| 摘要 |
PURPOSE:To attain automatic setting of binary-coded threshold value efficiently and properly even when background density changes by smoothing a picture data, deciding a film density corresponding to a minimum value of background and setting an optimum threshold value based on the obtained background density. CONSTITUTION:When a digital picture data is inputted to a low pass filter 606, the data is smoothed and outputted as a picture data. The picture data is a smoothed data of dust, flaw and background noise component, a minimum value L is found out by a minimum hold circuit, where the value is held, a multiplexer 610 is switched by a selection signal from a CPU 182 of a control section 180 and sent to the CPU 602 of the next stage. A density corresponding to the minimum value is stored in advance in the CPU 602, the corresponding density is read by the input of the minimum value and an optimum threshold level to the density is outputted from the read density and the result is applied to a comparator 604.
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