1. School of Communications and Information Engineering, Chongqing University of Posts and Telecommunications, Chongqing, China
2. Chongqing Key Laboratory of Computational Intelligence, Chongqing University of Posts and Telecommunications, Chongqing, China
3. Chongqing Key Laboratory of Image Cognition, Chongqing University of Posts and Telecommunications, Chongqing, China
4. Department of Informatics, University of Oslo, Oslo, Norway