| 摘要 |
PURPOSE:To keep the video quality in excellent manner, by following the threshold level to an optimum level quickly, against the change in the background density and contrast in the original, in a background density compensation circuit provided at a facsimile transmitter and the like. CONSTITUTION:An analog video signal is sample-held and given to a white peak value detection circuit 2' and another circuit 17. The time constant consisting of a capacitor 25 and a resistor 26 of the circuit 17 is sufficiently greater than that consisting of a capacitor 8 and a resistor 9. An output voltage V of the circuit 17 is split with registors 18, 19, 20, and a voltage division VH is given to one end of the registor 9 and a voltage division VL is given to one end of a resistor 14 of a circuit 3'. Thus, even if white or black signals are consecutively present (i.e., black or white signals are absent), since the threshold value is existing between the peak value voltage VSH or VSL or consecutive chroma signals and the voltage division VH or VL, accurate binarization can be made. |
