| 摘要 |
PURPOSE:To realize an output of the picture information with high quality, by setting automatically an optimum threshold level at all times for an original of a low contrast and even for an original having high texture density and low density respectively. CONSTITUTION:The picture information given from a photoelectric transducer is amplified by an amplifier 1 to be sampled and held 2 and then digitized by an A/D converter 3 to be stored in a buffer 4 by an amount equivalent to a line. A microcomputer 5 supplies the picture information from the buffer 4 with each picture element. The picture information equivalent to a line is sorted into plural levels, and the emerging frequency is measured for each level to produce a histogram of the picture information equivalent to a line. This histogram is divided into a group A of the set value VTH or more and a group B of the value VTH or less, and the picture information level at which the emerging frequency of the groups A and B reach peaks P1 and P2 respectively is detected. Furthermore the picture information level at which the emerging frequency shows the minimum value is detected based on the section between the picture information levels showing the peaks P1 and P2. Thus the threshold level is defined to binary coding the picture information. |
