Patent ID: 8320021

Claim:
An image processing apparatus which quantizes a pixel value of each of a plurality of pixels contained in an input image, based on a quantization threshold, performs an error diffusion process of diffusing a quantization error generated by quantization to a neighborhood pixel of each pixel, and generates an output image of halftone, comprising: a storage section for storing a plurality of sets of diffusion coefficients for the error diffusion process; a halftone frequency obtaining section for obtaining a halftone frequency based on a pixel value of an input image; a zoom process section for zooming the input image with a required zoom level; and a process section for selecting an individual set of diffusion coefficients for each pixel or the same set of diffusion coefficients for each pixel from the sets of diffusion coefficients stored in said storage section, based on a combination of the halftone frequency obtained by said halftone frequency obtaining section and the zoom level with which the input image is zoomed by said zoom process section, and performing the error diffusion process based on the selected set of diffusion coefficients and the quantization error.