| 摘要 |
PURPOSE:To attain a complete concealing effect by a simple construction and provide a picture of high quality by superimposing a concealing signal having the concealing information applied to plural frequency signals of different combinations on a horizontal or a vertical synchronizing signal of a video signal. CONSTITUTION:IN a transmitting side, a vertical or a horizontal synchronizing period in a video signal is extracted by a synchronizing extracting section 2, a timing Ts for inserting subcarriers 13, 14 is ciphered and the subcarrier is AM or FM modulated to transmit the information relating to the encipherment. During a synchronizing period, the AM or FM modulated subcarriers 13, 14 are superimposed at the timing according to a predetermined cipher code and transmitted. After the cipher code is decoded in a receiver side, a wave form having the same frequency, the same phase and the same amplitude as the subcarriers 13, 14 is reproduced as an output of a synchronous extracting section 9. This signal is subtracted from a receiving signal at a subtracting point to obtain a video signal having no distortion nor interference. |
