nverse
   function to colormap removal; namely, color quantization
   from 24 bpp full color to 8 bpp colormap with some number
   of colormap colors.  Several versions are provided, some that
   use a fast octree vector quantizer and others that use
   a variation of the median cut quantizer.  For high-level interfaces,
   see for example: pixConvertRGBToColormap(), pixOctreeColorQuant(),
   pixOctreeQuantByPopulation(), pixFixedOctcubeQuant256(),
   and pixMedianCutQuant().

11. Programmatic image display