Digital video bit rate reduction: Blanking elimination for sub-Nyquist (2f sub sc) PAL

British Telecom is converting its communications network to digital operation, and the analogue circuits will eventually disappear. Although video signals can easily be converted to digital form, the bit rate occupied by a conventional pulse-code modulation (p.c.m.) video signal is high. Economies in the use of circuits could be made by reducing this bit rate. The elimination of blanking intervals from the digitized signal, which is one of several techniques investigated as a means of reducing bit rates is discussed. It is concluded that blanking elimination, although possible, is unattractive for PAL-code signals because of the complexity of the equipment. However, for signals that are more tightly defined, for example those complying with the CCIR recommendations for the digital coding of component video signals, blanking elimination would be a straightforward process that could be used with confidence to provide a valuable saving of bit rate with no impairment to picture quality.