JPS57174776A - Threshold device - Google Patents

Abstract

PURPOSE:To set the optimum threshold level even in an original with low contrast or an original having high texture concentration and to output the picture information of high quality, by setting automatically the threshold level in accordance with the original. CONSTITUTION:Maximum value detecting circuits 8a and 8b detect the maximum values P1 and P2 of the emerging frequency for each level of the picture element information stored in memories 7a and 7b respectively. Address detecting circuits 9a and 9b detect the level of the picture element information showing the values P1 and P2. An arithmetic circuit 10 calculates the mean value of two pairs of picture information levels detected by the circuits 9a and 9b and feeds the mean value to a comparator 11 in the form of a threshold level. The picture element information equivalent to a line and fed from a buffer 6 is transferred to a buffer 12 to be delayed and furthermore transferred to the comparator 11 to be binary coded with the corresponding threshold level of the circuit 10.