| 摘要 |
PURPOSE:To correct shading distorting with a small-sized memory by differentiating a digital-convertion value of an input signal to store the result in a memory, and D/A-converting the output from the said memory to supply it to an A/D converter as a reference signal. CONSTITUTION:First, a reference plane entirely white is read by a line sensor 21, to obtain a reference read-signal that includes the width of shading variation. The said signal is converted to a digital signal by an A/D converter 11, and further digital-differentiated by a digital differentiator circuit 12 in order that a large output is generated for an input of large variation and a small one for that of small variation. The said output generated is stored in a memory 13. Then, when the reading of an original is started, an original-reading signal VIN is inputted by a line sensor 21 to the A/D converter 11. In synchronization with it, the data that shows the proportion of variation of shading is read out from the memory 13, D/A-converted, and supplied to the A/D converter 11 as the reference signal.
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