Patent ID: 8848246

Claim:
An image data generation method of generating halftone image data through halftone processing on a multi-tone color image, comprising: a) generating first halftone image data by performing halftone processing on a first color component image that is an image of a first color component of said color image, said first halftone image data indicating sizes of a plurality of dots of said first color component that are respectively to be formed at a plurality of pixel positions arranged in a matrix in a halftone image region; and b) after said operation a), generating second halftone image data by performing halftone processing on a second color component image with reference to said first halftone image data, said second color component image being an image of a second color component of said color image, and said second halftone image data indicating sizes of a plurality of dots of said second color component that are respectively to be formed at said plurality of pixel positions in said halftone image region, said operation b) including: b1) performing halftone processing on one pixel in said second color component image and provisionally determining a size of a dot of said second color component that is to be formed at a pixel position corresponding to said one pixel among said plurality of pixel positions; b2) obtaining a total dot size that is a sum of a first dot size and a provisional second dot size, said first dot size being a size of a dot of said first color component that is formed at said pixel position, and said provisional second dot size being the size of the dot of said second color component and being provisionally determined in said operation b1); b3) comparing said total dot size with a predetermined threshold dot size, and when said total dot size is less than or equal to said threshold dot size, determining a second dot size to be said provisional second dot size, said second dot size being the size of the dot of said second color component, and when said total dot size is greater than said threshold dot size, determining said second dot size to be a largest dot size within a range of a difference between said threshold dot size and said first dot size; b4) when said total dot size is greater than said threshold dot size in said operation b3), changing a pixel value of a group of neighboring pixels located at one or more pixel positions at which said second dot size has not yet been determined among pixel positions around said one pixel, on the basis of a pixel value of said one pixel and a difference between said provisional second dot size and said second dot size; and b5) changing said one pixel to a next pixel in accordance with a predetermined processing order of said plurality of pixel positions and repeating said operations b1) to b4).