Variable-Length Redundancy Removal Coders for Differentially Coded Video Telephone Signals

A study of the statistics of a differential pulse-code modulation coder for Picturephone® signals which uses a three-bit uniform length code suggests that a higher transmission efficiency can be obtained with a variable word length code. This permits an increase in number of quantizing levels used, thus improving picture quality. A quantizer with 24 levels rather than eight can be used provided that a buffer store of 10 000 bits is included in the system to smooth the irregular data flow caused by the varying code word length.