An image processing apparatus, method, and computer program product including a carriage for carrying an image reading device; a white plate arranged above a track of the carriage, and read by the image reading device for adjusting a reading level; a home position sensor to detect the position of the carriage; and a controller to control the movement of the carriage. The controller is configured to determine the direction of movement of the carriage based on the output of the home position sensor, and to perform a tentative homing operating when the home position sensor changes its output after the carriage is moved.