| 摘要 |
PURPOSE:To reduce flickers arising when an encoded video signal is decoded and to prevent the deterioration of a reproduced and restored video by permitting the prescribed horizontal synchronizing signal to generate a DC voltage off-set in accordance with video secret information and transmitting a transmission video signal available from inverting a video signal at the prescribed level specified by the video secret information during a horizontal period. CONSTITUTION:As the cipher processing with respect to the video signal generated in a video signal generating circuit 20, a broadcasting station 300 side inverts the video signal at random, superimposes the random horizontal synchronizing signal with a DC voltage and executes the synchronizing signal off-set. After a subscriber terminal 400 converts a signal received by a tuner T1 into a base band frequency, it detects the video. A data extracting circuit 32 extracts transmitted data which is superimposed during the vertical blanking interval of the video signal, and a data reproducing circuit 34 reproduces said data. A pedestal reproducing circuit 35 reproduces the off-set voltage with respect to the synchronizing signal and applies it to a synchronizing off-set circuit 36. The DC level detected by the pedestal reproducing circuit 35 is also used for deciding the DC level when the video signal whose polarity is inverted is restored by a video inverting circuit 37. |
