| 摘要 |
PURPOSE:To correct a shading distortion of large variation with an A/D converter of bits small in number by D/A-converting a reference signal stored in a storage device then synchronizing it with each picture element of original- reading signal, and by inputting it to an A/D converter. CONSTITUTION:The reference signal is generated prior to the reading of the original, which is converted to a digital signal by an A/D converter 1 and is stored in a memory 2. The reference signal Vs stored in the memory 2 has a shading variation of DELTAV in the direction of a line l. When the reading of the original is started, the reference signal in the memory 2 is converted to an analog value by a D/A converter 3, and the resulting analog voltage is synchronized with the original-reading signal, and is supplied to the A/D converter 1 as a reference input Vref. In such way, the A/D converter 1 corrects the shading distortion of the original-reading signal VIN based on the reference signal Vref, and outputs it.
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