Real-time surface defects inspection of steel strip based on difference image

A method of difference image to inspect real-time defects for cold rolled steel strip is proposed, which is based on subtract arithmetic of image. That is, shooting a scene at different time subtraction or image of the same scene at different waveband subtraction. This paper outlines a subtraction operation between the gathering images and the standard images. The standard image selection utilizes sequence extraction technique, which is to extract background image as a standard image from the multi-frame continuous real-time processing of images, and the standard image is self adaptive update. In the course of image defect inspection, we divided the difference image into small regions and inspected them respectively with the character of defects being remarkable in part image. Through the experiment analysis, conditions can be obtained to judge if any defects exist. Experiment on five typical defects (wrinkles, inclusion, weld, holes and serrated edges) were done. The results show that this method can meet the requirements of defect inspection. and a higher rate of correct identification can be achieved.