| 摘要 |
PURPOSE:To prevent a checking pattern by providing plural dither matrices, obtaining the mean density level of the dot matrices of input image data, com paring the result with a specified threshold, and switching dither matrices using the threshold as a boundary. CONSTITUTION:A CPU 1 fetches the image data of (nXm) matrix from a mem ory 1, calculates the mean density in the data, and transmits the result to a selector 4. The selector 4 allows a pattern generation circuit 5 and a comparator 6 to execute a dither processing, in which the mean density and a density thresh old are compared with each other and the preliminarily provided dither matrices shown in the figures (a), (b) are selected. In the example shown by the drawing, the threshold is 50%, and the matrices in the figures (a), (b) are switched at <50% and >=50%. As a result, the checking pattern in an image that my occur at a time when the density is 50% can be eliminated.
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