1. On the encoding of arbitrary geometric configurations;Freeman;IRE Trans. Electron. Comput.,1961
2. Computer recognition of partial views of curved objects;Mckee;IEEE Trans. Comput.,1977
3. M.D. Levine, Vision in Man and Machine, McGraw-Hill Publishing Company, printed in the USA, 1985.
4. Computer processing of line drawing images;Freeman;Comput. Surv.,1974
5. F. Kuhl, Classification and recognition of hand-printed characters, IEEE International Convention Record, Pt. 4, 1963, pp. 75–93.