Generate a grayscale ramp
pgmramp -lr|-tb | -rectangle|-ellipse width height
Generates a graymap of the specified size containing a black-to-white ramp. These ramps are useful for multiplying with other images, using the pnmarith tool.
-lr
A left to right ramp.
-tb
A top to bottom ramp.
-rectangle
A rectangular ramp.
-ellipse
An elliptical ramp.
All flags can be abbreviated to their shortest unique prefix.
Copyright (C) 1989 by Jef Poskanzer.