pbmreduce

Proportionally reduce a PBM image. See also: pamenlarge, pamditherbw. More information: https://netpbm.sourceforge.net/doc/pbmreduce.html.

pbmreduce N path/to/image.pbm > path/to/output.pbm

pbmreduce -threshold N path/to/image.pbm > path/to/output.pbm

pbmreduce -value 0.6 N path/to/image.pbm > path/to/output.pbm