The invention provides an image processing device, comprising: an N-level quantization unit, where N is a natural number equal to or greater than 2, the unit converting multi-level image data into N-level image data, the multi-level image data including a plurality of pixels, each pixel having a value corresponding to one of a multi-level gradation, and the N-level image data including a size of an ideal ink dot to be formed; a memory that stores error information, the error information corresponding to a difference between an ideal ink dot and an actual ink dot, the actual ink dot being formed by an image forming device, the image forming device having a plurality of nozzles, and each of the plurality of nozzles being associated with an ideal ink dot and an actual ink dot, and being capable of ejecting M-number of ink dot sizes, where M is a natural number equal to or greater than 2 and satisfies M≧N); an error information obtaining unit that obtains from the memory error information corresponding to an identified one of the plurality of nozzles, the identified nozzle being used for image processing; a dot size determining unit that determines a size of an ink dot on the basis of the error information, the ink dot being ejected by the identified nozzle, and a size of the ink dot being determined such that a density of the ejected ink dot is approximately equal to a required density, the required density being determined by the N-level image data; and an output unit that outputs to the image forming device an instruction for causing ejection of an ink dot from the identified nozzle, the size of the ejected ink dot being determined by the dot size determining unit.