Complicated and time-consuming system calibration is indispensable for existing accurate three-dimensional reconstruction methods. To address this problem, this paper presents a simple and accurate optimized 3D reconstruction model based on a coaxial structured light system (CSLS). Compared to the traditional structured light system, CSLS contains a perspective projection unit and a telecentric imaging unit. Instead of obtaining the complicated structured light system parameters, the proposed model only requires the retrieval of a product matrix which could be easily calibrated by using an ordinary white plane. The influence of geometric distortion in the projector lenses has also been considered to further improve the measuring accuracy. Experiments were carried out to verify the validity of the proposed method.
This paper introduces a novel uniaxial fringe projection profilometry (FPP) called active shape from projection defocus profilometry (ASPDP), which utilizes the sharpness analysis of binary fringe patterns to quantify the defocus level. Compared with previous uniaxial FPP methods, our work first utilizes a pinhole defocus model to account for three-dimensional reconstruction. Since defocused fringe pattern can be modeled as the original pattern convoluted with a point spread function (PSF), pixel-wise defocus level can be quantified with this PSFs kernel using temporal Fourier analysis. In this research, calibration is achieved by using a mechanical translation device, and determined by rational polynomial fitting to establish defocus-depth relationship. The experiment demonstrates that this method can provide an accurate reconstructed 3D geometry without shadows.
Fringe projection technique has been widely used for three-dimensional (3D) shape measurement. However, it remains challenging to achieve high-speed measurement. A two-wavelength phase-shifting profilometry method with only four patterns is presented. Specifically, all these four patterns contain two wavelength components. The short wavelength component was used to compute the wrapped phase map, while the long one was used to unwrap the wrapped phase map. The performance of the proposed method was validated by both simulation study and experimental results.
This paper introduces a novel real-time high dynamic range 3D scanning method with RGB camera, which utilizes the cameras varying color sensitivity and the projector’s dark time to alleviate saturation-induced measurement error. The varying color responses in R, G, and B channels creates three different intensity levels, and an additional capture at the projectors bright to dark transition state doubles the total intensity levels to six. Finally, saturation-induced errors can be alleviated by choosing the unsaturated pixel of best quality among the images with six intensity levels. Experimental results will be presented to demonstrate the success of such method.
High-speed and high-accuracy three-dimensional (3D) measurement plays an important role in numerous areas. The recent proposed binary defocusing techniques have enabled the speed breakthrough by utilizing 1-bit binary fringe patterns with the advanced digital light processing (DLP) projection platform. To enhance the phase quality and measurement accuracy, extensive research has also been conducted to modulate and optimize the binary patterns spatially or temporally. However, it remains challenging for such techniques to measure objects with high dynamic range (HDR) of surface reflectivity. Therefore, to overcome this problem, this paper proposes a novel HDR 3D measurement method based on spectral modulation and multispectral imaging. By modulating the illumination light and acquiring the fringe patterns with a multispectral camera, high-contrast HDR fringe imaging and 3D measurement can be achieved. Experiments were carried out to demonstrate the effectiveness of the proposed strategy.
This research proposes a motion-induced error reduction method for phase shifting profilomtry. Particularly, each illuminated fringe pattern will be captured twice in one projection cycle when imaging a highly dynamic scene, resulting in two sets of phase shifted fringe images be obtained. A phase map will be computed for each phase shifting set in preparation for error analysis. Finally, motion-induced phase errors will be compensated by examining the difference of the two phase maps obtained respectively from two phase shifting sets. This method uses defocused 1-bit binary patterns to bypass rigid camera-projector synchronization, which has potential for high-speed applications.
Digital fringe projection technique is widely used for high-accuracy three-dimensional (3D) shape measurements. However, when the measured object is moving, there will be severe artifacts and phase errors induced by the movement even though a high-speed fringe projection system is used. Meanwhile, there are different kinds of motion such as uniform and non-uniform motion, which makes the problem even harder to address. To this end, this paper proposes a generic motion error compensation algorithm to deal with different motion artifacts. Both simulation and experiments demonstrated the proposed method can substantially reduce motion-induced measurement error.
For high-speed and high-accuracy 3D shape measurement, it has been demonstrated that using 1-bit binary patterns is advantageous over 8-bit sinusoidal phase-shifted fringe patterns especially on the digital-light-processing (DLP) projection platform. By properly defocusing the projector for specific square binary patterns, researchers have achieved the speed breakthroughs for high-accuracy 3D shape measurement, yet such a method requires carefully adjustment of the projector’s lens to within a small out-of-focus range, limiting its depth measurement capability. Optimizations based on pulse width modulation (PWM), optimal pulse width modulation (OPWM), and dithering/halftoning have substantially improved measurement quality, yet they only work well for a limited range of fringe period variations especially when a small number of phase-shifted fringe patterns are used. This paper proposes to generate high-quality phase using two sets of three phase-shifted binary patterns: the first set is generated by triangular pulse width modulation (TPWM) technique, and the second set being p shifted from the first set is also generated by TPWM technique. A three-step phase-shifting algorithm is then applied to compute the phase. Through optimizing the modulation frequency of the carrier signal, our simulation and experimental results demonstrate that high-quality phase can be generated for a wide range of fringe periods (e.g., from 18 to 1140 pixels) with only six binary patterns.
Digital-light-processing (DLP) and liquid-crystal-on-silicon (LCOS) are two digital projection technologies which enjoy
great popularity. This paper will demonstrate the performance of the two technologies in generating digital sinusoidal
fringe patterns in the two following ways: focused-sinusoidal-patterns (FSP) method and defocused-binary-patterns (DBP)
method. Experiment shows that for the FSP method, LCOS projector is a better choice since nonlinear gamma effect is less
significant and there is no need for precise synchronization; While for the DBP method, DLP projector has the advantage
over LCOS projector since the generated images have higher contrast ratio.
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