1. Electronic Engineering, Tsinghua University, 12442 Beijing, Beijing, China, 100084 (e-mail: qinzy@mit.edu)
2. Media Computing, Microsoft Research Asia, 216064 Beijing, Beijing, China, (e-mail: jinglu.cs@gmail.com)
3. Internet Media Group, Microsoft Research Asia, Bejing, Beijing, China, 100191 (e-mail: yanlu@microsoft.com)