| 摘要 |
PURPOSE:To correct shading without using a computing element, etc., by setting a reference value against the analog output of a white-reference picture output data in accordance with the light-quantity variation, and by comparing the analog output with video data. CONSTITUTION:Prior to starting the reading of an original, the one-line-reading output obtained by reading a reference white plane 23 is stored in a ROM 3 each bits. Then the original is read by a sensor unit 1, and the resulting signal is supplied to a comparator 6 via an amplifier 2. Meanwhile, the white- reference value stored in the ROM 3 is read out every 1-bit, and is converted to an analog signal by a D/A converter 4. At this time, the illuminance of the LED array included in the sensor unit 1 is monitored by a light-quantity detector 7, and its level is set by a variable resistor 8, and then is supplied to the converter 4 as a reference voltage Vref 1. Accordingly, the output of an amplifier 5 also varies in accordance with the light-quantity variation. In result, a stabile binary signal is obtained from the comparator 6.
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