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.
Before December 2001, pbmclean accepted -N instead of -minneighbors.
The default for N is 1 - only completely isolated pixels are flipped.
(A value of N 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).
You can use pbmclean to clean up "snow" on bitmap images.
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