Defect detection method and defect detection circuit in printed matter inspection apparatus

摘要

PURPOSE:To detect precisely a defect such as low density or a small area, by a method wherein after a differential signal exceeding a reference signal of a picture is made a candidate signal for a defect to which a threshold value in relation to the defect is set up, only the candidate signal for the defect exceeding the threshold value is decided as a defect signal. CONSTITUTION:In a picture detecting part 1, a printed matter A is scanned in the direction meeting at right angles with a conveying direction I of the printed matter A by a line sensor camera B and taken in a picture memory C. Then when a picture signal of the taken in printed matter A is regarded as an inspected picture signal D, a differential picture signal F between the same and a premade reference pattern picture signal E is operated and inspection is performed. In this case, measuring operations each of an area and density are performed in a computor G and a decision table H is made. Then the differential signal exceeding the reference signal is made a candidate signal for the defect, to which threshold values in relation to linear defects generated in density and an area and in conveying direction of the printed matter are set up and only the candidate signal for the defect exceeding those threshold values is decided as the defect signal.