METHOD AND APPARATUS FOR SURFACE DEFECT INSPECTION

摘要

PURPOSE:To achieve highly accurate detection of the defects even when there is a trend in the intensity of an image signal about any of an unevenly colored defect, a defect due to a fine change in the surface roughness and a dot-like or linear fine defect. CONSTITUTION:Light irradiates the surface of a steel plate 26 from a light source 10 and the surface of the steel plate 26 is photographed with a TV camera 12 to transmit an image signal. The image signal is converted into digital with an A/D converter and the image signal converted is stored in a memory 20 while undergoing a specified image processing with an image processing section 18. The processing section 18 smoothes the image signal and an offset value is added evenly to the smoothed image signal to determine a threshold. A difference is determined between the original image signal and the threshold and a positive value of the difference is binary coded. The presence of a surface defect is judged from an area factor alpha of a dark part 32A of the binary coded signal. The results of the judgment are printed out from an outputting section 24 or shown on a monitor.