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1

One shot profilometry using iterative two-step temporal phase-unwrapping

Du G., Wang M., Zhou C., Si S., Li H., Lei Z., Li Y.

Optica Applicata

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2017

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Vol. 47, nr 1

97--110

EN

This paper reviews two techniques that have been recently published for three-dimensional profilometry and proposes one shot profilometry using iterative two-step temporal phase-unwrapping by combining the composite fringe projection and the iterative two-step temporal phase unwrapping algorithm. In temporal phase unwrapping, many images with different frequency fringe pattern are needed to project, which would take much time. In order to solve this problem, Ochoa proposed a phase unwrapping algorithm based on phase partitions using a composite fringe. However, we found that the fringe order determined through the construction of phase partitions tended to be imprecise. Recently, we proposed an iterative two-step temporal phase unwrapping algorithm, which can achieve high sensitivity and high precision shape measurement. But it needs multiple frames of fringe images which would take much time. In order to take into account both the speed and accuracy of three-dimensional shape measurement, we get a new, and more accurate unwrapping method based on a composite fringe pattern by combining these two techniques. This method not only retains the speed advantage of Ochoa’s algorithm, but also greatly improves its measurement accuracy. Finally, the experimental evaluation is conducted to prove the validity of the proposed method.

2

Improved method for phase wraps reduction in profilometry

Du G., Wang M., Zhou C., Si S., Li H., Lei Z., Li Y.

Optica Applicata

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2017

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Vol. 47, nr 2

295--306

EN

In order to completely eliminate, or greatly reduce the number of phase wraps in 2D wrapped phase map, Gdeisat and co-workers proposed an algorithm, which uses shifting the spectrum towards the origin. But the spectrum can be shifted only by an integer number, meaning that the phase wraps reduction is often not optimal. In addition, Gdeisat’s method will take much time to make the Fourier transform, inverse Fourier transform, select and shift the spectral components. In view of the above problems, we proposed an improved method for phase wraps elimination or reduction. First, the wrapped phase map is padded with zeros, the carrier frequency of the projected fringe is determined by high resolution, which can be used as the moving distance of the spectrum. And then realize frequency shift in spatial domain. So it not only can enable the spectrum to be shifted by a rational number when the carrier frequency is not an integer number, but also reduce the execution time. Finally, the experimental results demonstrated that the proposed method is feasible.

3

Optimizing the minimum cost flow algorithm for the phase unwrapping process in SAR radar

Dudczyk J., Kawalec A.

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2014

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Vol. 62, nr 3

511--516

EN

The last three decades have been abundant in various solutions to the problem of Phase Unwrapping in a SAR radar. Basically, all the existing techniques of Phase Unwrapping are based on the assumption that it is possible to determine discrete ”derivatives” of the unwrapped phase. In this case a discrete derivative of the unwrapped phase means a phase difference (phase gradient) between the adjacent pixels if the absolute value of this difference is less than π. The unwrapped phase can be reconstructed from these discrete derivatives by adding a constant multiple of 2π. These methods differ in that the above hypothesis may be false in some image points. Therefore, discrete derivatives determining the unwrapped phase will be discontinuous, which means they will not form an irrotational vector field. Methods utilising branch-cuts unwrap the phase by summing up specific discrete partial derivatives of the unwrapped phase along a path. Such an approach enables internally cohesive results to be obtained. Possible summing paths are limited by branch-cuts, which must not be intersected. These branch-cuts connect local discontinuities of discrete partial derivatives. The authors of this paper performed parametrization of the Minimum Cost Flow algorithm by changing the parameter determining the size of a tile, into which the input image is divided, and changing the extent of overlapping of two adjacent tiles. It was the basis for determining the optimum (in terms of minimum Phase Unwrapping time) performance of the Minimum Cost Flow algorithm in the aspect of those parameters.

4

Multi-STFT for adaptive SCPS phase determination

Sitnik R.

Opto-Electronics Review

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2009

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Vol. 17, No. 4

325-329

EN

This paper presents a fast and reliable approach for phase modulo 2π-calculation from a single fringe pattern. It calculates correct phase values even for very complex nd variable shape gradients based on a locally variable fringe period determined for the entire image. In the paper, a new two-step method for wrapped phase calculation is proposed. It is performed through the use of a method based on a multiple local fast Fourier transform for estimation of a local fringes period map and a 5-point spatial carrier phase shifting (SCPS) formula for phase modulo 2π-calculation. The described approach is verified by a correct demodulation of a real fringe pattern taken by a 3D-shape measurement system.

5

Automatyczna analiza prążków mory

Zawieska D., Podlasiak P.

Archiwum Fotogrametrii, Kartografii i Teledetekcji

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2000

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Vol. 10

66-1--66-10

PL

W referacie przestawiono doświadczenia autorów związane z odtwarzaniem kształtu powierzchni na podstawie analizy obrazów prążków mory. Do tych analiz zostało wykorzystane komputerowe stanowisko pomiarowe zaprojektowane dla potrzeb diagnostyki medycznej. Przeanalizowano dobór parametrów systemu optycznego generującego obraz mory oraz przedstawiono także wybrane metody odtworzenie informacji o analizowanej powierzchni na podstawie zarejestrowanego obrazu. Analiza prążków odbywa się w dwu etapach. Pierwszy związany jest z rejestracją kilku obrazów i jego celem jest wyznaczenie fazy prążka na podstawie jego jasności. Drugi etap ma na celu pozbycie się nieciągłości fazy, czyli wyznaczenia numeru prążka („phase unwarpping”). W niniejszym referacie omówiono także zjawisko pojawiające się, gdy powstający obraz prążków odbiega od teoretycznego modelu oraz próby wykorzystania analogii do obrazów radarowych SAR.