JP2898321B

PURPOSE:To reduce an estimate error while taking the correlation with peripheral picture elements into account by obtaining mean density based on a picture element data corresponding to the size of a dither matrix, deciding the range of estimate of an intermediate tone of a noted picture element and estimating the intermediate tone based on the state of picture elements in the vicinity thereof. CONSTITUTION:A picture element data of an input picture element corresponding to the size of a dither matrix is fetched by a picture element input means 111 and the average density of the noted picture element is obtained by an average density calculation means 121 based on number of black level picture elements included in the input picture elements. An estimate range decision means 131 decides the estimate rage of the intermediate tone in response to the estimate error based on the average density corresponding to the noted picture element, a threshold level in the relevant dither matrix and the picture element data of the noted picture element. Moreover, an intermediate tone estimate means 141 applies intermediate tone estimate in response to the state of the picture element placed in the vicinity. Thus, the estimate error is reduced by taking the correlation with the surrounding picture elements into account.