=-0.3, saturation=0</P>
  56  <P> <IMG alt="" border="0" HEIGHT="244"  src="img/imgadj_b04c-07sat0.jpg" WIDTH="246">
  57  <BR> Brightness=0.4, contrast=-0.7, saturation=0</P>
  58  <P> <IMG alt="" border="0" HEIGHT="244"  src="img/imgadj_b04c-07sat-1.jpg" WIDTH="246">
  59  <BR> Brightness=0.4, contrast=-0.7, saturation=-1</P>
  60  <P> <IMG alt="" border="0" HEIGHT="244"  src="img/imgadj_b0c0sat1.jpg" WIDTH="246">
  61  <BR> Brightness=0, contrast=0, saturation=1</P>
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