| 摘要 |
PURPOSE:To prevent a picture from getting adverse by operating an automatic black level adjusting circuit by adjusting the level of a vertical sawtooth wave signal so as to project a bright line for reference out of an effective picture when projecting the picture of an aspect ratio laterally longer than a screen aspect ratio. CONSTITUTION:When projecting the picture of an aspect ratio 16:9 with a screen aspect ratio 4:3, first and second changeover switches SW1 and SW2 are switched to the side of a terminal (b). Then, a vertical sawtooth wave generating circuit 2 outputs the vertical sawtooth wave signal of an amplitude smaller than the case of projecting the picture of 4:3, and the shift pulse of a pulse preparing circuit 8 is added to this signal. Therefore, the almost vertical sawtooth wave signal is supplied to a vertical output circuit 3, and the picture of 16:9 is projected. A reference pulse is inserted to the video signal by the black level adjusting circuit and this reference pulse block is coincident with a shift pulse block, the bright line for reference is positioned out of the effective picture. |
