Abstract: An image data generation device is provided with: an image data acquisition unit for acquiring image data; a division unit for spatially dividing the acquired data by a plurality of matrices; a priority order setting element for setting the priority order for performing gradation conversion of picture elements that make up the image data that corresponds to each of the matrices, and sets the priority order so that the priority order becomes lower going from picture elements located in the center of the matrix toward picture elements located on the outside edges of the matrix; a gradation conversion member for performing gradation conversion of the picture elements according to the priority order; and an image data generation unit for generating image data for printing based on a dot pattern that is formed by the picture elements after the gradation conversion.

Abstract: An image data generation device is provided with: an image data acquisition unit for acquiring image data; a division unit for spatially dividing the acquired data by a plurality of matrices; a priority order setting element for setting the priority order for performing gradation conversion of picture elements that make up the image data that corresponds to each of the matrices, and sets the priority order so that the priority order becomes lower going from picture elements located in the center of the matrix toward picture elements located on the outside edges of the matrix; a gradation conversion member for performing gradation conversion of the picture elements according to the priority order; and an image data generation unit for generating image data for printing based on a dot pattern that is formed by the picture elements after the gradation conversion.

Abstract: A control section 9 of a thermal printer 1 performs resolution conversion, gradation conversion, and CMYK color separation for input image data 3. After that, for image data of each color, the control section 9 performs shift processing for double-tone printing, to thereby obtain two types of image data. The control section 9 performs dot conversion and reverse shift processing for these image data, and prints the two types of image data in a superposed state. In the shift processing, the control section 9 shifts the image data of each color by the number of pixels corresponding to the resolution of the thermal printer 1 and the number of lines per inch. At that time, the image data of each color may be shifted by the corresponding number of pixels which differs among the colors. Further, for some colors, single-tone printing is performed, rather than double-tone printing, to thereby reduce the number of times of overprinting.