Source of ColorQuantization/Octree

- Color quantization using octrees
--   http://www.leptonica.org/papers/colorquant.pdf


- A Simple Method for Color Quantization: Octree Quantization
--  https://link.springer.com/chapter/10.1007/978-3-642-83492-9_20

- Octree Color Quantization
--  https://www.cubic.org/docs/octree.htm

- https://www.codeproject.com/Articles/109133/Octree-Color-Palette