pgmramp - generate a grayscale ramp
pgmramp -lr|-tb|-rectangle|-ellipse -maxval=maxval width height
All options can be abbreviated to their shortest unique prefix. You may use two hyphens instead of one to designate an option. You may use either white space or an equals sign between an option name and its value.
This program is part of Netpbm(1).
Generates a graymap of the specified size containing a black-to-white ramp. These ramps are useful for multiplying with other images, using pamarith.
The ramp is linear in brightness, not intensity. I.e. the gamma-corrected sample values in the PGM rise linearly with distance from the corner of the image. If you want a ramp that is linear in light intensity, use pnmgamma with pgmramp.
To generate a simple ramp of all the values from 0 to maxval, and not necessarily a graphic image, use pamseq(1).
ppmrainbow does something similar to what pgmramp does, but for color. The image fades between two colors of your choice.
You must specify exactly one of the ramp type options.
This option did not exist before June 2002. Before, the maxval was
Copyright (C) 1989 by Jef Poskanzer.