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Why do we need compression?

The high bit rates that result from the various types of digital video make their transmission through their intended channels very difficult. Even entertainment video with modest frame rates and dimensions would require bandwidth and storage space far in excess of that available from CD-ROM. Thus delivering consumer quality video on compact disc would be impossible. This is analagous to an envelope being to large to fit into a letterbox. Similarly the data transfer rate required by a video telephony system is far greater than the bandwidth available over the plain old telephone system (POTS). Even if high bandwidth technology (e.g. fibre-optic cable) was in place, the per-byte-cost of transmission would have to be very low before it would be feasible to use it for the staggering amounts of data required by HDTV. Finally, even if the storage and transportation problems of digital video were overcome, the processing power needed to manage such volumes of data would make the receiver hardware very expensive.

Although significant gains in storage, transmission, and processor technology have been achieved in recent years, it is primarily the reduction of the amount of data that needs to be stored, transmitted, and processed that has made widespread use of digital video a possibility. This reduction of bandwidth has been made possible by advances in compression technology. Advances in compression techology more than anything else have led to the arrival of video to the desktop and hundreds of channles to the home.

Compression reduces the bandwidth required to transmit and store digital video. So what is compression, and how does it work?

© Colin E. Manning 1996