GB1457452A - Television signals - Google Patents

Abstract

1457452 Television BRITISH BROADCASTING CORP 25 Nov 1974 [23 Nov 1973] 54493/73 Heading H4F A television signal in digital form is modified to include an error protection (i.e. parity) bit for each digital word (e.g. for each eight-bit word representing a picture sample), and selected bits (e.g. the parity bits or the least significant bit of each word) are inserted into at least some of the blanking intervals in the signal (e.g. into the horizontal blanking intervals). In this way the parity bits are added to the television signal without increasing the gross bit rate. Preferably the line sync. pulse and colour burst in the blanking intervals are removed before the selected bits are inserted, although the selected bits may be inserted at the times marked P in Fig. 2, i.e. during the stationary levels of the line blanking period. The bits of the television signal are delayed in line store 12 by approximately one line period relative to the error protection (parity) bits associated with that line before being applied to a transmission or processing channel 22, the 704 parity bits for the 704 eight-bit words being formed into 88 eight-bit words in store 13. Each parity bit is formed in generator 11 by the resultant of adding modulo-2 all or at least the more significant of the bits of the associated eight-bit word. The line store 12 may be situated at the receiver between switch 15 and error protection check circuit 18. If transmission is as in Fig. 2 then a D-A converter 20 may be connected to feed a colour decoder and monitor 21.