| 摘要 |
In order to reproduce a gradation image of a plurality of colors with dither method, a plurality of patterns including first and second patterns are provided which makes dot in the reproduced image grow as lines and as lumps as gradation level increases with increase in gradation level. One of the patterns for a color of the received image data is selected, and received multi-level image data are screened with the selected pattern to generate bi-level image data for reproducing the image. In a different way, a plurality of patterns including first and second patterns are provided which make dots to be reproduced grow discretely along lines at low gradation levels as the gradation level increases. Screen angles of the first and second patterns are different by 90° from each other. One of the patterns is selected based on a color of received image data, and the received image data are screened with the selected patterns to generate bi-level image data. Thus, color shift or color nonuniformity in the reproduced image is suppressed, and image quality of full-color or multi-color reproduction image is improved.
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