Abstract: The present application discloses methods and systems for calibrating a scanning system. The scanning system comprises a light-transmissive platen defining a top surface and a bottom surface, a controller, a document handler, and a scanner bar for recording image data from documents at various document heights. In one embodiment, the calibration method proposes the use of two calibration strips in a document scanning system that has both platen scanning and Constant Velocity Transport (CVT) scanning modes. In another embodiment, a scanner is disclosed with a dual calibration target or a single calibration target that is manufactured with two (2) different heights to correct the illumination profile at the CVT scanning height or at the platen scanning height.

Abstract: According to aspects of the embodiments, there is provided methods and systems for correcting illumination defects in document handlers. A document handler successively moves an image-bearing sheet past an image sensor, when the edges of the document passes over the edge guide near a constant velocity transport roll the document tends to flick down onto the image sensor causing a lightness change at the edges. The proposed correction is dynamically adjusting the light source or dynamically adjusting the automatic gain control (AGC) of the imaging sensor. The method comprises characterizing an optical signal reflected from an image-bearing sheet as it passes a scan window, determining the illumination defects in at least one edge region based on the reflected signal, and adjusting the gain of the imaging sensor or the light level during receipt of the optical signal.