1. Research Center of Machine Vision Engineering of Hebei Province, Key Laboratory of Digital Medical Engineering of Hebei Province, College of Electron and Information Engineering, Hebei University, Baoding 071002, P. R. China
2. Electrical and Computer Engineering Department, Southern Illinois University Carbondale, Carbondale, Illinois 62901, USA
3. Department of Materials Science and Engineering, National University of Singapore, Singapore 117576, Singapore