An image forming apparatus is disclosed for providing accurate shading corrections. The apparatus includes an illumination source for illuminating an image, and a photoelectric converter that receives reflected light from the image and photoelectrically converting the reflected light. The output signal from the photoelectric converter is amplified and converted to a digital signal. The digital signal is then subjected to shading correction. A controller is provided for ensuring that white reference data for a first sheet of copy is fetched from a stable region of the illumination source during shading correction. The white reference data is subsequently used when forming an image for a first sheet of copy.