Patent ID: 7688342

Claim:
An image forming apparatus, comprising: an image carrier member; a light source having a plurality of light-emitting portions, each of which emits a light beam based on input image data; a rotating polygonal mirror having a plurality of mirror planes each of which deflects and scans the light beams emitted from said light source to form a plurality of scanning lines on said image carrier member, wherein each of the mirror planes has an associated amount of plane tilt that causes the light beam to be offset from the desired location on the image carrier member by the amount of plane tilt; a control unit which selects, for each of the mirror planes, a corresponding light-emitting portion based on the amount of plane tilt, whereby the offset of the spot of the light beam from the light source on the image carrier member caused by the plane tilt of the mirror plane is reduced by the offset associated with the spot generated by the selected corresponding light-emitting portion; and a driving unit which drives said light source according to image data so as to emit the light beam only from the light-emitting portion selected for each of the mirror planes.