 of Computing and Electronic Systems at the University of Essex. His extensive research interests include telecommunications, renewable energy, and domestic appliance control, although his principal area of interest is video and image coding, where he is widely published. Having gained a Ph.D. in model- based image coding in 2000, John is one of the leaders in the field of object-based image coding and segmentation. This page intentionally left blank Part 1 For most of the past century, the main purpose of telecommunications networks has been to enable voice communications between people at a distance. To a lesser extent it has included communications between people and voice recording or playback devices, such as automatic voice response systems. In more recent decades, there has also been a steady growth in the use of telecommunications networks to provide data connections for applications such as remote sensing, transfering data between data centers, or carrying TV signals in digital format. However, more recently, the emphasis has shifted very much toward the provision of connections between information systems or between people and information systems capable of carrying voice, video, or data signals. Voice and video signals are analogue at their source and in early systems were transported over telecommunications networks in analogue form. With the relent- less development of digital technology, however, analogue systems have progres- sively given way to digital transmission, with signals remaining in analogue format for only a short distance before being converted to digital. Data signals, on the other hand, often start out in digital format-for example, from a file or data storage device. Digital signals generally need more bandwidth for their transmission than analogue ones, but they offer the advantage (with careful systems design) of being highly resistant to noise and other impairments and of being highly extendable. In recent years considerable emphasis has been placed on ways to reduce the bit- rate