CmdID / Commands
ppmdist
Produce a grayscale version of a PPM image. tldr-pages
On several platforms
Produce a grayscale version of the specified PPM image
ppmdist path/to/input.ppm >path/to/output.pgmIdentify
Use the specified method to map colors to graylevels
ppmdist -frequency path/to/input.ppm >path/to/output.pgmIdentify