Patent ID: 7170643

Claim:
An image reading apparatus, comprising: a light source adapted to illuminate an original sheet; an image sensor adapted to scan said original sheet and output electrical signals; a feeder capable of successively supplying a plurality of original sheets to an original sheet scanning area of said image sensor; a first reference member which is arranged in the original scanning area of said image sensor in a sub-scanning direction; a second reference member which is arranged in an area other than the original sheet scanning area of said image sensor in the sub-scanning direction; a memory adapted to store a predetermined time since said light source is turned on until a maximum of electrical signals output from said image sensor at the time said light source is turned on changes a predetermined rate; a timer adapted to measure an on time since said light source is turned on; and a controller adapted to determine whether the time measured by said timer reaches the predetermined time, in a case that the predetermined time has not elapsed, control said image sensor to scan said first reference member illuminated by said light source for acquiring a coefficient for uniformly changing level of the electrical signals while said image sensor scans the plurality of original sheets which are successively supplied by said feeder, and in a case that the predetermined time has elapsed, control said image sensor to interrupt the scanning operation of the plurality of original sheets and scan said second reference member illuminated by said light source only once for acquiring shading correction data in a main scanning direction, and then restart scanning of the remaining original sheets and scan said first reference member illuminated by said light source while said image sensor scans the remaining original sheets without scanning said second reference member.