NAME

       pgmedge - edge-detect a portable graymap

SYNOPSIS

       pgmedge [pgmfile]

DESCRIPTION

       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.

SEE ALSO

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

AUTHOR

       Copyright (C) 1991 by Jef Poskanzer.

                                                04 February 1990                                      pgmedge(1)