1. An image processing apparatus comprising: a multi-level unit configured to apply 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 configured to acquire a number of screen lines of the binary halftone dot image data; a tone correcting unit configured to determine a tone correction amount corresponding to the number of screen lines of the binary halftone dot image data acquired by the acquiring unit, and configured to apply 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 configured to binarize 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, wherein the apparatus further includes a setting unit configured to set the number of screen lines of the binary halftone dot image, and wherein the acquiring unit is configured to acquire the number of screen lines which is set by the setting unit.