1. College of Computer Science and Electronic Engineering, Hunan University, Changsha, China
2. School of Robotics and the National Engineering Research Center of Robot Visual Perception and Control Technology, Hunan University, Changsha, China
3. Karlsruhe Institute of Technology, Karlsruhe, Germany
4. College of Electrical and Information Engineering and the Key Laboratory of Visual Perception and Artificial Intelligence of Hunan Province, Hunan University, Changsha, China