Patent ID: 7773776

Claim:
An image processing apparatus comprising: a halftone frequency determining section for determining a halftone frequency of an image that has been read from a document by an image reading apparatus, the halftone frequency determining section comprising: a flat halftone discriminating section for extracting information of density distribution from a segment block consisting of a plurality of pixels, and discriminating, based on the information of density distribution, whether the segment block is a flat halftone region in which density transition is low, or a non-flat halftone region in which the density transition is high; a threshold value determining section for determining a threshold value by using an adjusting value that is predetermined in accordance with a reading property of the image reading apparatus with respect to respective color components, the threshold value being for use in extraction of a feature of density transition between pixels; an extracting section for extracting, by using the threshold value determined by the threshold value determining section, the feature of density transition between pixels of the segment block which the flat halftone discriminating section discriminates as the flat halftone region; and a halftone frequency estimating section for estimating the halftone frequency, based only on the feature from the flat halftone region extracted by the extracting section.