Abstract: An image reading apparatus that includes an image scanning module in which an image sensor device is provided. The image reading apparatus includes an upper housing and a pattern located on the bottom surface of the upper housing and positioned at a position x with reference to the edge of the opening. The upper housing has a bottom surface and is provided with an opening for mounting a transparent platen adapted for supporting a document to be scanned. The opening defines an edge. Responsive to detection of the pattern by the image sensor device, the image reading apparatus determines the distance required to move by the scanning module to reach a predetermined positioning line.

Abstract: A method for positioning the initialization position of a light source for an image reading apparatus operated under a passing-light mode is provided. A platen including a reference area that provides a pattern disposed at a position x is provided. The method comprises a first step of positioning the scan model at the position x in order to read the pattern within the reference area. Secondly, the method moves the light source toward the reference area and, at the same time, triggers the scan module to scan the image. Thirdly, repeat the second step until the image scanned by the scan module meets a pre-determined criterion. Fourthly, the method makes the light source module further move a distance of .DELTA.D-.DELTA.d. The .DELTA.d is the distance traveled by the light source during an interval which begins at the capture of the pattern by the scan module and ends at the determination of the pre-determined criterion as being met.