| 摘要 |
PURPOSE:To satisfactorily estimate an original halftone picture from a multivalued picture (multivalued dither picture, for instance) by selecting an aperture satisfying the prescribed conditions among plural types of apertures by moving in units of picture elements and estimating a picture based on the mean value of multivalued levels in the aperture. CONSTITUTION:Plural types of apertures are set in the multivalued picture composed of multivalued levels. Among them the aperture satisfying the prescribed conditions is selected by moving at every picture element, and the halftone picture is estimated according to the mean value of the multivalued levels in the aperture. Namely, in accordance with a threshold matrix the original halftone picture is converted into a white, grey and black ternary picture (multivalued dither picture), and conditions that there is no change in a picture element level are decided as inequalities show. Where the central positions of the apertures of the multivalued dither picture are 2 and 2, a=7, b=12, c=13 and d=24 hold, and the optimum aperture is C. Since the sum of the multivalued picture element levels at an initial position is c=12 and the gain of the opening C is 2, the halftone picture estimated value comes to 13X2=26.
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