1. Department of Computer Science and Information Engineering, National Taiwan University, Taipei, Taiwan
2. Department of Computer Science and Information Engineering, National Taiwan University, Institute of Information Science, Academia Sinica, Taipei, Taiwan
3. Institute of Information Science, Academia Sinica, Taipei, Taiwan
4. Department of Computer Science and Information Engineering, National Taiwan University, Taipei, Taiwan College of Engineering, City University of Hong Kong Kowloon, Hong Kong