Dynamic classification of fringe patterns in holographic interferometry by optical wavelet filtering

摘要

In this paper the dynamic processing of interferometric fringe patterns obtained by real-time optical measurement methods like holographic interferometry is shown. A hologram of the tested component is superimposed with the hologram of the stressed component. The achieved fringe patterns vary according to the degree of stress applied. To evaluate these varying fringe patterns in real time, dynamic filtering is required. A hybrid opto-electronic system with a digital image processing and optical correlation module based on liquid-crystal spatial light modulators gives us the possibility to use dynamic filters and input images. In order to process interferometric fringes the adaptive wavelet transformation is applied. We will show two methods of dynamic filtering. Firstly a static filter is used to process varying fringe patterns. With this method changes of features in the fringe patterns can be observed correlating to changes of stress applied on the tested component. Another application of dynamic filtering uses a static input image and dynamic filters. This method is used for the classification of interferometric fringe patterns. A set of different wavelet filters is applied to the input image using the ability of the spatial light modulator to display images in video frame rates. Comparing the wavelet filters and the output images it is possible to assign the fringe patterns to a fault class.