A simplified algorithm for digital fringe analysis in two-wave interferometry with sinusoidal phase modulation (original) (raw)
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Weighted averaging of a sequence of phase-shifted interference patterns yields a fringe-free intensity image that can be useful for machine vision, lateral metrology, defect detection, and other supplementary tasks in a surface-profiling interferometer. Coefficients for effective fringe-removal algorithms follow from a Fourier analysis of phase-shifting errors. Theoretical and experimental examples illustrate the substantially improved performance of a well-designed weighted average over a simple linear sum of data frames.
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A simple non-iterative algorithm for generalized phase-shifting interferometry is proposed. This algorithm recovers the wrapped phase from two or more interferograms with unknown phase steps between 0 and p rad. The proposal is based on the least squares method to calculate four parameters: background and modulation light, phase steps and wrapped phase distribution. This algorithm, by a new interferogram normalization procedure, can handle interferograms with variable spatiotemporal visibility overcoming the restriction and drawbacks from usual variable spatial visibility approaches. The algorithm works very well for processing interferograms which include many fringes. This behaviour will be explicated and discussed. The effectiveness and robustness of this algorithm are supported by numerical simulation and by the evaluation of experimental interferograms. The phaseshift estimation quality is verified by two different techniques. By the properties of this algorithm, such as the low computing time and free of user intervention, we believe it could be used in automatic realtime applications.
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Journal of the Optical Society of America A, 2016
Recovery of an unwrapped wavefront in phase-shifting interferometry is considered when the wavefront phase increments are determined between previous and subsequent fringe patterns as well as between adjacent pixels of the current fringe pattern. A parametric model of a three-dimensional interferometric signal and the recurrence processing algorithm in state space are utilized, providing an evaluation of an unwrapped wavefront phase at each phase shift step in dynamic mode. Estimates of the achievable accuracy and experimental results of the wavefront recovery are presented. Comparison with the conventional seven-frame phase-shifting algorithm, which is one of the most accurate, confirmed the high accuracy and noise immunity of the proposed method.
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A method of phase difference determination in interferomet~ is presented. In this method, the phase difference between two interferograms is determined by fringe pattern matching with subpixel accuracy. The signal-to-noise ratio is significantly improved due to the region-based fringe pattern matching and its effect of averaging noise. The experiment shows that this method is useful for the determination of phase difference between two equi-spaced fringe patterns, and it has the advantages of high precision of measurement and high resistance to noise.
Fourier Fringe Analysis with Improved Spatial Resolution
Applied Optics, 2003
The spatial resolution of the phase image derived from the interferogram by Fourier fringe analysis is limited by the necessity to isolate a first order in the Fourier plane. By use of the two complementary outputs of the interferometer, it is possible to eliminate the zero order and thus to improve the spatial resolution by a factor of approximately 2. The theory of this improvement is presented and confirmed experimentally.