Absolute Phase - Explore the Science & Experts | ideXlab

Scan Science and Technology

Contact Leading Edge Experts & Companies

Absolute Phase

The Experts below are selected from a list of 61191 Experts worldwide ranked by ideXlab platform

Absolute Phase – Free Register to Access Experts & Abstracts

Song Zhang – One of the best experts on this subject based on the ideXlab platform.

  • Pixel-by-pixel Absolute Phase retrieval assisted by an additional three-dimensional scanner.
    Applied optics, 2019
    Co-Authors: Song Zhang
    Abstract:

    This paper presents a novel Absolute Phase unwrapping method assisted by a low-cost three-dimensional (3D) scanner. The proposed Absolute Phase unwrapping method leverages a low-cost 3D scanner to capture rough 3D data of the scene and transforms the rough 3D data to the world coordinate system to generate an artificial reference Phase map ϕ ref . By referring to ϕ ref , we can do Absolute Phase unwrapping directly without projecting any additional patterns, such that the digital fringe projection (DFP) system can achieve higher measurement speed. We develop a multiresolution system consisting of a DFP system and a Kinect V2 to validate our method. Experiments demonstrate that our method works for a large depth range, and the speed of the low-cost 3D scanner is not necessarily the maximum speed of our proposed method. Assisted by the Kinect V2, whose maximum speed is only 30 Hz, our DFP system achieves 53 Hz with a resolution 1600×1000 pixels when we measure dynamic objects that are moving in a large depth range of 400 mm.

  • Absolute Phase retrieval methods for digital fringe projection profilometry a review
    Optics and Lasers in Engineering, 2018
    Co-Authors: Song Zhang
    Abstract:

    Abstract This paper provides a review for Absolute Phase recovery methods that are applicable for digital fringe projection (DFP) systems. Specifically, we present two conventional Absolute Phase unwrapping methods: multi-frequency or –wavelength Phase-shifting methods, and hybrid binary coding and Phase-shifting methods; and also introduce some non-conventional methods that are specific for DFP systems: multiview geometry methods with additional camera(s) or projector(s), DFP system geometric constraint-based Phase unwrapping method, and pre-knowledge (e.g., computer-aided-design, CAD, model) based Phase unwrapping method. This paper also briefly overviews hybrid methods including Phase coding, composite, and pre-defined markers based Absolute Phase unwrapping methods. This paper explains the principle behind each individual Absolute Phase unwrapping method; and finally offers some practical tips to handle common Phase unwrapping artifact issues.

  • Absolute Phase unwrapping for dual-camera system without embedding statistical features
    Optical Engineering, 2017
    Co-Authors: Chufan Jiang, Song Zhang
    Abstract:

    This paper proposes an Absolute Phase unwrapping method for three-dimensional 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. We use the geometric relationship of the system to map projector candidates into the 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 the projector space. Experimental results demonstrate that the proposed Absolute Phase unwrapping algorithm can successfully work on both complex geometry and multiple isolated objects measurement.

Wilhelm Becker – One of the best experts on this subject based on the ideXlab platform.

Bo Tao – One of the best experts on this subject based on the ideXlab platform.

  • Stereo calibration with Absolute Phase target.
    Optics express, 2019
    Co-Authors: Yuwei Wang, Yajun Wang, Lu Liu, Bolin Cai, Keyi Wang, Xiangcheng Chen, Bo Tao
    Abstract:

    Stereo cameras have been widely used for three-dimensional (3D) photogrammetry, and stereo calibration is a crucial process to estimate the intrinsic and extrinsic parameters. This paper proposes a stereo calibration method with Absolute Phase target by using horizontal and vertical Phase-shifting fringes. The one-to-one mapping from the world points to the image points that can be recovered by referring to the Absolute Phase and then used to calibrate the stereo cameras. Compared with traditional methods that only use feature points within the overlapping field-of-view (FOV), the proposed method can use all feature points within the overlapping and non-overlapping FOVs. Besides, since Phase is more robust against camera defocusing than intensity, the target images can be captured regardless of the depth-of-field (DOF). With the advantages of whole-field capability and defocusing tolerability, the target placement becomes very flexible. Both simulations and experiment results demonstrate the robustness and accuracy of the proposed method.

  • Absolute Phase Retrieval Using One Coded Pattern and Geometric Constraints of Fringe Projection System
    Applied Sciences, 2018
    Co-Authors: Chunnian Zeng, Bo Tao, Jie Luo, Chen Xiangcheng
    Abstract:

    Fringe projection technologies have been widely used for three-dimensional (3D) shape measurement. One of the critical issues is Absolute Phase recovery, especially for measuring multiple isolated objects. This paper proposes a method for Absolute Phase retrieval using only one coded pattern. A total of four patterns including one coded pattern and three Phase-shift patterns are projected, captured, and processed. The wrapped Phase, as well as average intensity and intensity modulation, are calculated from three Phase-shift patterns. A code word encrypted into the coded pattern can be calculated using the average intensity and intensity modulation. Based on geometric constraints of fringe projection system, the minimum fringe order map can be created, upon which the fringe order can be calculated from the code word. Compared with the conventional method, the measurement depth range is significantly improved. Finally, the wrapped Phase can be unwrapped for Absolute Phase map. Since only four patterns are required, the proposed method is suitable for real-time measurement. Simulations and experiments have been conducted, and their results have verified the proposed method.

Yajun Wang – One of the best experts on this subject based on the ideXlab platform.

  • Stereo calibration with Absolute Phase target.
    Optics express, 2019
    Co-Authors: Yuwei Wang, Yajun Wang, Lu Liu, Bolin Cai, Keyi Wang, Xiangcheng Chen, Bo Tao
    Abstract:

    Stereo cameras have been widely used for three-dimensional (3D) photogrammetry, and stereo calibration is a crucial process to estimate the intrinsic and extrinsic parameters. This paper proposes a stereo calibration method with Absolute Phase target by using horizontal and vertical Phase-shifting fringes. The one-to-one mapping from the world points to the image points that can be recovered by referring to the Absolute Phase and then used to calibrate the stereo cameras. Compared with traditional methods that only use feature points within the overlapping field-of-view (FOV), the proposed method can use all feature points within the overlapping and non-overlapping FOVs. Besides, since Phase is more robust against camera defocusing than intensity, the target images can be captured regardless of the depth-of-field (DOF). With the advantages of whole-field capability and defocusing tolerability, the target placement becomes very flexible. Both simulations and experiment results demonstrate the robustness and accuracy of the proposed method.

  • Modified Gray-Level Coding Method for Absolute Phase Retrieval.
    Sensors (Basel Switzerland), 2017
    Co-Authors: Xiangcheng Chen, Yajun Wang, Yuwei Wang, Shunping Chen, Jie Luo, Lei Chen
    Abstract:

    Fringe projection systems have been widely applied in three-dimensional (3D) shape measurements. One of the important issues is how to retrieve the Absolute Phase. This paper presents a modified gray-level coding method for Absolute Phase retrieval. Specifically, two groups of fringe patterns are projected onto the measured objects, including three Phase-shift patterns for the wrapped Phase, and three n-ary gray-level (nGL) patterns for the fringe order. Compared with the binary gray-level (bGL) method which just uses two intensity values, the nGL method can generate many more unique codewords with multiple intensity values. With assistance from the average intensity and modulation of Phase-shift patterns, the intensities of nGL patterns are normalized to deal with ambient light and surface contrast. To reduce the codeword detection errors caused by camera/projector defocus, nGL patterns are designed as n-ary gray-code (nGC) patterns to ensure that at most, one code changes at each point. Experiments verify the robustness and effectiveness of the proposed method to measure isolated objects with complex surfaces.

  • quantized Phase coding and connected region labeling for Absolute Phase retrieval
    Optics Express, 2016
    Co-Authors: Xiangcheng Chen, Yajun Wang, Yuwei Wang, Chunnian Zeng
    Abstract:

    This paper proposes an Absolute Phase retrieval method for complex object measurement based on quantized Phase-coding and connected region labeling. A specific code sequence is embedded into quantized Phase of three coded fringes. Connected regions of different codes are labeled and assigned with 3-digit-codes combining the current period and its neighbors. Wrapped Phase, more than 36 periods, can be restored with reference to the code sequence. Experimental results verify the capability of the proposed method to measure multiple isolated objects.

Dejan B. Milošević – One of the best experts on this subject based on the ideXlab platform.

  • Metering the Absolute Phase of a few-cycle pulse via its high-order above-threshold ionization spectrum
    Laser Physics Letters, 2004
    Co-Authors: Dejan B. Milošević, G G Paulus, Wilhelm Becker
    Abstract:

    The influence of the carrier-envelope Phase (“Absolute Phase”) of a few-cycle pulse on the left-right asymmetry of the photoelectron spectrum of high-order above-threshold ionization is analyzed. Energy spectra are calculated for opposite detectors along the polarization axis of a linearly polarized four-cycle laser pulse. The results obtained allow us to determine the value of the Absolute Phase in a given experiment by comparison with the theoretical spectra. A classical analysis of the calculated spectra is presented, and the corresponding electron trajectories are analyzed. Emission of high-energy electrons is found to occur in one or two ultrashort subfemtosecond bursts.

  • Above-threshold ionization with few-cycle laser pulses and the relevance of the Absolute Phase
    Laser Physics, 2003
    Co-Authors: Dejan B. Milošević, G G Paulus, Wilhelm Becker
    Abstract:

    In a recent ‘stereo above-threshold ionization experiment, the influence of the Absolute Phase (the Phase of the carrier wave with respect to the laser-pulse envelope) on the left-right asymmetry of the emitted photoelectrons ionized by a few-cycle pulse was analyzed. Two detectors were used, positioned opposite each other in a plane perpendicular to the propagation direction of the laser beam. Depending on the value of the Absolute Phase, one detector registers more electrons than the other. Applying the Keldysh theory of above-threshold ionization, adjusted to the case of few-cycle pulses, we explore this left-right asymmetry in more detail. We investigate the AbsolutePhase dependence of the differential ionization probabilities and explain it using the saddle-point method. A theoretical analysis of the experiment, based on a correlation technique, is presented. The time dependence of the laser-field intensity of a few-cycle laser pulse is analyzed both for circular and for linear polarization.

  • High-order above-threshold ionization with few-cycle pulse: a meter of the Absolute Phase
    Optics express, 2003
    Co-Authors: Dejan B. Milošević, G. G. Paulus, Wilhelm Becker
    Abstract:

    Angle-resolved energy spectra of high-order above-threshold ionization are calculated in the direction of the laser polarization for a linearly polarized four-cycle laser pulse (two cycles FWHM) as a function of the carrier-envelope relative Phase (Absolute Phase). The spectra exhibit a characteristic left-right (backward-forward) asymmetry, which should allow one to determine the value of the Absolute Phase in a given experiment by comparison with the theoretical spectra. A classical analysis of the spectra calculated is presented. High-energy electron emission is found to occur in one or two ultrashort (< inverted exclamation mark