| 摘要 |
PURPOSE:To obtain a binary coded circuit which is free of erroneous discrimination due to a decrease in the quantity of circumferential light, etc., and is stable without reference to aging, by providing a reference marker for threshold setting which has prescribed length and is colored with uniform density on the whole outside of an original readout region. CONSTITUTION:When a power switch is turned on, an operation command signal is sent out of a microcomputer 15 to a DC power source 16 and an image sensor 12 starts operation. Prior to an original readout, a reference reflective marker for threshold setting is read and its data is stored in the RAM of the microcomputer 15 through a sample holding circuit 18 and an A-D converter 19. Its digital value is used as a threshold level black-and-white discrimination during one scan of the image readout. As the image readout starts, a comparator 22 compares an image signal from an amplifier 20 with the threshold level stored in the RAM to obtain a binary coded signal close to original information under no influence of a decrease in the amount of circumferential light, etc. |
