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.
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.
Options let you choose the shape of the ramp (left to right, inside out, etc.). You can use pamflip to get more shapes. For example, the -lr option gives you a left to right ramp and
$ pgmramp -lr 100 100 | pamflip -lrgives you a right to left ramp.
To generate a simple ramp of all the values from 0 to maxval, and not necessarily a graphic image, use pamseq.
ppmrainbow does something similar to what pgmramp does, but for color. The image fades between two colors of your choice.
This option was new in Netpbm 10.66 (March 2014).
This option was new in Netpbm 10.1 (June 2002). Before that, the maxval is always 255.