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 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)
Check Out this Related Man Page
pnmdepth(1) General Commands Manual pnmdepth(1)NAME
pnmdepth - change the maxval in a portable anymap
SYNOPSIS
pnmdepth newmaxval [pnmfile]
DESCRIPTION
Reads a portable anymap as input. Scales all the pixel values, and writes out the image with the new maxval. Scaling the colors down to a
smaller maxval will result in some loss of information.
Be careful of off-by-one errors when choosing the new maxval. For instance, if you want the color values to be five bits wide, use a max-
val of 31, not 32.
One important use of pnmdepth is to convert a new format 2-byte-per-sample PNM file to the older 1-byte-per-sample format. Before April
2000, essentially all raw (binary) format PNM files had a maxval less than 256 and one byte per sample, and many programs may rely on that.
If you specify a newmaxval less than 256, the resulting file should be readable by any program that worked with PNM files before April
2000.
SEE ALSO pnm(5), ppmquant(1), ppmdither(1)AUTHOR
Copyright (C) 1989, 1991 by Jef Poskanzer.
08 April 2000 pnmdepth(1)
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