Linux Commands Examples

A great documentation place for Linux commands


edge-detect a portable graymap

see also : pgmenhance - pgmtopbm - pnmdepth


pgmedge [pgmfile]

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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 , pgmtopbm , pnmdepth , pgm, pbm


Copyright (C) 1991 by Jef Poskanzer.

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