Overview

The JPEG standard for coding of digital images, designed by the Joint Photographic Experts Group, is in fact a product of a collaborative effort between ITU-T and ISO (International Standards Organisation) [1]. It aims to support a wide variety of applications for compression of continuous-tone images and is the most frequently used means of compressing still images. It can code full colour images, achieving an average compression ratio of 15:1 for subjectively transparent quality [2]. Its design meets special constraints, which make the standard very flexible. For example, the JPEG encoder is parametrisable, so that the desired compression/quality trade-offs can be determined based on the application or the wishes of the user [3]. Other examples of applications that JPEG algorithm supports include Adobe's PostScript language for printing systems, the Raster Content portion of the ISO Office Document Architecture and Interchange format, the future ITU-T colour facsimile standard and European ETSI videotext standard [1].

JPEG can also be used in coding of video, on the basis that video is a succession of still images. In this case the process is called Motion JPEG. Currently, Motion JPEG has found numerous applications. The most notable one is video coding for transmission over packet networks with unspecified bandwidth or bit rates (UBR). A good example of UBR networks is the Internet, where, due to unpredictability of the network load, congestion may last for a significant amount of time. Since in Motion JPEG, each frame is independently coded, it is an ideal encoder...