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  Engauge Digitizer - Discretizing</H2>
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<H2>What Is Discretizing?</H2>
<P>When an image is imported, Engauge Digitizer processes that image
  by converting each pixel into black or white. Since most images use
  black writing on a white background, the black pixels are
  assumed to represent curves, and the white pixels are assumed to
  represent the background. This process of converting color images into
  black foreground and white background is called <em>discretizing</em>.
  The resulting processed image can be automatically digitized
  using <A HREF="tutorautolinegraph.html#segmentfill">Segment Fill</A> and 
  <A HREF="tutorautopointgraph.html#pointmatch">Point Match</A>.</P>
<P>Usually the default discretizing settings correctly differentiate
  the foreground from the background. For example, in the two images
  below, the original image on the left gets processed into the image 
  on the right.</P>
<TABLE ALIGN="CENTER">
  <TR>
    <TD><IMG SRC="discretize_ok_before.png" ALT="OK before" WIDTH="247" HEIGHT="208"></TD>
    <TD><IMG SRC="discretize_ok_after.png" ALT="OK after" WIDTH="247" HEIGHT="208"></TD>
  </TR>
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    <TD ALIGN="CENTER">Before discretizing</TD>
    <TD ALIGN="CENTER">After discretizing</TD>
  </TR>
</TABLE>
<P>However, an image that uses color might not get correctly digitized. In
  the two images below, the original image on the left is processed into
  the featureless image on the right. The relatively dark green was 
  assumed to be part of the foreground.</P>
<TABLE ALIGN="CENTER">
  <TR>
    <TD><IMG SRC="discretize_bad_color_before.png" ALT="OK before" WIDTH="247" HEIGHT="208"></TD>
    <TD><IMG SRC="discretize_bad_color_after.png" ALT="OK after" WIDTH="247" HEIGHT="208"></TD>
  </TR>
  <TR>
    <TD ALIGN="CENTER">Before discretizing</TD>
    <TD ALIGN="CENTER">After discretizing</TD>
  </TR>
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<P>Even a black-and-white image might be discretized in a manner that
  is not very helpful. In the two images below, the original image on 
  the left is processed into the image on the right. 
  One curve is so thin it has broken up into many unconnected 
  short segments, and the other curve is so light that it has 
  disappeared entirely! Neither curve will be recognized
  by the curve recognition algorithms in Engauge Digitizer.</P>
<TABLE ALIGN="CENTER">
  <TR>
    <TD><IMG SRC="discretize_bad_gray_before.png" ALT="OK before" WIDTH="247" HEIGHT="208"></TD>
    <TD><IMG SRC="discretize_bad_gray_after.png" ALT="OK after" WIDTH="247" HEIGHT="208"></TD>
  </TR>
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    <TD ALIGN="CENTER">Before discretizing</TD>
    <TD ALIGN="CENTER">After discretizing</TD>
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<H2>How Do I Control Discretizing?</H2>
<P>By simply changing the Discretizing settings, curves can often be extracted 
  from color, low-contrast and low-resolution images. Such images are often 
  produced by fax machines, microfiche, cheap scanners, and excessive enlarging 
  on the copier.</P>
<P>Use the Settings/Discretizing dialog to experiment with various
  discretizing settings. You can get more information about the 
  <A HREF="dlgdiscretize.html">Discretizing dialog</A>.</P>
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