pnmhisteq — Histogram-equalize a PNM image. More information: <https://netpbm.sourceforge.net/doc/pnmhisteq.html

Increase the contrast of a PNM image using histogram equalization

pnmhisteq {{path/to/input.pnm}} > {{path/to/output.pnm}}

Only modify grey pixels

pnmhisteq {{[-g|-grey]}} {{path/to/input.pnm}} > {{path/to/output.pnm}}

Do not include black or white pixels in the histogram equalization

pnmhisteq -no{{black|white}} {{path/to/input.pnm}} > {{path/to/output.pnm}}