pbmclean - despeckle a PBM image
pbmclean [-minneighbors=N] [-black|-white] [-extended] [pbmfile]
You can use the minimum unique abbreviation of the options. You can use two hyphens instead of one. You can separate an option name from its value with white space instead of an equals sign.
This program is part of Netpbm(1).
pbmclean cleans up a PBM image of random specks. It reads a PBM image as input and outputs a PBM that is the same as the input except with isolated pixels inverted.
You can use pbmclean to clean up "snow" on bitmap images.
There are two ways pbmclean can define "isolated" pixels: simple and extended. When you specify -extended, pbmclean uses extended; otherwise it uses basic.
In basic mode, pbmclean looks at each pixel individually, and any pixel that doesn't have at least a minimum number of pixels of the same color touching it is considered isolated and pbmclean erases it.
The -minneighbors option specifies the minimum number of neighboring pixels of the same color for a pixel not to be considered isolated.
For example, if -minneighbors is two and there are two contiguous black pixels in an otherwise white field, each of those pixels is isolated, so pbmclean erases them - turns both white.
The default minimum 1 pixel - pbmclean flips only completely isolated pixels.
(A -minneighbors value greater than 8 generates a completely inverted image (but use pnminvert to do that) -- or a completely white or completely black image with the -black or -white option).
pbmclean considers the area beyond the edges of the image to be white. (This matters when you consider pixels right on the edge of the image).
pbmclean does not distinguish between foreground and background; by default, it flips isolated pixels of either color. But you can specify -black or -white to have it flip only pixels of one color.
In extended mode, pbmclean erases all blobs which don't have the specified minimum number of pixels. A blob is a set of contiguous pixels of the foreground color. The minimum number of pixels is one plus the -minneighbors value. You specify the foreground color with -black and -white (default is black).
For example, if -minneighbors is 2 and the foreground color is black, and the image contains a straight line 4 pixels long, pbmclean erases that -- turns all four pixels white. pbmclean also erases 4 pixels in a square or L-shape.
The default -minneighbors is 4, so a blob must have at least 5 pixels to escape pbmclean's purge.
Extended mode was new in Netpbm 10.56 (September 2011).
Before December 2001, pbmclean accepted -N instead of -minneighbors. Before Netpbm 10.27 (March 2005), -minneighbors was -minneighbor.
This option was new in Netpbm 10.56 (September 2011).
Copyright (C) 1990 by Angus Duggan Copyright (C) 1989 by Jef Poskanzer. Copyright (C) 2001 by Michael Sternberg.
Permission to use, copy, modify, and distribute this software and its documentation for any purpose and without fee is hereby granted, provided that the above copyright notice appear in all copies and that both that copyright notice and this permission notice appear in supporting documentation. This software is provided "as is" without express or implied warranty.