| 摘要 |
PURPOSE:To control contrast and to suppress variance between R, G and B (red, green and blue) signals by controlling a contrast control circuit by YM signals that has an inverted level in the superimposing display area from that in the other area. CONSTITUTION:When there is no YM signal that has an inverted level in the superimposing display area from that in the other area, a Y voltage conversion circuit 21 is at the H level to cut off the transistor 20. The input YM signal causes a voltage to be output to the base terminal of the transistor 20. Actuated transistor 20 causes a current to flow through resistors 18 and 19 for feeding the input voltage to the contrast control voltage generating circuit 15 has a fixed voltage. When the voltage determined by the volume control 17 is lower than the output voltage of the YM voltage conversion circuit 21, the transistor 20 is left cut off, and therefore, a luminance Y signal output to the output device 14 is not influenced by the YM signal. That is, when the contrast is high, signal 24 but not 23 shown in figure is output and serves as the Y signal. |
