Image processing apparatus and storage medium that stores program associated with the apparatus

Abstract

A pseudo random number pattern which does not contain the minimum and maximum gradation values of pixels of input image data, and consists of, as elements, threshold values set at nearly equal intervals, is generated, and input image data is binarized by ordered dithering using this pseudo random number pattern. Since the elements of the pseudo random number pattern do not contain the minimum and maximum gradation values of the pixels of the input image data, even when a binary image is input, noise components, i.e., black or white isolated pixels can be prevented from periodically appearing. Since the threshold values of the pseudo random number pattern are set at nearly equal intervals, a dither image with quality as high as that can be obtained by the conventional method can be obtained even when a halftone image is input.

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