Shading correction data used in an image reading apparatus for
shading-correcting image data obtained by reading an original image by a
line sensor is acquired. A defect position on a white reference plate and
a defect correction coefficient for correcting shading correction data at
this defect position are obtained, and the shading correction data at the
defect position is corrected by using the defect correction coefficient.
Shading correction is performed by using the corrected shading correction
data.
