| 摘要 |
PURPOSE:To detect accurately a density of an original picture without providing a large number of detecting means in the direction intersecting the scanning direction. CONSTITUTION:Detected optical information of the density condition of an original picture by means of photodetector element 21 is impressed upon a holding circuit 104 after it is converted into electric signals at a detecting circuit. The circuit 104a of the circuit 104 selectively holds the densest signal and the circuit 104b selectively holds the lightest signal. Output of the circuits 104a and 104b are impressed upon a differential amplifier 105 and a control output corresponding to the output difference is led out. The control output is impressed upon a circuit 101 controlling the intensity of illumination of a lighting lamp 4 as an illumination intensity controlling signal through a gate 106. A reference power source 107 which applies a control voltage, under which the lamp 4 exerts prefixed reference intensity of illumination, across the circuit 101 is connected with the other input of the gate 106. |
