To generate a dot pattern in which the ratio of black points per unit area in a binary image is increased as the density of a multi-value image is smaller in comparison with the dot pattern assigned with a basic threshold level data set in the assignment of the threshold level data with respect to a small cell when number of unit squares being components of the small cell is not in matching with the number of the threshold level data.
A dot pattern 3 has 9 unit squares, to which sets of basic threshold level data are assigned as 12, 24,..., 240. A dot pattern 41a is formed by rotating the basic pattern, the result is quantized to generate a small cell and threshold level data are assigned to unit squares being components of the small cell. For example, threshold level data = 12 denoting a minimum value are added to the set of the basic threshold level data and the set of the threshold level data obtained as a result of the addition is assigned to the dot pattern 41a. In the case that the small cell has 8 unit squares, the threshold level data = 12 denoting a minimum value are deleted from the set of the basic threshold level data and the set of the threshold level data obtained as the result of deletion is assigned to the small cell with the 8 unit squares.
ENDO HIROYUKI
TANABE JUNKO
KOIZUMI TAEKO
KONO MICHIKO
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