ppmdither

Reduce the number of colors in an image by applying dithering. More information: https://netpbm.sourceforge.net/doc/ppmdither.html.

• Read a PPM image, apply dithering and save it to a file:

ppmdither path/to/image.ppm > path/to/file.ppm

• Specify the desired number of shades for each primary color:

ppmdither -red 2 -green 3 -blue 2 path/to/image.ppm > path/to/file.ppm

• Specify the dimensions of the dithering matrix:

ppmdither -dim 2 path/to/image.ppm > path/to/file.ppm