| 摘要 |
PURPOSE:To perform the control of the reference level in the station at a high speed and a simple and accurate way without using any measuring instrument, by projecting pictures simultaneously on the same screen and on the basis of the reference level. CONSTITUTION:The video-amplified TV signal is supplied to a terminal 1 and then fed to a pedestal clamping circuit 2 via a transistor (TR) Q1. For the circuit 2, a TR Q2 is turned on by the clamp pulse given from a terminal 3 and the pedestal level is clamped to the level set by a volume 4. The clamped TV signal is supplied to a video output circuit 6 via the TR Q2, and the output of the circuit 6 is applied to an anode of a CRT to reproduce a prescribed video. A video switching circuit 7 is switched alternately by the switching pulse PAC, and a black level picture 11A corresponding to a period T1 of the test signal ST is projected at the center on a screen during a period T1. At the samd time, a picture 11B which is based on the reference signal SB of the set side is projected on other screens. Therefore the volume 4 is controlled so as to obtain an equal level of brightness between the pictures 11A and 11B. |
