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}}