GB1313832A - Reduction of errors in television signals - Google Patents

Abstract

1313832 Selective signalling BRITISH BROADCASTING CORP 20 Jan 1972 [1 Feb 1971] 3618/71 Heading G4H [Also in Division H4] To reduce the apparent effect of errors in a digital television signal which includes a first video signal (e.g. luminance signal), and a second video signal (e.g. a chrominance signal) modulated on to a subcarrier (e.g. digital PAL or NTSC colour television signal), and wherein the sampling frequency of the digital signal is equal to n times the subcarrier frequency (n being an integer greater than one), each word of the digital signal is stored for at least n words and when an error is detected in a word, this word is replaced by the word which is n words earlier. Thus the incorrect word is replaced by an alternative one which was derived from a video sample taken in the same relative position on the previous cycle of the chrominance subcarrier. In the embodiment described the storage means comprises n storage units 11, 12 and 13 (n = 3) each of which holds the word (eight bit word) applied thereto until supplied with a new word. The storage units are sequentially 16 clocked by clock pulses from input 14 unless an incorrect word is detected by a parity check in unit 20 which results in gate 15 for the clock pulses being inhibited and the incorrect word not being stored. Selector switch 17 which sequentially connects the storage units to the output 18 operates in synchronism with switch 16.