pnmmargin • man page

pnmmargin - add a border to a portable anymap

pnmmargin [-white|-black|-color colorspec] size [pnmfile]

Reads a portable anymap as input. Adds a border of the specified number of pixels, and produces a portable anymap as output.

You can specify the border color with the -white, -black, and -color flags. If no color is specified, the program makes a guess.

It's a script. Scripts are not portable to non-Unix environments.