Patent ID: 7701614

Claim:
An image processing method for performing halftoning of a digital image constituted by an array of pixels having grayscale values which correspond to a content of the digital image, the method comprising the steps of: grouping the pixels constituting the digital image into a first group and a second group in accordance with a predetermined distribution pattern without regard to the grayscale values of the pixels, the first group comprising pixels located in first preselected pixel positions, the pixels of the first group being preselected to undergo subsequent diffusion of a quantization error generated through quantization to a peripheral pixel, the second group comprising pixels located in second preselected pixel positions, the pixels of the second group being quantization to a peripheral pixel; performing a first quantization process on the pixels belonging to the first group using a threshold matrix composed of a plurality of threshold values; determining the quantization error generated during the first quantization process; diffusing the quantization error obtained in the quantization error determining step to at least one non-quantized pixel belonging to the second group which is adjacent to the pixel subjected to the first quantization process; performing a second quantization process, using a threshold matrix, composed of a plurality of threshold values, on the non-quantized pixel to which an error value is diffused during the quantization error diffusing step; and outputting a visible image through an image forming apparatus according to halftone image data obtained through the first quantization process and the second quantization process; wherein the pixels of the first group are distributed at substantially uniform and regular intervals separated by the pixels of the second group.