Patent ID: 7119926

Claim:
An image reading apparatus comprising: a document feeder adapted to convey an original; an image sensor adapted to read the original conveyed to a platen by said document feeder; a controller adapted to control said image sensor to execute reading at a predetermined position a plurality of number of times without placing any original on the platen while driving an original convey member of said document feeder; an adder adapted to add for each pixel image data of the original convey member read the plurality of number of times; a memory adapted to store for each pixel the image data added by said adder; a determination unit adapted to determine a threshold value on the basis of the number of times of reading the original convey member and the image data stored in said memory; and a detector adapted to detect a presence/absence and position of dust and/or dirt on the platen on the basis of the threshold value and image data output from said image sensor without placing any original on the platen.