DIGITAL VIDEO: differential coding of PAL signals based on differences between samples one subcarrier period apart

摘要

Methods for reducing the bit-rate required for digital coding of System I (PAL 625-line) video signals by means of differential pulse code modulation are discussed The subjective effect of various d.p.cm. and hybrid d.p.cm./p.c.m. coding systems have been investigated with a view to finding a system giving broadcast quality pictures. All the systems examined would require the transmission of either five or six bits per sample at a sampling frequency which is thrice the PAL colour subcarrier frequency, Le. 13-3 MHz. The d/p.cm. codes used in most experiments indicate the change in level between every third sample of the video signal, but the possibility of conditional operation using adjacent samples was also examined.nThe results of subjective tests indicated that for a single coding and decoding operation, broadcast quality pictures can be obtained using five bits per sample. In practice, however, up to two extra bits would probably be required per sample to allow for several coders and decoders in tandem and for error protection.