| 摘要 |
PURPOSE:To accomplish a proper picture quality in accordance with an original picture by obtaining the frequency distribution of picture element value level over k (provided k=mXn) pieces of level areas when converting the respective picture element value of an original picture to a binary signal as comparing the said value with a threshold matrix of mM lines X nN rows, and by determining the elements of the respective mztrix of k-pieces of layers corresponding to the said distribution. CONSTITUTION:When converting the respective picture element value of an original picture to a binary signal by comparing the said value with the threshold matrix of mM lines XnN rows, the frequency distribution of the picture element value level is obtained over k (provided k=mXn)-pieces of level areas. In the mean time, the threshold matrix is decomposed into multi-layer matrices of K-layers made up of MXN elements, to determine the elements of the said multi-layer matrices in accordance with the obtained frequency distribution above mentioned. In case providing 64-grade-gradation by an 8X8 matrix, the matrix is decomposed into four layers of 4X4 dither matrices. And, the picture element value level of the target original picture is divided into four divisions (l=1-4). The number of picture elements whose values are in respective one of the said divisions is counted. The divisions of =4 and =1 are allocated to a resolution-respected-type dither method while ones of =3 and =2 are to the gradation-respected-type. In such way, a dither matrix of 8X8 is constituted.
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