Ms. Hanning Liang Profile

Hanning Liang

at Hochschule Fuer Angewandte Wissenschaften Landshut

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Publications (2)

Proceedings Article | 21 August 2020 Presentation + Paper

Using wavelet transform to evaluate single-shot phase measuring deflectometry data

Hanning Liang, Tomas Sauer, Christian Faber

Proceedings Volume 11510, 115101S (2020) https://doi.org/10.1117/12.2567301

KEYWORDS: Fringe analysis, Cameras, Wavelet transforms, Wavelets, Phase shifts, Deflectometry

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Phase measuring deflectometry (PMD) is a well-established method for determining the topography of specular freeform surfaces. A disadvantage of the classical PMD method, however, is the sequential measurement process - it requires at least six camera images of phase-shifted sinusoidal fringe patterns for one measurement. Therefore, for moving objects in industrial production, as well as for non-fixable objects such as the human cornea, the classical PMD evaluation is not suitable anymore. To overcome this problem, single-shot methods using single-side-band demodulation have been presented, which allow for a deflectometric measurement based on just one single image capture. However, this kind of evaluation does not work for complex surface geometries that result in broadband fringe patterns, since the phase is only considered globally in the Fourier space. A new single-shot evaluation method for the phase determination using the Continuous Wavelet Transform (CWT) is presented. The advantage of the wavelet transform is that the signal can be evaluated locally in both spatial and frequency space, making it possible to measure even complex reflective surfaces in motion. First measurement results are shown and compared to the classic phase-shifting evaluation for a non-moving object. Furthermore, limits and possible enhancements of this new method are discussed. Phase measuring deflectometry (PMD) is a well-established method for determining the topography of specular freeform surfaces. A disadvantage of the classical PMD method, however, is the sequential measurement process - it requires at least six camera images of phase-shifted sinusoidal fringe patterns for one measurement. Therefore, for moving objects in industrial production, as well as for non-fixable objects such as the human cornea, the classical PMD evaluation is not suitable anymore. To overcome this problem, single-shot methods using single-side-band demodulation have been presented, which allow for a deflectometric measurement based on just one single image capture. However, this kind of evaluation does not work for complex surface geometries that result in broadband fringe patterns, since the phase is only considered globally in the Fourier space. A new single-shot evaluation method for the phase determination using the Continuous Wavelet Transform (CWT) is presented. The advantage of the wavelet transform is that the signal can be evaluated locally in both spatial and frequency space, making it possible to measure even complex reflective surfaces in motion. First measurement results are shown and compared to the classic phase-shifting evaluation for a non-moving object. Furthermore, limits and possible enhancements of this new method are discussed.

Proceedings Article | 3 September 2019 Paper

A new method for solving the height problem in deflectometry

Hanning Liang, Alexander Zimmermann, Reiner Kickingereder, Christian Faber

Proceedings Volume 11102, 111020P (2019) https://doi.org/10.1117/12.2527747

KEYWORDS: Deflectometry, 3D metrology, Mirrors

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