pnmnorm

Normalize the contrast in a PNM image. See also: pnmhisteq. More information: https://netpbm.sourceforge.net/doc/pnmnorm.html.

• 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 -midvalue n path/to/image.pnm > path/to/output.pnm

• Keep the pixels’ hue, only modify the brightness:

pnmnorm -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