"Adaptive focus stacking for large depth-of-field microscopic structured-light 3D imaging,” (2024)

[150] L. Chen, R. Ding and S. Zhang, “Adaptive focus stacking for large depth-of-field microscopic structured-light 3D imaging,” Applied Optics, (2024)

Abstract

This paper presents an adaptive focus stacking method for large depth-of-field (DOF) 3D microscopic structured-light imaging systems. Conventional focus stacking methods typically capture images under a series of pre-defined focus settings without considering the attributes of the measured object. Therefore, it is inefficient since some of the focus settings might be redundant. To address this problem, we first employ the focal sweep technique to reconstruct an initial rough 3D shape of the measured objects. Then, we leverage the initial 3D data to determine effective focus settings that focus the camera on the valid areas of the measured objects. Finally, we reconstruct a high-quality 3D point cloud using fringe images obtained from these effective focus settings by focus stacking. Experimental results demonstrate the success of the proposed method.

“Pixelwise calibration method for telecentric structured light system,” (2024)

Y. Yang and S. Zhang, “Pixelwise calibration method for telecentric structured light system,” Applied Optics, 63(10), (2024)

Abstract

This paper introduces a pixel-wise calibration method designed for a structured light system utilizing a camera attached with a telecentric lens. In the calibration process, a white flat surface and another flat surface with circle dots serve as the calibration targets. After deriving the properties of the pinhole projector through conventional camera calibration method using circle dots and determining the camera's attributes via 3D feature points estimation through iterative optimizations, the white surface calibration target was positioned at various poses and reconstructed with initial camera and projector calibration data. Each 3D reconstructions was fitted with an ideal virtual ideal plane that was further used to create the pixel-wise phase-to-coordinate mapping. To optimize the calibration accuracy, various angled poses of the calibration target are employed to refine the initial results. Experimental findings validate that the proposed approach offers high calibration accuracy for a structured light system using a telecentric lens.

“Unidirectional structured light system calibration with auxiliary camera and projector,” (2024)

Y. Yang, Y.-H. Liao, I. Bortins, D. P. Baldwin, and S. Zhang, “Unidirectional structured light system calibration with auxiliary camera and projector,” Optics and Lasers in Engineering, 175, 107984, (2024)

Abstract

This paper presents a novel calibration method for a unidirectional structured light system, which utilizes a white planar surface as the calibration target instead of the conventional targets with physical features like circle dots or checker squares. The proposed method reconstructs the white planar surface by employing stereo visionwith projected random patterns and plane fitting. To facilitate the calibration process, an auxiliary camera and an auxiliary projector are employed. Experimental results demonstrate that the high calibration accuracy is achieved by the proposed method for a unidirectional structured light system.

"Electrically tunable lens assisted absolute phase unwrapping for large depth-of-field 3D microscopic structured-light imaging,” (2024)

L. Chen and S. Zhang, “Electrically tunable lens assisted absolute phase unwrapping for large depth-of-field 3D microscopic structured-light imaging,” Optics and Lasers in Engineering, 174, 107967 (2024)

Abstract

This paper presents an absolute phase unwrapping method for large depth-of-field (DOF) microscopic structured-light 3D imaging. We calculate the wrapped phase maps and the fringe contrast maps from fringe images captured under various focus settings realized by an electrically tunable lens. From the fringe contrast maps, we extract each in-focus pixel and determine its approximate depth value from the focus settings. The approximate depth map is then used to create an artificial phase map. The geometric-constraint-based phase unwrapping method is adopted to unwrap the phase of all in-focus pixels using the artificial phase map. The unwrapped in-focus phase map is then used to reconstruct 3D coordinates for the entire DOF with the multi-focus pin-hole model. Experimental results demonstrate that our proposed method only requires three phase-shifted fringe patterns to achieve large DOF 3D imaging.