Patent ID: 8587836

Claim:
An image forming apparatus which forms a visible image by exposure scanning and development on an image carrier and transfers the visible image to a print medium, the apparatus comprising: an averaging unit configured to average H pixels, where H is not smaller than 2, adjacent in a subscanning direction serving as a conveyance direction of the print medium in an input image, thereby reducing a size to 1/H in the subscanning direction; a multi-level error diffusion unit configured to perform multi-level error diffusion processing for each pixel in an output image from the averaging unit; a H-pixel reconstruction unit configured to replace each pixel in an output image from the multi-level error diffusion unit with H pixels adjacent in the subscanning direction; and a generator configured to generate an exposure control signal for performing the exposure scanning, based on an output image from the H-pixel reconstruction unit, wherein the H-pixel reconstruction unit has a selection table including M×N elements, where M and N each are integers, with one of M or N being at least 1 and the other of M or N being at least 2, wherein each element included in the selection table has information specifying one of a plurality of reconstruction tables each representing a combination of H pixels, in the subscanning direction, including a pixel having a higher density and a pixel having a lower density, and the elements are arranged to give a screen angle, and wherein the H-pixel reconstruction unit generates the screen angle by selecting, from the selection table, one reconstruction table, among the plurality of reconstruction tables, representing a combination of the densities of the H pixels in accordance with a position of the pixel in the output image from the multi-level error diffusion unit.