A shading correction method for an image reading apparatus configured to read an image formed on an original, while conveying the original, wherein the image reading apparatus comprises an image reading unit including an image sensor configured to read the image of an object on a reading position of said image sensor, a contact glass configured to guide the original to a first position, a reference member disposed at a location different from the first position, and a moving mechanism configured to cause relative reciprocating motion varying relative position of said reading position and said reference member, said image reading unit being fixed to a main body of the image reading apparatus, and a driving unit configured to drive the moving mechanism,
- the shading correction method comprising:
- a control step of controlling driving of the driving unit such that a reading position of the image sensor during a shading correction data acquisition period is set to a second position set on the reference member, and a reading position of the image sensor during an original image data reading period is set to said first position,
- wherein said control step comprises:
- a moving-time read data acquisition step of acquiring moving-time read data generated based on an output signal from said image sensor, while controlling said driving unit to drive said moving mechanism of said image reading unit from the outside of said image reading unit to move said image sensor;
- a detection step of detecting, based on the moving-time read data, that said reading position is at a boundary of a disposition area of the reference member;
- a driving amount acquisition step of acquiring a driving amount of the driving unit required during a time period from a start of said relative reciprocating motion to a time point when said detection means detects that said reading position is at said boundary;
- and
- a driving amount calculation step of calculating, based on the acquired driving amount, a first driving amount for use in varying the reading position of said image sensor to said first position, and a second driving amount for use in varying the reading position of said image sensor to said second position.