PURPOSE: To obtain the higher scramble effect and to obtain higher secrecy by level-shifting the horzontal blanking period in the whole period of a signal, and by inverting an optional image part by the prescribed folding back level.
CONSTITUTION: A signal S0 which is supplied from a video signal source 1 is added to an HBLK shift circuit 3 through an amplifier 2, and is also added to a synchronizing separator circuit 4. As a result, horizontal and vertical synchronizing signals are separated. A timing circuit 5 controls the operational timing of the circuit 3 based on the signal from the circuit 4, and the level shift of the horizontal blanking period is executed over the whole period of the signal S0. A level-shifted signal S1 is added to an inversion/noninversion circuit 6, and the volantary horizontal blanking period and/or the volantary image part are/is inverted by a 50IRE intermediate luminance level.
HIRAYASU KATSUTOSHI
NAKAMICHI YUKIYA