| 摘要 |
PURPOSE:To perform correct binary coding by detecting the maximum and minimum points of an analog picture signal, varying the white and black peak-held value of the analog picture signal to the current maximum and minimum voltages forcibly, and coding the analog picture signal into a binary signal on the basis of the mean value of both held values as a threshold value. CONSTITUTION:The analog picture signal is inputted from a terminal 60 and capacitors 70 and 71 are charged to a positive or negative peak value. When the signal does not have the peak value, the capacitors are discharged with time constant determined by resistances 73 and 71. When a peak phase detecting circuit 61 detects the maximum point, a transistor (TR) 66 is turned on to vary the value of the capacitor 70 to the current maximum value of the analog picture signal focibly. For the minimum point, a TR67 functions similarly. Consequently, the potentials of the capacitors 70 and 71 approximate a maximum and a minimum envelope potential and the plus input side of a comparator 77 approximates the mean value of the picture signal, thus performing the correct binary coding operation. |
