Patent ID: 8396384

Claim:
A sheet type determination apparatus comprising: a tray configured to hold a sheet bundle formed by sheets which are stacked, the sheet bundle comprising an upper surface, a lower surface and a plurality of side surfaces extending in a stacking direction; a light source configured to emit illumination light to a first region on at least one first surface selected from the side surfaces; a first detection unit configured to detect a first light intensity distribution of first transmitted light emerging from a second region on at least one second surface selected from the upper surface and the lower surface, the first transmitted light being generated as the illumination light which passes through the sheet bundle, and the second region being different from the first region; a database configured to store a table describing a relation between reference attenuation rates and sheet types; and a sheet type determination unit configured to calculate an attenuation rate of the first transmitted light based on the first light intensity distribution, and determine a type of the sheets by comparing the attenuation rate with the reference attenuation rates.