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pgmedge(1)                             General Commands Manual                            pgmedge(1)



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 out‐
       put.  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 opera‐
       tors at 90 degrees to each other.  For more details see "Digital Image Processing" by  Gonza‐
       lez 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 pn‐‐
       mdepth 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)