| 摘要 |
PURPOSE:To make the black level constant to even a signal whose pedestal level is changed by a mean brightness level and to make the output signal level constant even when the DC sending quantity is changed by providing two level shift circuits whose level shift quantity is changed depending on the black level detection signal. CONSTITUTION:A pedestal clamp circuit 4 and a level shift circuit 11 connect to an output of a DC transmission quantity setting circuit 3 and other level shift circuit 12 is connected to the input of the circuit 3. The output of the circuit 11 is inputted to the black level detection circuit 10. The circuit 10 detects a black level of a darker input signal than the black level setting level 7, smoothes the detection signal and outputs it to the level shift circuits 11,12. The output of the circuit 11 is subject to negative feedback so that the black peak level is equal to the black level setting level 7 to correct the black level and the pedestal level is changed by the means brightness level. Since the output of the amplifier circuit 2 is connected to the circuit 12, the similar black level correction is applied also to the output of the circuit 2 and the result is outputted from a terminal 13. |
