1. Department of Computer Science and Technology, Tsinghua University, Beijing, China
2. Department of Computer Vision Technology (VIS), Baidu Inc., Beijing, China
3. Department of Computer Science, University of Minnesota Duluth, Duluth, MN, USA
4. School of Artificial Intelligence, OPtics and ElectroNics (iOPEN), Northwestern Polytechnical University, Xi’an, China
5. Department of Computing, The Hong Kong Polytechnic University, Hung Hom, Hong Kong