| 摘要 |
PROBLEM TO BE SOLVED: To fully utilize the hardware resolution of a printer in conformity with the printed image data to improve the apparent gradation properties and resolution and to attain the pseudo-smooth gray level of high resolution by preparing a plurality of dot matrix units (halftone dot sizes) which form halftone dots and selecting a dot matrix unit according to the image changing state of a pattern. SOLUTION: The (3×3) and (6×6) gray level transformation means 52 and 53 convert the dot data which are sample from a 256-multileveling data memory 50 by a (6×6) sampling means 51 into the (3×3) and (6×6) dot matrix data. A mean value calculation means 54 and 55 calculate the mean gray levels of dot matrixes. The (3×3) and (6×6) error component calculation means 56 and 57 calculate the screening errors from the lightness and mean gray levels of original image data received from the means 51. A halftone dot size selector 59 selects the halftone dot size of the smaller error of both screening errors according to the comparison result of a comparator 58.
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