Applied Study Of Filtering Method For Electronic Speckle Pattern Interferometry Fringes Patterns And Phase Patterns

Electronic speckle pattern interferometry (ESPI) is a nondestructive, whole-field optical measurement technique. It is a well-known technique for deformed and nondestructive measurement of optical coarse surface. Accurate extraction of phase value is of fundamental importance for the successful application of ESPI in obtaining of the displacement. However, generally the resulting phase patterns are very noisy. Therefore, the phase pattern filtering method is very important to obtain precisely displacement information. In this paper, we put emphasis on discussing the filtering algorithm for fringes patterns and phase patterns.First, we apply the improved PDE image filtering methods to the ESPI fringe patterns. Then, according to the property of ESPI phase fringe pattern, we should reduce noise as well as preserve the phase jump in the filtering process. We apply the improved PDE image filtering methods to the ESPI phase patterns combined with the sine/cosine filtering method.The idea of Least-squares fitting is added to filtering method for phase pattern, and an effective filtering method is presented- The tangent Least-squares fitting filtering method. The improved filtering method has three advantages. First, this method has good applicability, it is suitable for all phase maps obtained by any technique; Second, this method can be repeated according to the noise level; Third, according to the shape of fringes, the small filtering window can be either rectangle or square along vertical direction. To obtaining better filtering effect, we establish filtering windows along the tangent direction of phase fringe pattern for dense fringes. For the phase patterns with sparse fringes, serial processing can be taken: for a picture of image, the calculation is carried out pixel-by-pixel, and the phase value of current pixel in original image renew immediately. The adoption of serial processing can improve the smoothing efficiency. The validity of the method is demonstrated and it is valuable for ESPI phase patterns.