FPP works on the same principle as stereo vision, where an object's coordinate in 3D space is derived by triangulating between pixels of two cameras. SLI avoids the computational complexities of matching pixels across camera views by replacing one of the two component cameras with a projector that generates a series of fringe patterns. By analyzing the change in the pattern at a particular point on the target object's surface a process known as phase demodulation and unwrapping of the captured fringes , unique correspondences can be derived between the camera and projector pixels.
However, traditional fringe projection profilometers are usually designed to measure static object shapes under non-time-critical measurement conditions, their measurement of moving objects is limited. Besides, it is difficult to retrieve the absolute phase for spatially isolated surfaces simultaneously and rapidly since in the phase unwrapping, fringe orders will be ambiguous, making the depth difference between spatially isolated surfaces indiscernible.
In this paper, we develop a computational framework to address the challenge. The proposed computational framework includes four major approaches to alleviate the harmonic error problem: i use more than one period of low-frequency patterns enabled by geometric constraint-based phase unwrapping method; ii artificially apply a large Gaussian filter to low frequency patterns before phase computation; iii create an error lookup table LUT to compensate for harmonic error; and iv develop a boundary error correction method to alleviate problems associated with filtering.
Both simulation and experimental results demonstrated the success of the proposed method. Chen and S. Zhang, "Three dimensional range geometry and texture data compression with space-filling curves," Opt. Express 25 21 , ; doi This paper presents a novel method to effectively store three-dimensional 3D data and 2D texture data into a regular bit image. The proposed method uses the Hilbert space-filling curve to map the normalized unwrapped phase map to two 8-bit color channels, and saves the third color channel for 2D texture storage.
By further leveraging existing 2D image and video compression techniques, the proposed method can achieve high compression ratios while effectively preserving data quality.
Since the encoding and decoding processes can be applied to most of the current 2D media platforms, this proposed compression method can make 3D data storage and transmission available for many electrical devices without requiring special hardware changes. Sheng, J. Xu, and S. However, fringe projection profilometry is prone to overexposure if objects have a wide range of reflectance. In this paper, we propose a dynamic projection theory based on fringe projection profilometry to rapidly measure the overexposed region with an attempt to conquer this challenge.
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This theory modifies the projected fringe image to the next better measurement based on the feedback provided by the previously captured image intensity. Experiments demonstrated that the number of overexposed points can be drastically reduced after one or two iterations. Compared with the state-of-the-art methods, our proposed dynamic projection theory measures the overexposed region quickly and effectively, and thus broadens the applications of fringe projection profilometry.
This paper proposes an absolute phase unwrapping method for 3D measurement that uses two cameras and one projector. On the left camera image, each pixel has one wrapped phase value which corresponds to multiple projector candidates with different absolute phase values.
High-Speed 3D Imaging with Digital Fringe Projection Techniques
We use geometric relationship of the system to map projector candidates into right camera candidates. By applying a series of candidate rejection criteria, a unique correspondence pair between two camera images can be determined. Then the absolute phase is obtained by tracing the correspondence point back to projector space. Experimental results demonstrate that the proposed absolute phase unwrapping algorithm can successfully work on both complex geometry and multiple isolated objects measurement. Li, T.
High-Speed 3D Imaging with Digital Fringe Projection Techniques (Opti…
Bell, and S. Yet, for many measurement conditions, such level of generality is inessential when having the pre-knowledge of object geometry. This paper introduces a novel adaptive algorithm for absolute 3D shape measurement with the assistance of the object CAD model. The proposed algorithm includes the following major steps: 1 export the 3D point cloud data from the CAD model; 2 transform the CAD model into the camera perspective; 3 obtain wrapped phase map from three phase-shifted fringe images; 4 retrieve absolute phase and 3D geometry assisted by CAD model.
We demonstrate that if object CAD models are available, such algorithm is efficient in recovering absolute 3D geometries of both simple and complex objects with only three phase-shifted fringe images. Hyun, B. Li, and S. Zhang, "High-speed high-accuracy three-dimensional shape measurement using digital binary defocusing method versus sinusoidal method," Opt.
This paper presents our research findings on high-speed high-accuracy 3D shape measurement using digital light processing DLP technologies. In particular, we compare two different sinusoidal fringe generation techniques using the DLP projection devices: direct projection of 8-bit computer generated sinusoidal patterns a. This paper mainly examines their performance on high-accuracy measurement applications under precisely controlled settings. Two different projection systems were tested in this study: the commercially available inexpensive projector, and the DLP development kit.
Experimental results demonstrated that the binary defocusing method always outperforms the sinusoidal method if a sufficient number of phase-shifted fringe patterns can be used. West Lafayette, Indiana. XYZT Lab. Current Members Alumni. Students Prof. Zhang Group. View Paper. Technical Paper. Abstract This paper presents our research findings on high-speed high-accuracy 3D shape measurement using digital light processing DLP technologies.
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- Unwrap phase!
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Google Scholar. Pan, P. Huang, and F. Guo, H. He, Y. Yu, and M. Zhang, X. Li, and S. Zhang and S. He, and M. Li, Y.