| 摘要 |
An index signal (1D) is provided which determines a given period (T), say sixty seconds of the television signal for a program to be scrambled. The scene changes in the period are detected and signalled (Sc). A key signal pattern (P1) for the given period is produced, of which the leading and trailing edges are arranged for coincidence with the field period. The index signal, scene change signal and key signal pattern are used to derive a scrambling pattern (P2-P4) which controls the timing of the inversion of the polarity of the transmitted television signal. The period of the scrambling pattern is equal to the given period. The patterns (P2-P4) are produced by logic operations on the signals 1D, Sc and P1, e.g. pattern P2 is derived by logical NAND on these signals.
|
