Patent ID: 7834897

Claim:
A method for controlling an optical scanning apparatus comprising: generating an exposing signal from a pattern data for an optical scanning apparatus, which includes a light source that emits a light beam, a deflector that deflects the light beam emitted from the light source by means of a deflection mirror surface oscillating sinusoidally, and a scanning optical system that has an arcsine characteristics and that images the light beam deflected by the deflector on a surface-to-be-scanned in a spot, and which makes the imaged spot scan the surface-to-be-scanned in the main scanning direction while modulating the light beam emitted from the light source based upon the pattern data indicating a position on the surface-to-be-scanned the light beam exposes so that the light beam exposes a predetermined position on the surface-to-be-scanned, the exposing signal being a train of pulses arranged on a time axis in accordance with an arrangement in the main scanning direction of values, which the pattern data have, indicating exposure or non-exposure of the light beam, a pulse width of each pulse of the pulses being width of time corresponding to a length, indicated by the pattern data, in the main scanning direction of an exposing area of the light beam; correcting the exposing signal to generate a corrected exposing signal by varying pulse width of each pulse of the pulses which compose the exposing signal in accordance with a distance between the exposing area corresponding to the pulse and an optical axis of the scanning optical system; emitting the light beam from the light source modulated by the corrected exposing signal; and executing a halftone processing in which arranging hypothetically a plurality of cells composed of plural pixels adjoining each other on the surface-to-be-scanned, and comparing an image tone data, which indicate position and a tone level of each of the plural pixels, with a dither matrix for each cell, thereby generating the pattern data that indicate a position in the cell for the light beam to expose in a spot-like fashion, wherein the pulse width of each pulse/both of the pulse width of each pulse and light quantity of the light beam is/are varied in accordance with a distance between the exposing area and an optical axis of the scanning optical system, and in correcting the exposing signal to generate the corrected exposing signal, pulse width of each pulse of the pulses which compose the exposing signal is converted based upon a conversion pattern that increases the pulse width in accordance with a distance in the main scanning direction between the exposing area corresponding to the pulse and the optical axis of the scanning optical system.