| 摘要 |
PURPOSE:To simplify production process and to achieve time shortening by providing an optical sensor, a density signal amplifying means, an amplification ratio control means and an exposure quantity control means and automatically setting an optimum amplification ratio by a CPU based on an input image density signal. CONSTITUTION:The optical sensor 4 receives light reflected by an original 1, and outputs the analog signal corresponding to light quantity. A gain selecting circuit 16 includes inverters 22 to 25, analog switches 18 to 21 and an operational amplifier 8, amplifies a signal output from the sensor and switches stepwise the amplification ratio. An offset adjusting circuit 17 includes operational amplifiers 9, 26 and 27, monitors the output level of a density signal means, sends a control signal according to the monitored result, and switches the amplification ratio. When the amplification ratio control means switches its amplification ratio, an original exposing quantity is controlled stepwise. These automatic adjustments are performed under the control of the CPU, and errors attending on the automatic switching of the amplification ratio are automatically corrected by an increase or decrease in the exposure quantity, thereby reading the same original with the same density. |
