| 摘要 |
PURPOSE:To obtain a halftone image approximating an original halftone picture by using a large scanning aperture in a low space frequency area to express high gradation and using a small scanning aperture in a high space frequency area to reproduce an image having high resolving power. CONSTITUTION:In the case of a low space frequency area, namely, accordingly in the case of a picture like a gradation picture, a scanning aperture larger than the reference scanning aperture is selected. A condition formula deciding circuit 70 is used to determine which scanning aperture should be selected. In the case of a high space frequency area, namely, in the case of a picture like a line drawing or a character picture, the scanning aperture smaller than the reference scanning aperture is selected. A density pattern discriminating circuit 60 is used to determine which scanning aperture should be selected. Thus, a halftone image approximating the original picture is estimated even if the original halftone picture includes gradation pictures, line drawings and character pictures.
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