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.