Segmentation of small defects in a variable grey-grade image based on wavelet transformation and morphology filtering

Abstract

In this paper, the X-ray non-destructive testing method for the detection of small defects in laser weldments of titanium alloy with complex structure is presented. To resolve the difficulty of segmentation of small defects in a variable grey-grade image with low contrast and to improve the processing effects and speed, the methods of image processing based on wavelet transformation and morphology filtering were adopted. After the superimposition de-noising was adopted to remove the impulse noises, wavelet transformation was used to eliminate the residual noise for better resolution in both time domain and frequency domain. At the same time, one-dimensional morphology filtering was carried out to simulate the background, and the small defects in a variable grey-grade image with low contrast can be segmented. The experimental results show that the method can not only extract the small defects in a variable grey-grade image with low contrast, but can also improve the image processing speed, and the morphology of small defects can also be retained. This will provide a good basis for the quantitative research concerned with detecting small defects in variable grey-grade images with low contrast.