Image forming apparatus having an exposure device changing pulse width of a light beam based on pattern data of an image

Abstract

An image forming apparatus using a multi-scan system is capable of forming an image at a high speed. An exposure device scans a surface of the photo conductor by light beams emitted by a plurality of light-emitting elements so as to simultaneously form a plurality of electrostatic latent images at a plurality of positions on the photo conductor, a pitch of the light beams in a sub scanning direction being smaller than a beam diameter defined by a value of an intensity of the light beam at which an intensity level of each light beam is 1/eof an intensity level at a center thereof, the electrostatic latent image being formed also at a position where the plurality of light beams overlaps with each other. A code of a plurality of levels is produced from image data in accordance with a pattern detection matrix. A pulse with output from the pattern detection processing means is produced with reference to pulse width data which designates a pulse width of each light beam previously set in response to the code.