Digital video: sub-Nyquist sampling of Pal colour signals

The use of sub-Nyquist sampling frequencies for coding monochrome video signals or the separate components of colour signal is well known as a means of reducing bit rates. However, such techniques are usually unsatisfactory for coding composite colour signals. This paper describes a technique which may be used for composite Pal signals in which a sub-Nyquist sampling frequency equal to twice the colour subcarrier frequency is used in conjunction with comb filtering. Both analogue and digital realisations of the necessary filters are described, and consideration is given to the multiple use of the technique in cascaded links. Results are given of a subjective assessment of the technique, compared with super-Nyquist sampling, when used in conjunction with pulse-code modulation p.c.m. and differential p.c.m.