Error Model and Concise Temporal Network for Indirect Illumination in 3D Reconstruction.

3D reconstruction is a fundamental task in robotics and AI, providing a prerequisite for many related applications. Fringe projection profilometry is an efficient and non-contact method for generating 3D point clouds out of 2D images. However, during the actual measurement, it is inevitable to experiment with translucent objects, such as skin, marble, and fruit.

Accurate 3D Measurement of Complex Texture Objects by Height Compensation Using a Dual-Projector Structure.

Fringe projection profilometry is a widely used technique for 3D measurement due to its high accuracy and speed. However, the accuracy significantly decreases when measuring complex texture objects, especially in the junction of different colors. This paper analyzes the causes of errors resulting from complex textures and proposes a height compensation method to revise the error by employing a dual-projector structure.

On Boundary Discontinuity in Angle Regression Based Arbitrary Oriented Object Detection.

With vigorous development e.g., in autonomous driving and remote sensing, oriented object detection has gradually been featured.

Defocused projection model for phase-shifting profilometry with a large depth range.

Phase-shifting 3D profilometry is widely combined with defocused projection, but the accuracy of defocused projection could be far below expectations especially in the case of large depth range measurement. In this paper, a new defocus-induced error related to the shape of the measured object is pinpointed and a novel defocused projection model is established to cope with such a error to improve the accuracy of defocusing phase-shifting profilometry. Supplemented with a specialized calibration and reconstruction procedure, the phase is well corrected to obtain accurate measurement results.

Super-resolution technique for dense 3D reconstruction in fringe projection profilometry.

Fringe projection profilometry (FPP) is one of the most widely used 3D reconstruction techniques. A higher-resolution fringe pattern produces a more detailed and accurate 3D point cloud, which is critical for 3D sensing. However, there is no effective way to achieve FPP super-resolution except by using greater hardware.

Calibration for Camera-Projector Pairs Using Spheres.

A newly developed calibration algorithm for camera-projector system using spheres is presented in this paper. Previous studies have exploited image conics of sphere to calibrate the camera, whereas this approach can be strengthened to apply in the projector and ultimately achieve the overall calibration for single or multiple pairs of camera-projector. Following the concept of taking the projector as an inverse camera, we retrieve the image conic of the sphere on the projector plane based on a pole-polar relationship we found.

Research on a hole filling algorithm of a point cloud based on structure from motion.

A point cloud can be obtained from three-dimensional measurement reconstruction based on fringe projection. However, there are holes in a point cloud due to objects with complicated shapes and the defect of the method. The holes have a profound impact on the subsequent data processing.

Multiple-gamma-value based phase error compensation method for phase measuring profilometry.

Three-dimensional measurement based on fringe projection has been widely used. However, the gamma nonlinearity and system nonlinearities usually result in significant phase error. Furthermore, there are various gamma values due to the non-uniform brightness distribution of the projector and nonlinear factors of the system, which makes the problem more complicated.

Local blur analysis and phase error correction method for fringe projection profilometry systems.

We introduce a flexible error correction method for fringe projection profilometry (FPP) systems in the presence of local blur phenomenon. Local blur caused by global light transport such as camera defocus, projector defocus, and subsurface scattering will cause significant systematic errors in FPP systems. Previous methods, which adopt high-frequency patterns to separate the direct and global components, fail when the global light phenomenon occurs locally.

Bi-tangent line based approach for multi-camera calibration using spheres.

This paper presents a novel approach for multi-camera calibration using spheres. We determine the projection of sphere centers first through bi-tangent lines of projection conics, which provides another solution for camera parameters on the basis of the relationship between the images of spheres and the image of the absolute conic in dual space. All parameters are refined by an optimization with the purpose of minimizing the reprojection error, which is divided into two independent parts associated with the corresponding shape parameters of the conics.

Automatic fringe enhancement with novel bidimensional sinusoids-assisted empirical mode decomposition.

Fringe-based optical measurement techniques require reliable fringe analysis methods, where empirical mode decomposition (EMD) is an outstanding one due to its ability of analyzing complex signals and the merit of being data-driven. However, two challenging issues hinder the application of EMD in practical measurement. One is the tricky mode mixing problem (MMP), making the decomposed intrinsic mode functions (IMFs) have equivocal physical meaning; the other is the automatic and accurate extraction of the sinusoidal fringe from the IMFs when unpredictable and unavoidable background and noise exist in real measurements.

Ternary Gray code-based phase unwrapping for 3D measurement using binary patterns with projector defocusing.

The three-dimensional measurement technique using binary pattern projection with projector defocusing has become increasingly important due to its high speed and high accuracy. To obtain even faster speed without sacrificing accuracy, a ternary Gray code-based phase-unwrapping method is proposed by using even fewer binary patterns, which makes it possible to efficiently and accurately unwrap the phase. Theoretical analysis, simulations, and experiments are presented to validate the proposed method's efficiency and robustness.

Phase-shifting profilometry combined with Gray-code patterns projection: unwrapping error removal by an adaptive median filter.

Phase-shifting profilometry combined with Gray-code patterns projection has been widely used for 3D measurement. In this technique, a phase-shifting algorithm is used to calculate the wrapped phase, and a set of Gray-code binary patterns is used to determine the unwrapped phase. In the real measurement, the captured Gray-code patterns are no longer binary, resulting in phase unwrapping errors at a large number of erroneous pixels.

A Novel Camera Calibration Method Based on Polar Coordinate.

A novel calibration method based on polar coordinate is proposed. The world coordinates are expressed in the form of polar coordinates, which are converted to world coordinates in the calibration process. In the beginning, the calibration points are obtained in polar coordinates.

Novel 3D measurement system based on speckle and fringe pattern projection.

An efficient three-dimensional shape measurement system is proposed, which is based on the combining projection of single digital speckle pattern and phase-shifting fringe patterns. At the beginning, the initial corresponding point for each pixel is obtained by a novel speckle-phase combination method. The initial information can be calculated by the single speckle pattern in a short time, while the phase information is used to ensure the results.

Phase error analysis and compensation for phase shifting profilometry with projector defocusing.

Phase shifting profilometry (PSP) using binary fringe patterns with projector defocusing is promising for high-speed 3D shape measurement. To obtain a high-quality phase, the projector usually requires a high defocusing level, which leads to a drastic fall in fringe contrast. Due to its convenience and high speed, PSP using squared binary patterns with small phase shifting algorithms and slight defocusing is highly desirable.

Flexible calibration method for telecentric fringe projection profilometry systems.

A newly developed flexible calibration algorithm for telecentric 3D measurement systems is presented in this paper. We theoretically analyzed the similarities and differences between the telecentric and entocentric system. The telecentric system can be calibrated with the aid of the traditional 2D planar calibration method.

Differential signal-assisted method for adaptive analysis of fringe pattern.

In dynamic 3D measurements, the recovering carrier signal as well as phase retrieval are important issues for single fringe image analysis. Local mean decomposition is a powerful signal demodulation tool, but it usually encounters an obstacle, namely, the mode-mixing problem. Then different components, especially noise and carrier signals, are all probably mixed in one of the decomposition results, thus confusing its physical meaning.

Phase coding method for absolute phase retrieval with a large number of codewords.

A recently proposed phase coding method for absolute phase retrieval performs well because its codeword is embedded into phase domain rather than intensity. Then, the codeword can determine the fringe order for the phase unwrapping. However, for absolute phase retrieval with a large number of codewords, the traditional phase coding method becomes not so reliable.

Phase demodulation using adaptive windowed Fourier transform based on Hilbert-Huang transform.

The phase demodulation method of adaptive windowed Fourier transform (AWFT) is proposed based on Hilbert-Huang transform (HHT). HHT is analyzed and performed on fringe pattern to obtain instantaneous frequencies firstly. These instantaneous frequencies are further analyzed based on the condition of AWFT to locate local stationary areas where the fundamental spectrum will not be interfered by high-order spectrum.

Nonrigid-deformation recovery for 3D face recognition using multiscale registration.

Nonrigid deformation is a fundamental feature in face recognition. The proposed method extracts nonrigid deformation by finding the mapping between two shapes. To improve registration accuracy, it integrates geometric shape decomposition and nonrigid point-set registration.

Fringe image analysis based on the amplitude modulation method.

A novel phase-analysis method is proposed. To get the fringe order of a fringe image, the amplitude-modulation fringe pattern is carried out, which is combined with the phase-shift method. The primary phase value is obtained by a phase-shift algorithm, and the fringe-order information is encoded in the amplitude-modulation fringe pattern.

Flexible three-dimensional measurement technique based on a digital light processing projector.

A new method of 3D measurement based on a digital light processing (DLP) projector is presented. The projection model of the DLP projector is analyzed, and the relationship between the fringe patterns of the DLP and the fringe strips projected into the 3D space is proposed. Then the 3D shape of the object can be obtained by this relationship.