| 摘要 |
PROBLEM TO BE SOLVED: To improve gradations at the low density image input time without reducing the number of total gray levels in a dither matrix by providing a storage means for storing the threshold level of a low gray level in the matrix as a specified type. SOLUTION: A threshold memory 3 for storing the threshold level defined by the dither matrix stores the threshold level of the low gray level in the matrix as a type M (0<=M<m). In the case of three threshold levels corresponding to an address to take the lowest gray level among 3×3, for example, the totally overlapped equal value is stored in advance. The input image is compared with an (m) threshold level image in the matrix of m×n (n>=3) and based on binary data generated corresponding to the compared result, the input image is processed while referring to and comparing with the threshold memory 3 and by decreasing the number of gray levels in the image pixel of the low gray level from (m) to M, the pixel can be prevented from being isolated with the low density so that the gradations can be improved without reducing the number of total gray levels. |
