X. Wang, G. Shi, and J. Yang. Proceedings of the 2009 10th International Conference on Document Analysis and Recognition, page 1056--1060. Washington, DC, USA, IEEE Computer Society, (2009)
K. Takeda, G. Earl, J. Frey, S. Keay, and A. Wade. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, (2013)