Question: Locating edges in an image

Question: Locating edges in an image

Post by ICR - Mutual Grou » Fri, 14 Sep 1990 21:49:08


   I have built a scanning unit which basically takes cross sections of
a object passing under it on a conveyor and creates a 2D picture of
it in memory. (for example, a large peice of paper).  The image I build
is made only of a series of points outlining the object itself.  The
object passing under the scanner is roughly rectangular, (i.e. four edges)
but the edges can be somewhat bowed to make slightly concave or convex
sides.  There should be definate corners however.  For example, a (low
resolution) version of the image built might look like:
                     .
                   .    .
                 .         .             (With a lot more points, or course)
               .         .
                  .    .
                     .

  The problem is this.  Given the limited information that I receive
from the image, I must locate the edges of the object and calculate
each side's length (straight from one corner to the other, ignoring
the slight bow I mentioned earlier).  The result should be a *very*
accurate estimate of the height and width of the object and hence the
area it covers.

  Oh ya, one other twist, the object can come through in any orientation.
There is no guarantee a corner will always be first.

   Any ideas you have for algorithms, or documents you could point me
toward would be greatedly appreciated!  Like I said, an interesting
problem.