Image forming apparatus configured to perform exposure control and exposure method

摘要

The data conversion unit of an image forming apparatus converts input image data into dot image data in which pixel values having gradation information are arranged in a matrix. A storage unit stores optical face tangle error information of each reflecting surface of a rotary polyhedron. An assignment unit assigns a number to each of the plurality of reflecting surfaces, specifies by which of the plurality of reflecting surfaces light emitted for each line of the dot image data is to be reflected and assigns the number of the reflecting surface to each line of the dot image data. A determination unit determines a light emission mode corresponding to the dot image data based on the optical face tangle error information and the number of the reflecting surface. An exposure control unit causes the light source to emit light in accordance with the determined emission mode.

主权项

1. An image forming apparatus, comprising:
an image bearing member on the circumferential surface of which an electrostatic latent image is to be formed; a data conversion unit for converting input image data into dot image data in which pixel values having gradation information are arranged in a matrix; a light source for emitting light modulated according to the pixel values for each line of the dot image data to form the electrostatic latent image on the circumferential surface of the image bearing member; a deflecting mechanism including a rotary polyhedron having a plurality of reflecting surfaces for reflecting light emitted from the light source and a driving member for driving and rotating the rotary polyhedron and adapted to scan the light emitted from the light source in a main scanning direction on the circumferential surface of the image bearing member by driving and rotating the rotary polyhedron by the driving member; a storage unit for storing optical face tangle error information of each reflecting surface of the rotary polyhedron; an assignment unit for assigning a number to each of the plurality of reflecting surfaces, specifying by which of the plurality of reflecting surfaces light emitted for each line of the dot image data is to be reflected and assigning the number of the reflecting surface to each line of the dot image data; a determination unit for determining to the writing timing of each of the dot image data based on the optical face tangle error information, the number of the reflecting surface and the pixel values of the dot image data; and an exposure control unit for causing the light source to emit light in accordance with the determined writing timing, wherein the determination unit: specifies, out of the respective reflecting surfaces, one reflecting surface and the reflecting surface one before the one reflecting surface, an interval in a sub scanning direction between spots of light reflected by which on the circumferential surface of the image bearing member is wider or narrower than a predetermined reference pitch from the optical face tangle error information; and determines the writing timing of the line of the dot image data to which the number of the specified reflecting surface is assigned based on the pixel values of this line and the pixel values on the line one above this line, successively sets a target pixel for non-white pixels for one line of the dot image data to which the number of the specified reflecting surface is assigned; increments a first count number when a pitch between the one line and the line one above the one line is wider than the reference pitch and increments a second count number when this pitch is narrower than the reference pitch if a pixel right above and a pixel at the upper right side are white and a pixel at the upper left side is non-white when viewed from the target pixel in data indicated by the line one above the one line; increments the second count number when the pitch between the one line and the line one above the one line is wider than the reference pitch and increments the first count number when this pitch is narrower than the reference pitch if the pixel right above and the pixel at the upper left side are white and the pixel at the upper right side is non-white when viewed from the target pixel; and determines to relatively advance the writing timing of the one line with respect to the line one above by a predetermined time when the first count number is larger than the second count number and to relatively delay the writing timing of the one line with respect to the line one above by a predetermined time when the second count number is larger than the first count number.