pbmmake - create a blank bitmap of a specified size
Produces a portable bitmap of the specified width and
height. The color defaults to white.
In addition to the usual -white and -black,
this program implements -gray. This gives a simple
50% gray pattern with 1's and 0's alternating.
All flags can be abbreviated to their shortest unique
Copyright (C) 1989 by Jef Poskanzer.