| 摘要 |
PROBLEM TO BE SOLVED: To improve deterioration in quality of converted data encountered at the end of image data in error diffusion processing. SOLUTION: When a pixel of image data represented by multi-valued gradation values is binarized or converted to a predetermined plurality of values, an error between a converted value of the target pixel to be converted to a plurality of values and an original value is found, and the error is distributed to other unprocessed pixel. At an end of a scan line of the image data, expanded pixel areas (12) (14) with one to several pixels of virtual pixels included therein are provided. The density of the virtual pixels within the expanded pixel areas (12) (14) is set to a predetermined value, and the error is distributed to or from the virtual pixel within the expanded pixel areas (12) (14). The expanded pixel areas (12) (14) are provided at both ends of the scan line of the image data. The density value of the pixels within the expanded pixel areas (12) (14) is set to be the same as that of a pixel at the end on the scan line of image data adjacent to the virtual pixel.
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