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)
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