CIRCUITS SYSTEMS SIGNAL PROCESSING VOL. 20, NO. 3, 2001, PP. 415–445 O N THE I MPORTANCE OF E RROR R ESILIENCE IN V ISUAL C OMMUNICATIONS OVER N OISY C HANNELS * Andrew Perkis 1 Abstract. This paper presents the importance of error resilience tools in visual com- munications. Error resilience tools provide a mechanism enabling transmission of visual information over channels with residual random bit errors in the received bit stream. The benefits of using error resilience tools are proven by devising the analytic relationship between the time delay in a transparent channel using Automatic Repeat Request and the Author: OK? equivalent residual bit error rate in a nontransparent channel. The error resilience tools make it possible to achieve an acceptable visual quality even in the presence of these residual errors. Our work is related and compared to the standardization work of the next- generation still image compression system JPEG2000. The results show that partial and complete substitution of the quantization and symbol encoding in visual compression systems by robust error resilience tools provides a signif- icant increase in robustness. Three error resilience tools are discussed: (1) substitution of the quantization and symbol encoding by a fixed length coding scheme, (2) substitution by a mixed fixed length coding and variable length coding scheme, and (3) substitution of the variable length coding by reversible variable length coding. Key words: Image compression systems, error resilience, multimedia communications. 1. Introduction All people rely on some form of communication, i.e., messages carried through a channel in some way. A large part of this communication is carried out using our voices or visual information. The fundamental study of communications and the characteristics thereof, including the study of the signal characteristics themselves, traditionally belongs to the field of psychology, linguistics, or acous- tics, and to some extent sociology. The engineering or technical aspect of all ∗ Received March 1, 2000; revised September 1, 2000. 1 Norwegian University of Science and Technology, Department of Telecommunications, 7491 Trondheim, Norway. E-mail: andrew@tele.ntnu.no