| 摘要 |
PROBLEM TO BE SOLVED: To provide a proper digital density value with respect to dot images which form intermediate density. SOLUTION: An A/D converting part 102 converts an analog signal outputted by a line sensor 101 to a digital signal, on the basis of a reference voltage. A data processing part 103 performs shading correction. A data processing part 104 performs gamma-correction processing and binarizing processing. On the basis of digital signals for one line shading-corrected by the data processing part 103, a counter 105 counts the number of pixels, which have an image signal level higher than the reference voltage of the A/D converting part 102. When the counted number of pixels is more than a prescribed upper limit value or less than a prescribed lower limit value, a discrimination part 106 changes the reference voltage of the A/D converting part 102.
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