Dust and dirt detection in image reading apparatus having original flow scanning function

A dust detection method in an image reading apparatus having a document feeder adapted to convey an original, and an image sensor adapted to read the original conveyed to a platen by the document feeder, comprising:

• controlling the 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 the document feeder;
• adding for each pixel image data of the original convey member read the plurality of number of times;
• storing for each pixel the added image data in a memory;
• determining a threshold value on the basis of the number of times of reading the original convey member and the image data stored in the memory;
• and detecting 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 the image sensor without placing any original on the platen.

A computer program product comprising a computer readable medium having computer readable program code embodied in said medium for a dust detection method in an image reading apparatus having a document feeder adapted to convey an original, and an image sensor adapted to read the original conveyed to a platen by the document feeder, said product including:

• first computer readable program code for controlling the 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 the document feeder;
• second computer readable program code for adding for each pixel image data of the original convey member read the plurality of number of times;
• third computer readable program code for storing for each pixel the added image data in a memory;
• fourth computer readable program code for determining a threshold value on the basis of the number of times of reading the original convey member and the image data stored in the memory;
• and fifth computer readable program code for detecting 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 the image sensor without placing any original on the platen.