Segmentation of ultrasonic TOFD testing image based on watershed method

In order to identify the defect in the testing image obtained by the ultrasonic time of flight diffraction (TOFD) method, by analyzing the feature of the testing image, the automatic algorithm for image segmentation is studied, including image preprocessing and segmentation. The image preprocessing method is presented, which is based on the signal cross-correlation algorithm. Then the extraction of weld region based on the searching extreme points of signals is expressed. After that the watershed transform with the control marker is used to segment the preprocessed image, thereby the defect is extracted. Different ultrasonic TOFD testing images are segmented by the presented automatic image segmentation method. The results show that the signal cross-correlation algorithm basically suppresses the pattern distortion of the image and the extraction of weld region can reduce the calculation time of segmentation. Compared with the segmentation result by the threshold method, the presented automatic image segmentation method solves the identification of defect which is close to the lateral wave and the method also can be used for multiple defects identification.