Keynote Speech 

Just Noticeable Differences—Optimizing the Perceptual Quality of Real-Time Multimedia Systems over the Internet

Benjamin W. Wah, The Chinese University of Hong Kong, Hong Kong

Just-noticeable difference (JND) refers to the smallest detectable difference between a starting and a secondary level of a particular sensory stimulus. It was first pioneered by Ernst Weber, a 19th century experimental psychologist. Weber’s Law simply states that the size of JND is a constant proportion of the original stimulus value. Although the concept is known for over one and a half centuries, it has recently received more attention in the multimedia community. With the quality degradations incurred by losses and delays in transferring multimedia signals over the Internet, researchers have found that existing quantitative metrics cannot model perceptual degradations experienced by users. In this presentation, we examine the limitations of current results on JND and the reasons why they are inadequate for improving the perceptual quality of multimedia systems. Features that contribute to the complications include the presence of multiple and possibly dependent stimuli that may be related to perceptual quality in a linear or nonlinear fashion and whose effects may be additive or non-additive. Based on JND, we present new methods for conducting subjective tests in order to optimize the perceptual quality of real-time multimedia systems over the Internet. We further illustrate their effects on JND using various applications in online games, video conferencing, video coding, and remote control. The understanding of the properties of JND with multidimensional stimuli will help reduce the number of subjective tests needed in designing better QoE-based control and optimization in multimedia algorithms.


Benjamin W. Wah is currently the Provost and Wei Lun Professor of Computer Science and Engineering of the Chinese University of Hong Kong. Before then, he served as the Director of the Advanced Digital Sciences Center in Singapore, as well as the Franklin W. Woeltge Endowed Professor of Electrical and Computer Engineering and Professor of the Coordinated Science Laboratory of the University of Illinois, Urbana-Champaign, USA. He received his Ph.D. degree in computer science from the University of California, Berkeley, CA, in 1979. He had served on the faculty of Purdue University. He has received a number of awards for his research contributions, which include the IEEE CS Technical Achievement Award (1998), the IEEE Millennium Medal (2000), the Society for Design and Process Science Raymond T. Yeh Lifetime Achievement Award (2003), the IEEE-CS W. Wallace-McDowell Award (2006), the Pan Wen-Yuan Outstanding Research Award (2006), the IEEE-CS Richard E. Merwin Award (2007), the IEEE-CS Technical Committee on Distributed Processing Outstanding Achievement Award (2007), the IEEE-CS Tsutomu Kanai Award (2009), and the Distinguished Alumni Award in Computer Science of the University of California, Berkeley (2011). Wah's current research interests are in the areas of nonlinear search and optimization, multimedia signal processing, and computer networks.

Wah cofounded the IEEE Transactions on Knowledge and Data Engineering in 1988 and served as its Editor-in-Chief between 1993 and 1996, and is the Honorary Editor-in-Chief of Knowledge and Information Systems. He currently serves on the editorial boards of Information Sciences, International Journal on Artificial Intelligence Tools, Journal of VLSI Signal Processing, and World Wide Web. He has served the IEEE Computer Society in various capacities, including Vice President for Publications (1998 and 1999) and President (2001). He is a Fellow of the AAAS, ACM, and IEEE.


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