ppmdist

Produce a grayscale version of a PPM image. More information: https://netpbm.sourceforge.net/doc/ppmdist.html.

• Produce a grayscale version of the specified PPM image:

ppmdist path/to/input.ppm > path/to/output.pgm

• Use the specified method to map colors to graylevels:

ppmdist -frequency|intensity path/to/input.ppm > path/to/output.pgm