| 摘要 |
PROBLEM TO BE SOLVED: To provide a document reader which can implement the precise base color removal by deducing a lower reference voltage value from a peak hold value and then multiplying the obtained value by a gain. SOLUTION: As shown in Fig. 2, Vdark (black offset value) and VRB (lower reference voltage of A/D converter) are inputted to an AMP part. Fig. 3 shows a circuit diagram (inside of the AMP part), and the corresponding formula of the circuit is shown below the figure, in which the value obtained by deducting the lower reference voltage value from the peak hold value, is multiplied by R1/R2, then the lower reference value is added. The result is to be inputted to the upper reference voltage. Fig. 5 shows a circuit in which Vdark is also deducted, with the corresponding formula below. That is, this circuit is the combination of the circuit in Fig. 3 with a circuit for deducing Vdark, where Vdark does not need to be added after the gain multiplication.
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