Application of S-transform profilometry in eliminating nonlinearity in fringe pattern

Area of Science:

• Optical metrology
• Signal processing
• 3D shape measurement

Background:

• The S-transform offers a powerful time-frequency analysis, extending short-time Fourier and wavelet transforms.
• Its application in optical 3D shape measurement using fringe projection is a recent development.
• Nonlinearity in fringe patterns poses challenges for accurate phase demodulation.

Purpose of the Study:

• To investigate the application of the S-transform for demodulating nonlinear fringe patterns.
• To develop and evaluate S-transform-based methods for eliminating phase errors in 3D measurements.

Main Methods:

• Introduced two S-transform-based methods: S-transform ridge method and S-transform filtering method.
• Theoretically detailed the application of these methods in fringe analysis.
• Validated methods through computer simulations and experimental verification.

Main Results:

• Both S-transform methods were employed to mitigate phase errors from projector and CCD nonlinearities.
• The S-transform filtering method demonstrated superior performance in reconstructing fringe patterns affected by nonlinearity.
• Results were compared against windowed Fourier transform, wavelet transform, and the S-transform ridge method.

Conclusions:

• The S-transform filtering method provides enhanced accuracy for 3D shape measurement with nonlinear fringe patterns.
• This study confirms the efficacy of S-transform techniques in addressing phase errors in optical metrology.
• The S-transform filtering method offers a significant improvement over existing reconstruction techniques under nonlinear conditions.