References
 J. Koplowitz and G. T. Toussaint, "A Unified Theory of Coding Schemes for the Efficient Transmission of Line Drawings", Proceedings of IEEE Conference on Communications and Power, Montreal, October 1976, pp. 205208.
 H. Freeman, "On the Encoding of Arbitrary Geometric Configurations," IRE Trans. Electronic Computers, Vol. EC10, pp. 260268, June 1961.
