ABSTRACT
Compression, data reduction or bit-rate reduction, is the technique of filtering out some of the information that is contained in a digital video signal. By eliminating selected data, the signal can be passed through a channel that has a lower bit rate. The ratio between the source and the channel bit rates is called the compression factor. At the receiving end of the channel an expander or decoder will attempt to restore the compressed signal to near its original range of values. A compressor is designed to recognize and pass on the useful part of the input signal known as the entropy. The remaining part of the input signal is called the redundancy. It is redundant because the filtered-out information can be predicted from what has already been received by the decoder. If the decoder cannot reconstruct the withheld data, then the signal is incomplete and the compression has degraded the original signal. This may or may not be acceptable when viewing the received image.
