chapter  1
34 Pages

Introduction to compression

MPEG is actually an acronym for the Moving Pictures Experts Group

which was formed by the ISO (International Standards Organization) to

set standards for audio and video compression and transmission.

Compression is summarized in Figure 1.1. It will be seen in (a) that the

data rate is reduced at source by the compressor. The compressed data are

then passed through a communication channel and returned to the

original rate by the expander. The ratio between the source data rate and

the channel data rate is called the compression factor. The term coding gain

is also used. Sometimes a compressor and expander in series are referred

to as a compander. The compressor may equally well be referred to as a

coder and the expander a decoder in which case the tandem pair may be

called a codec.