Patent ID: 8130415

Claim:
An image forming apparatus which forms an image by using a printing head, comprising a plurality of printing elements, to scan a printing medium, comprising: an input unit adapted to input image data; a calculation unit adapted to calculate printing amounts for the respective printing elements for each main scan of the printing head in accordance with the image data; an N-ary unit adapted to generate a dot pattern to be formed by applying N-ary processing, with N being an integer not less than 2, to the printing amounts calculated by said calculation unit based on predetermined constraining condition information; and a generation unit adapted to generate the constraining condition information to be referred to by said N-ary unit for a next main scan based on the printing amounts calculated by said calculation unit and the dot pattern output from said N-ary unit, wherein said generation unit generates the constraining condition information so that a phase of the dot pattern to be generated by said N-ary unit has an opposite phase relationship in a part of a frequency region with respect to a dot pattern already printed on an identical region on the printing medium.