We implement a phase-shifting Talbot interferometric technique to measure step heights of a single-step and channel (dip) objects. Experimentally recorded interferograms include noise due to grating lines and speckles. To make the phase map, four interferograms are recorded with /2 phase shifts. To remove noise due to grating lines and speckle, interferogram data are first filtered using Fourier filtering. Height variations per profile of the objects is calculated from the phase map made using Fourier-filtered data. Results obtained from this technique are compared with the results acquired from a profile projector having a coordinate measurement facility with a resolution of 1 m and an accuracy of Ϯ1 m. The results are in good agreement.
A new filtering scheme is investigated for the removal of speckle noise in the recorded fringe pattern by a digital speckle pattern interferometric technique (DSPI). The scheme consists of a preprocessing scheme i.e., averaging, sampling, thresholding, and again averaging, followed either by a symlet or biorthogonal wavelet filter. The preprocessing scheme improves the contrast between the dark and bright fringes, and the implementation of the biorthogonal wavelet filter, which is symmetrical and purely linear in phase, solves the problem of border effect and discontinuity. The developed scheme is implemented on recorded fringe patterns of a vibrating cantilever beam and vibrating square plate with all ends fixed. The performance and effectiveness of the proposed scheme in reducing speckle noise is evaluated and compared in terms of reduction in speckle index and the improvement of the signal-to-noise ratio (SNR) of speckle interferograms. The new scheme has the ability to improve the speckle index and SNR significantly.Subject terms: digital speckle pattern interferometry; symlet wavelet filter; biorthogonal wavelet filter; speckle index; signal-to-noise ratio.
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