1. An image processing apparatus for generating binary or multiple-value image data for forming an image on a recording medium by ejecting droplets from nozzles of nozzle rows of a recording head while relative movement between the recording medium and the recording head is caused, the nozzles serving as ejection ports for ejecting the droplets, the image processing apparatus comprising a multiple value conversion device which carries out quantization processing of original image data having multiple tones (M values) so as to convert the original image data to image data of N values having fewer tones than the original image data (where M and N are integers satisfying M>N≧2), wherein: the recording head has a two-dimensional nozzle arrangement in which the nozzle rows are arranged in a first direction which is a direction of the relative movement between the recording head and the recording medium, and the multiple value conversion device generates the image data of N values representing a dot pattern having blue noise characteristics in the first direction and green noise characteristics in a second direction which is a direction perpendicular to the first direction on the recording medium so as to achieve tonal representation based on the dot pattern having these frequency characteristics.