| 摘要 |
PURPOSE:To attain correct exposure by not only integrating the density of parts exceeding a certain density but also measuring the length of them and calculating an average density of a picture part to determine an exposure. CONSTITUTION:The quantity of reflected light of a preliminarily set density detection area on an original is detected by a light receiving sensor 11 and is subjected to prescribed amplification by an amplifying circuit 12 to obtain a detection voltage Va, and this voltage Va is inputted to an integrator 21 and a comparator 22, and the same reference voltage Vs is set to the integrator 21 and the comparator 22. The integrator 21 integrates the potential difference of only a part, whose detection voltage Va exceeds the reference voltage Vs, and outputs the integral value as VA, and the comparator 22 outputs ''1'' if the detection voltage Va exceeds the reference voltage Vs, and the comparator 22 outputs ''0'' otherwise, and the output value of the comparator 22 is supplied to an integrator 23. The integrator 23 integrates the input from the comparator 22 and outputs the integral value as VB, and a divider 24 divides VA by VB to output a control voltage Vd. The integral value VA corresponds to the overall quantity of densities of the picture part, and the integral value VB corresponds to the length of the picture part, and the voltage Vd corresponds to an average value of the density of the picture part. Thus, correct exposure is attained independently of the variance of the variable density of the original and the size of the picture part. |
