Patent ID: 7215353

Claim:
An image forming apparatus, comprising: a photosensitive member configured to have a latent image written on a surface thereof; a modulation data storage device configured to store a plurality of different gray-scale pulse sets, each of said plurality of different gray-scale pulse sets including a plurality of gray-scale pulses having pulse widths differing from each other in steps of a predetermined value based on gray-scale information corresponding to gray-scale input image data values, wherein each of said plurality of gray-scale pulses are formed from a combination of at least two pulses including at least one left-positioned pulse and at least one right-positioned pulse; a pulse width modulator configured to select a gray-scale pulse set from among said plurality of different gray-scale pulse sets stored in said modulation data storage device in accordance with said gray-scale information contained in input image data, said pulse width modulator being configured to perform a pulse width modulation operation to control a light beam to turn on and off in accordance with said input image data at a rate corresponding to at least twice an image density of said input image data by using said gray-scale pulse set selected; and an optical writing mechanism configured to scan said light beam on said photosensitive member to form a latent image in accordance with said input image data; wherein said pulse width modulator is configured to control said light beam to turn on and off in units of pixel by synthesizing said left-positioned pulse varying in a predetermined pulse pattern and said right-positioned pulse varying in an other predetermined pulse pattern.