| 摘要 |
PROBLEM TO BE SOLVED: To detect a defect such as dust on a shading correction plate so as to eliminate the effect thereby. SOLUTION: A line sensor respectively reads the shading correction plate at plural displacement positions other than a home position on the shading correction plate (S1, S5), and shading correction data are calculated at each displacement position and for each photoelectric conversion element on the basis of read data (S2, S6). A mean value of the calculated shading correction data of each photoelectric conversion element over the displacement positions is calculated on the basis of the calculated shading correction data to obtain mean shading correction data (S9). The line sensor reads the calculated shading correction data at the home position on the shading correction plate, shading is corrected by the means shading correction data on the basis of the obtained read data (S12 in Figure 10), and at least a defect position of the shading correction plate is specified on the basis of the data after the correction (S17).
|
