Image reading apparatus and image forming apparatus equipped therewith

An image forming apparatus comprising a document reading apparatus, which comprises:

• an optical system including an exposure unit which is operable as at least one of:
• (i) a stationary document reading system which scans and exposes a stationary document placed on a platen while the exposure unit moves so as to read an image of the stationary document, and (ii) a moving document reading system which scans and exposes a moving document while the exposure unit is stationary so as to read an image of the moving document;
• and
• a reference density plate for shading correction which is provided so as to extend along a main scanning direction on a platen glass for the moving document reading system so as to face the exposure unit of the optical system;
• wherein the optical system scans, along the main scanning direction, both a first collection position and a second collection position on the reference density plate, which are at different positions on the reference density plate along a sub-scanning direction that is perpendicular to the main scanning direction, so as to obtain first shading correction data and second shading correction data, respectively, for performing the shading correction;
• and
• wherein one of the first collection position and the second collection position is corrected to a new position along the sub-scanning direction, based on the obtained first and second shading correction data.