Method of setting reference data of shading corrections, and image reading apparatus

An image reading apparatus comprising:

• an image sensor which includes a plurality of photosensor elements;
• an optical system which includes a light source for illuminating a subject, and which inputs an optical image to the image sensor;
• a processing unit which outputs image data expressive of the optical image on the basis of output signals of the image sensor,
• a white reference image input unit for inputting a white reference image to the image sensor with the light source lit up;
• a white reference setting unit for setting white reference data every effective photosensor element by inspecting the output signals of the image sensor as to the white reference image;
• a black reference image input unit for inputting a black reference image to the image sensor with the light source extinguished after the white reference image has been inputted;
• a black reference setting unit for setting black reference data every effective photosensor element by inspecting the output signals of the image sensor as to the black reference image;
• and
• a reading unit for inputting the optical image of the subject to the image sensor with the light source lit up, and causing the processing unit to output the image data outputted to shading corrections with the white reference data and the black reference data.