Fast temporal phase unwrapping method for the fringe reflection technique based on the orthogonal grid fringes

Error self-correction method for phase jump in multi-frequency phase-shifting structured light

Among 3D measurement approaches, multi-frequency phase-shifting structured light has advantages such as high resolution and high sampling rate owing to its point-to-point calculation method. However, there is always phase jump in the measurement process, which greatly reduces measurement accuracy. This paper proposes an error self-correction method for phase jump based on the multi-frequency heterodyne approach. The method uses redundant measurement data to implement self-correction and does not require additional data acquisition steps. We perform both simulations and experiments using the proposed error self-correction method and the classical heterodyne approach to compare the results. The experiment results verify both the accuracy and suitability of the proposed method.

A morphology phase unwrapping method with one code grating

This paper presents a fast and robust phase unwrapping method with only one code grating, named the morphology phase unwrapping (MPU) method. Using mathematical morphology operations, more than 36 fringe orders can be obtained accurately from only one code grating rather than at least three code gratings. Comparison experiments demonstrate that MPU has the highest robustness with a high quality factor (Q > 99.9%) under different conditions. Fast-changing facial expressions are reconstructed, indicating potential applications in the fields of augmented reality and virtual reality.

Three-Dimensional Shape Measurements of Specular Objects Using Phase-Measuring Deflectometry

The fast development in the fields of integrated circuits, photovoltaics, the automobile industry, advanced manufacturing, and astronomy have led to the importance and necessity of quickly and accurately obtaining three-dimensional (3D) shape data of specular surfaces for quality control and function evaluation. Owing to the advantages of a large dynamic range, non-contact operation, full-field and fast acquisition, high accuracy, and automatic data processing, phase-measuring deflectometry (PMD, also called fringe reflection profilometry) has been widely studied and applied in many fields. Phase information coded in the reflected fringe patterns relates to the local slope and height of the measured specular objects. The 3D shape is obtained by integrating the local gradient data or directly calculating the depth data from the phase information. We present a review of the relevant techniques regarding classical PMD. The improved PMD technique is then used to measure specular objects having discontinuous and/or isolated surfaces. Some influential factors on the measured results are presented. The challenges and future research directions are discussed to further advance PMD techniques. Finally, the application fields of PMD are briefly introduced.

Superfast high-resolution absolute 3D recovery of a stabilized flapping flight process

Scientific research of a stabilized flapping flight process (e.g. hovering) has been of great interest to a variety of fields including biology, aerodynamics, and bio-inspired robotics. Different from the current passive photogrammetry based methods, the digital fringe projection (DFP) technique has the capability of performing dense superfast (e.g. kHz) 3D topological reconstructions with the projection of defocused binary patterns, yet it is still a challenge to measure a flapping flight process with the presence of rapid flapping wings. This paper presents a novel absolute 3D reconstruction method for a stabilized flapping flight process. Essentially, the slow motion parts (e.g. body) and the fast-motion parts (e.g. wings) are segmented and separately reconstructed with phase shifting techniques and the Fourier transform, respectively. The topological relations between the wings and the body are utilized to ensure absolute 3D reconstruction. Experiments demonstrate the success of our computational framework by testing a flapping wing robot at different flapping speeds.

Wavefront aberration metrology based on transmitted fringe deflectometry

A simple, precise, and innovative technique for wavefront aberration measurement is presented in this paper. This technique is based on transmitted fringe deflectometry (TFD) used to measure wavefront slope and wavefronts. The system measurement error when measuring wavefront aberration is analyzed, including the aberration of the reference wavefront caused by shape distribution and the tilt and decentration of the phase object. Based on this, the system error model is established, and the system error compensation method is also presented. In addition, the system parameters calibration method is discussed in detail. Simulation and experimental results show that the proposed TFD wavefront aberration measurement model can achieve high measurement accuracy.

Spatiotemporal three-dimensional phase unwrapping in digital speckle pattern interferometry

We propose a hybrid spatiotemporal three-dimensional phase unwrapping algorithm for use in digital speckle pattern interferometry (DSPI). The feature of the proposed algorithm is the integration of one-dimensional temporal and two-dimensional spatial phase unwrapping algorithms. By demodulating the phase on a single reference point or multiple reference points using temporal phase unwrapping and on each separated phase map region using spatial phase unwrapping, the DSPI with the spatiotemporal three-dimensional phase unwrapping algorithm can realize the measurement of dynamic absolute displacements and the determination of abrupt phase changes which are usually caused by object discontinuities. We demonstrate that the presented algorithm can overcome the drawbacks of the traditional spatial and temporal phase unwrapping algorithms.