| 摘要 |
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. Further, dot-on-dot processing, which is special shift processing, is performed for image data of a color to be printed second or later. Image data combining is performed such that the image data having undergone the dot-on-dot processing is used in a highlight region, and the image data having undergone the ordinary shift processing is used in the remaining region.
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