1. College of Computer Science, Nankai University, Tianjin, China
2. College of Electronic Science and Technology, National University of Defense Technology, Changsha, China
3. College of Computer, National University of Defense Technology, Changsha, China
4. Center for Machine Vision and Signal Analysis (CMVS), University of Oulu, Oulu, Finland
5. TKLNDST, College of Computer Science, Nankai University, Tianjin, China