pnmnorm — Normalize the contrast in a PNM image. See also: `pnmhisteq`. More information: <https://netpbm.sour

Force the brightest pixels to be white, the darkest pixels to be black and spread out the ones in between linearly

pnmnorm {{path/to/image.pnm}} > {{path/to/output.pnm}}

Force the brightest pixels to be white, the darkest pixels to be black and spread out the ones in between quadratically such that pixels with a brightness of `n` become 50 % bright

pnmnorm {{[-midv|-midvalue]}} {{n}} {{path/to/image.pnm}} > {{path/to/output.pnm}}

Keep the pixels' hue, only modify the brightness

pnmnorm {{[-k|-keephues]}} {{path/to/image.pnm}} > {{path/to/output.pnm}}

Specify a method to calculate a pixel's brightness

pnmnorm -{{luminosity|colorvalue|saturation}} {{path/to/image.pnm}} > {{path/to/output.pnm}}