| 摘要 |
PURPOSE:To simplify the constitution of a device, by modulating a background color video signal with a control signal gated with a key signal band-limited and being the luminance signal of a foreground signal. CONSTITUTION:An output S1 is obtained by detecting a chrominance carrier signal of the foreground 3 with a detection axis of blue. The output S1 is sliced and a key pulse S2 having a fall in coincidence with the boundary between a screen 1 and an objective 2 is formed. The pulse S2 is band-limited and a key signal S3 having a tilt in the width of TE from the boundary is generated. A luminance signal S4 appears from a trap 13 and is gated with the signal S3, and a control signal S5 for modulation is formed. An output S6 of a circuit 23 indicates the foreground signal. A background signal S7 is modulated with the signal S5, the gain is made to 1 at a section corresponding to the screen 1 of the signal S5, and a signal S8 in which the gain is reduced with the signal S5 increased more, is obtaind. A delay circuit 24 forms a key signal S9 where an edge exists around the center of the period TE and the signal synthesizes the signals S6 and S3. |
