pnmmargin

Add a border to a PNM image. More information: https://netpbm.sourceforge.net/doc/pnmmargin.html.

• Add a border of the specified size to a PNM image:

pnmmargin size path/to/image.pnm > path/to/output.pnm

• Specify the color of the border:

pnmmargin -color color size path/to/image.pnm > path/to/output.pnm