1. An image processing apparatus comprising: a multi-level unit that applies a multi-level process on binary halftone dot image data indicating a binary halftone dot image, to form multi-level image data; an acquiring unit that acquires a number of screen lines of the binary halftone dot image data; a tone correcting unit that determines a tone correction amount corresponding to the number of screen lines of the binary halftone dot image data acquired by the acquiring unit, and that applies tone correction on the multi-level image data produced by the multi-level unit, by using the determined tone correction amount; and a re-binarizing unit that binarizes the multi-level image data in which the tone is corrected by the tone correcting unit, without changing a halftone dot shape of the binary halftone dot image data, to produce re-binarized halftone dot image data.