Patent ID: 8482789

Claim:
An image reading apparatus comprising: a feeder which transports a document; a first reading unit which reads a surface of the document transported in a transporting direction by the feeder, the first reading unit being configured to read the surface of the document in a main scan direction at a first reading position; a first memory which stores image data of the surface of the document read by the first reading unit; a second reading unit which reads one surface of the document in the main scan direction at a second reading position located at an upstream side of the first reading position with respect to the transporting direction by a predetermined distance; a second memory which stores image data of the document read by the second reading unit; and a controller configured to control the feeder, the first reading unit and the second reading unit to execute: pre-scanning the document by the second reading unit over a predetermined range shorter than a separation distance between the first reading position and the second reading position in a transporting direction from a leading edge of the document when the document transported by the feeder reaches the second reading position; storing obtained pre-scanned image data into the second memory; measuring the size of the document based on the pre-scanned image data stored in the second memory; reading the surface of the document by the first reading unit with a predetermined reading resolution when the document transported by the feeder reaches the first reading position; setting a transporting speed of the document based on a transporting speed table, such that a time for transporting the document from the end of the predetermined range to the first reading position is greater than a processing time for measuring the size of the document; storing obtained first image data into the first memory; and processing the first image data stored in the first memory based on the size of the document obtained in the measuring.