compress vb.: to squeeze together or compact into less space; condense
compression noun: the act of compression or the condition of being compressed
Compression is the act or process of compacting data into a smaller number of bits. Video compression (video coding) is the process of converting digital video into a format suitable for transmission or storage, whilst typically reducing the number of bits. 'Raw' or uncompressed digital video typically requires a large bitrate, approximately 216Mbits for 1 second of uncompressed Standard Definition video, see Chapter 2, and compression is necessary for practical storage and transmission of digital video.
Compression involves a complementary pair of systems, a compressor (encoder) and a decompressor (decoder). The encoder converts the source data into a compressed form occupying a reduced number of bits, prior to transmission or storage, and the decoder converts the compressed form back into a representation of the original video data. The encoder/decoder pair is often described as a CODEC (enCOder/DECoder) (Figure 3.1).
Data compression is achieved by removing redundancy, i.e. components that are not necessary for faithful reproduction of the data. Many types of data contain statistical redundancy and can be effectively compressed using lossless compression, so that the reconstructed data at the output of the decoder is a perfect copy of the original data. Unfortunately, lossless compression ...