Using a document scanner or other image input device of an image or document processing system to periodically scan or image printed test images from a plurality of marking engines replaces internal sensors as a feedback means in image quality control. For example, image lightness (L*) is controlled by periodically printing mid-tone test patches, scanning the printed test patches with a main job document scanner and analyzing the scanned image to determine updated marking engine actuator set points. For instance, ROS exposure and/or scorotron grid voltages are adjusted to maintain image lightness consistency between marking engines.