| 摘要 |
PURPOSE:To remarkably simplify a threshold deciding circuit, by reading out the threshold level corresponding to a notable picture element position from a memory after the level is once stored in the memory and correcting the level by moving it upward or downward by means of a level changing means in corresponding to the designation of the density at the time of reading an original. CONSTITUTION:A ROM 11 for outputting threshold level which inputs levels of picture elements P, Q, R, and S in the vicinity of a notable picture element A and decides at which threshold level the notable picture element is binary coded, is provided. The ROM 11 reads out the threshold level of the notable picture element A from the correlation among the picture elements P, Q, R, and S. With respect to the output of the ROM 11, the process of the density mode designated at the time of reading an original is performed by means of a density switching device 12 in such a way that, when the density mode is designated to 'dark', the threshold level is lowered and, when designated to 'light', the threshold level is raised. In other words, the threshold level is decided by means of the combination of the ROM 11 and switching device 12 and binary signals are produced after the threshold level is com pared with the notable picture element A at a comparator 13. Therefore, this circuit is made smaller in size and simpler in constitution. In addition, this circuit can be changed easily.
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