Overview

Digital video compression techniques have played an important role in the world of telecommunication and multimedia systems where bandwidth is still a valuable commodity. Hence, video coding techniques are of prime importance for reducing the amount of information needed for a picture sequence without losing much of its quality, judged by the human viewers. Modern compression techniques involve very complex electronic circuits and the cost of these can only be kept to an acceptable level by high volume production of LSI chips. Standardisation of the video compression techniques is therefore essential.

An analogue videophone system had been tried out in the 1960s, but it required a wide bandwidth and the postcard-size black-and-white pictures produced did not add appreciably to the voice communication. In the 1970s, it was realised that visual speaker identification could substantially improve a multiparty discussion and videoconference services were considered. Interest increased with improvements in picture quality and digital coding. With the available technology in the 1980s, COST211 video codec, based on Differential Pulse Code Modulation (DPCM) was standardised by CCITT, under the H.120 standard. The codec's target bit rate was at 2 Mbit/s for Europe and 1.544 Mbit/s for North America, suitable for their respective first levels of digital hierarchy. However, the image quality, although having very good spatial resolution (due to the nature of DPCM working on pixel-by-pixel bases), had a very poor temporal quality. It was soon realised that in order to improve the image quality, without exceeding the target bit rate, less...