pnmnorm
Normalize the contrast in a PNM image. tldr-pages
On several platforms
Several platforms
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.pnmIdentifyForce 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 -midvalue n path/to/image.pnm >path/to/output.pnmIdentifyKeep the pixels' hue, only modify the brightness
pnmnorm -keephues path/to/image.pnm >path/to/output.pnmIdentifySpecify a method to calculate a pixel's brightness
pnmnorm -luminosity path/to/image.pnm >path/to/output.pnmIdentify