METHOD OF MAGNETO OPTIC IMAGE FEATURE EXTRACTION

A method of magneto optic imaging to locate the presence of a crack around a circular drilled bolt hole wherein the circular bolt hole, because of its sharp corners, locally disturbs the magnetic field used to form the image and obscures the presence of a crack therearound. Initially, a magneto optic image is formed of the drilled circular bolt hole under test, wherein a crack near the circular hole will perturb the circularity of the hole image by driving the magnetic field away from the circumference of the circular hole to cause it to appear out of round and eccentric. A pattern recognition analysis is then applied to the image to check the image for circular shapes, wherein each circular shape image is correlated with a circle of similar diameter to check the circularity of the image, and an eccentricity of the circular image shape is indicative of a crack around the drilled circular bolt hole. In greater detail, a computer program, in a bit by bit comparison, looks for differences in the diameter of the hole image which can be related to eccentricity, which is characteristic of a crack around the circular hole.