Detection of circular pattern in digital image

摘要

An image detecting method comprises the steps of: a) searching for a pattern satisfying a predetermined commencement requirement by scanning an input image; b) using the pattern as a starting point, with referring to a dictionary (4) storing therein distances between the center line and an edge of a detection target semicircle, determining for each of a predetermined number of main scan lines along a sub-scan direction whether or not a predetermined edge pattern occurs within a respective range of the distance of the dictionary; and c) determining a detection of the semicircle when the number of error lines on which the predetermined edge pattern does not occur within the respective range of the distance of the dictionary is less than a predetermined threshold.