Patent ID: 8339673

Claim:
An apparatus for processing an image, comprising; an inside and outside edge discrimination portion for discriminating whether a target pixel to be processed belongs to an inner side of an edge or an outer side of the edge; a threshold function storing portion for storing a plurality of variable threshold functions corresponding to input image data and a threshold value; a threshold value generating portion for generating a plurality of threshold values, each of the threshold values being determined by input image data and a respective one of the variable threshold functions; a threshold value selecting portion for selecting one of the plurality of threshold values for an error diffusion process in accordance with a discrimination result discriminated by the inside and outside edge discrimination portion and outputting the selected threshold value; and an error diffusion process portion for performing the error diffusion process for multilevel input data concerning the target pixel by utilizing the threshold value generated by the threshold value generating portion so as to produce output data whose gradation steps are reduced.