Image reading apparatus and sheet processing apparatus

A sheet processing apparatus comprising:

• a conveyance device which convey a sheet;
• a first illumination device which irradiate light at a first angle onto the sheet that is being conveyed by the conveyance device;
• a second illumination device which irradiate light at a second angle onto the sheet that is being conveyed by the conveyance device;
• an illumination controller which switch between a first irradiation state in which light is irradiated from the first illumination device and the second illumination device onto the sheet and a second irradiation state in which light is irradiated from either the first illumination device or the second illumination device onto the sheet;
• an imaging device which acquire a first comparable image in the first irradiation state, and to acquire a second comparable image in the second irradiation state;
• a defect detector which detect a defect of the sheet based on a difference between the first comparable image and the second comparable image;
• an identification device which identify the sheet based on a result of detection by the defect detector;
• and
• a classification processor which classify the sheet based on a result of identification by the identification device.