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       pgmedge - edge-detect a portable graymap


       pgmedge [pgmfile]


       Reads  a  portable graymap as input.  Outlines the edges, and writes a portable graymap as
       output.  Piping the result through pgmtopbm -threshold  and  playing  with  the  threshold
       value will give a bitmap of the edges.

       The  edge  detection  technique  used is to take the Pythagorean sum of two Sobel gradient
       operators at 90 degrees to each other.  For more details see "Digital Image Processing" by
       Gonzalez and Wintz, chapter 7.

       The  maxval of the output is the same as the maxval of the input The effect is better with
       larger maxvals, so you may want to increase the maxval of the input by running it  through
       pnmdepth first.


       pgmenhance(1), pgmtopbm(1), pnmdepth(1), pgm(5), pbm(5)


       Copyright (C) 1991 by Jef Poskanzer.

                                         04 February 1990                              pgmedge(1)