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.