| 摘要 |
PURPOSE:To simplify a program or a circuit constitution and to shorten by setting a prescribed functional relation between a reference original density value and a dot area ratio according to the density characteristic of a successive gradation picture and rewriting a threshold every time of the setting. CONSTITUTION:A dot generator 2 has a comparator 9, a density corresponding value from an original reading part 1 and the threshold from a threshold output part 4 are inputted and the density corresponding value is binarized by the threshold. The CPU 12 of the threshold output part 4 reads the dot area ratio PX to the prescribed number of generating the dots from the storage table 14 of the number N of generating the dots - the dot area ratio P. Then, the reference original density value DX to the dot area ratio PX is read from the storage table 15 of the P - reference original density value D. Further, a reading density corresponding value VX to the density value DX is read from the storage table 13 of the D - reading density corresponding value V. Thereby, in the CPU 12, the reading density corresponding value VX corresponding to the prescribed number NX of generating the dots is obtained. The obtained reading density corresponding value VX is used as the threshold.
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