A method based on the measurement of out-of-plane displacement by the phase-shifting digital speckle pattern interferometry is proposed to detect the edge of internal defects. The out-of-plane displacement is scanned by the scanning method of gradient streamlines first, which can provide paths through the defect edge with the best signal-to-noise ratio everywhere. Then, continuous wavelet transform (CWT) combined with the weighted structural intensity of the wavelet maxima is applied to detect the hidden singularities of the gradient streamlines that form the defect edge later. Moreover, the weighted structural intensity method is optimized to adapt to the detection of the hidden singularity by CWT. The results of theory, simulation, and experiments agree well, and the proposed method is efficient in internal defect detection.
An adaptive method is proposed in this paper for design of an ideal low-pass filter based on the Fourier-transform spectrum distribution of digital speckle interference fringe patterns. The size and shape of the ideal low-pass filter can be determined automatically by using an adaptive method based on the edge detection and morphological operation. The cutoff frequency of the ideal low-pass filter along arbitrary direction can also be determined automatically by using an adaptive method based on the Radon transform. The ideal low-pass filter designed in the paper can be used effectively for denoising of digital speckle interference fringe patterns in phase-shifting digital speckle pattern interferometry.
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