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<A HREF="toc.html">Contents</A>
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<A HREF="919Rotatingthegraphs.html">Previous</A>
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<A HREF="921Timingthegenerationofgraphs.html">Next</A>
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<HR NOSHADE>
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<H2><A NAME="9_20">9.20 Adjusting brightness and contrast for images and
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backgrounds</A></H2>
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<P><STRONG> The following section only applies to palette images. This
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means it wont work on true-color images.</STRONG></P>
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<P> It is often desirable to have a background image look a little bit
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"washed" out so it doesn't take the concentration away from the actual
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graph. There are basically two ways of accomplish this</P>
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<OL>
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<LI> Prepare the image with an external images editor to adjust the
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level of brightness and contrasty to a desirable level</LI>
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<LI> Use JpGraph:s built in adjustment for contrast, brightness and
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color saturation.</LI>
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</OL>
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<P> To adjust the background image call The levels for both brightness
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and contrast are real numbers in the range [-1, 1] You can choose to
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adjust for example just the background image or you might also choose
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to adjust the whole image. To change the background image just use the
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method <A href="../ref/Graph.html#_GRAPH_ADJBACKGROUNDIMAGE">
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Graph::AdjBackgroundImage()</A> to specify a suitable value. Let's show
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some example on what we can do with this. The following example have
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been generated by using the small utility "adjimg.php" which you can
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find in the "utils/" directory.</P>
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<P> <IMG alt="" border="0" HEIGHT="244" src="img/img/img/img/img/img/imgadj_orig.jpg" WIDTH="246">
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<BR> Brightness=0, contrast=0, saturation = -1 (Original image)</P>
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<P> <IMG alt="" border="0" HEIGHT="244" src="img/img/img/img/img/img/imgadj_b00c00sat-1.jpg" WIDTH="246">
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<BR> Brightness=0, contrast=0, saturation = -1 (Black & White image)</P>
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<P> <IMG alt="" border="0" HEIGHT="244" src="img/img/img/img/img/img/imgadj_b03c-03sat0.jpg" WIDTH="246">
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<BR> Brightness=0.3, contrast=-0.3, saturation=0</P>
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<P> <IMG alt="" border="0" HEIGHT="244" src="img/img/img/img/img/img/imgadj_b04c-07sat0.jpg" WIDTH="246">
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<BR> Brightness=0.4, contrast=-0.7, saturation=0</P>
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<P> <IMG alt="" border="0" HEIGHT="244" src="img/img/img/img/img/img/imgadj_b04c-07sat-1.jpg" WIDTH="246">
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<BR> Brightness=0.4, contrast=-0.7, saturation=-1</P>
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<P> <IMG alt="" border="0" HEIGHT="244" src="img/img/img/img/img/img/imgadj_b0c0sat1.jpg" WIDTH="246">
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<BR> Brightness=0, contrast=0, saturation=1</P>
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<A HREF="toc.html">Contents</A>
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<A HREF="919Rotatingthegraphs.html">Previous</A>
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<A HREF="921Timingthegenerationofgraphs.html">Next</A>
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