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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Optical Sensors".

Deadline for manuscript submissions: closed (20 November 2023) | Viewed by 12882

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Special Issue Editors

Prof. Dr. Xiaowei Li

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Guest Editor

Department of Electronics and Information Engineering, Sichuan University, Chengdu 610065, China
Interests: 3D image encryption; watermarking; integral imaging; holography
Special Issues, Collections and Topics in MDPI journals

Dr. Han-Le Zhang

E-Mail Website
Guest Editor

School of Instrumentation Science and Optoelectronics Engineering, Beihang University, Beijing 100191, China
Interests: 3D display; integral imaging; autostereoscopic 3D display

Special Issue Information

Dear Colleagues,

New technologies for three-dimensional (3D) imaging and display, 3D security, and 3D interaction have been pursued by scientists and engineers for many decades. 3D imaging and display is very broad, and its application areas include education, medical treatment, manufacturing, augmented reality, interaction, security, etc. This Special Issue mainly looks at 3D imaging and display, integral imaging, holographic displays, autostereoscopic 3D display, 3D data security, and 3D interaction techniques with sensor technologies.

Integral imaging has advantages such as a continuous viewpoint, full parallax, no visual fatigue, and the fact that it is free for glasses, and it has been revived over the past decade or so as a promising approach for massive 3D commercialization. Holographic display is based on interference and diffraction of light to produce 3D images. The autostereoscopic 3D display employs a lenticular lens array to divide the 3D sources and rebuild the 3D images according to the binocular parallax principle. 3D display has been widely studied in many research fields, such as education, medical treatment, entertainment, etc. Three-dimensional data security is the process of protecting private data and preventing data loss through unauthorized access. Three-dimensional interaction technology is the use of somatosensory interaction sensors (such as Kinect, Leap Motion) to control 3D images. Therefore, this Special Issue aims to promote the development of 3D technologies, security, and interaction and encourage our colleagues to share and publish their research by submitting an academic paper.

Prof. Dr. Xiaowei Li
Dr. Han-Le Zhang
Guest Editors

Manuscript Submission Information

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Keywords

integral imaging
holographic displays
autostereoscopic 3D display
3D security
3D interaction techniques
3D imaging and display systems
holographic microcopy
data storage

Published Papers (10 papers)

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Research

11 pages, 784 KiB

Open AccessArticle

Speed Measurement of the Moving Targets Using the Stepping Equivalent Range-Gate Method

by Gang Yang, Zhaoshuo Tian, Zongjie Bi and Zihao Cui

Sensors 2024, 24(5), 1437; https://doi.org/10.3390/s24051437 - 23 Feb 2024

Viewed by 386

Abstract

In this paper, we proposed a stepping equivalent range-gate method (S-ERG method) to measure the speed and the distance of the moving target for range-gated imaging lidar. In this method, the speed is obtained by recording the time at which the moving target passes the front and back edges of the range gate, the distance information can also be obtained by the front and back edges of the range gate at the same time. To verify the feasibility of this method, a stationary target and a moving target with different speeds were measured by the S-ERG method. By using the S-ERG method, we not only obtained the distance information of the stationary target and the moving target at the front and back edges of the range gate, respectively, but also obtained the speed of the moving target. Compared to speeds measured by rotational displacement sensors, the speed measurement error of the S-ERG method is less than 5%, whether the target is far away or close to the range-gated lidar system, and this method is almost independent of the delay step time. The theoretical analysis and experimental results indicate range-gated imaging lidar using the S-ERG method has high practicality and wide applications. Full article

(This article belongs to the Special Issue Recent Advances in Optical Imaging and 3D Display Technologies)

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26 pages, 26563 KiB

Open AccessArticle

An Experimental Platform for Tomographic Reconstruction of Tissue Images in Brightfield Microscopy

by Panteleimon Koudounas, Efthymios Koniaris, Ioannis Manolis, Panteleimon Asvestas, Spiros Kostopoulos, Dionisis Cavouras and Dimitris Glotsos

Sensors 2023, 23(23), 9344; https://doi.org/10.3390/s23239344 - 23 Nov 2023

Viewed by 707

Abstract

(1) Background: Reviewing biological material under the microscope is a demanding and time-consuming process, prone to diagnostic pitfalls. In this study, a methodology for tomographic imaging of tissue sections is presented, relying on the idea that each tissue sample has a finite thickness and, therefore, it is possible to create images at different levels within the sample, revealing details that would probably not be seen otherwise. (2) Methods: Optical slicing was possible by developing a custom-made microscopy stage controlled by an ARDUINO. The custom-made stage, besides the normal sample movements that it should provide along the x-, y-, and z- axes, may additionally rotate the sample around the horizontal axis of the microscope slide. This rotation allows the conversion of the optical microscope into a CT geometry, enabling optical slicing of the sample using projection-based tomographic reconstruction algorithms. (3) Results: The resulting images were of satisfactory quality, but they exhibited some artifacts, which are particularly evident in the axial plane images. (4) Conclusions: Using classical tomographic reconstruction algorithms at limited angles, it is possible to investigate the sample at any desired optical plane, revealing information that would be difficult to identify when focusing only on the conventional 2D images. Full article

(This article belongs to the Special Issue Recent Advances in Optical Imaging and 3D Display Technologies)

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18 pages, 2241 KiB

Open AccessArticle

Hyperspectral Imaging with Active Illumination: A Theoretical Study on the Use of Incandescent Lamp and Variable Filament Temperature

by Urban Simoncic and Matija Milanic

Sensors 2023, 23(23), 9326; https://doi.org/10.3390/s23239326 - 22 Nov 2023

Viewed by 684

Abstract

In this study, we introduce a novel hyperspectral imaging approach that leverages variable filament temperature incandescent lamps for active illumination, coupled with multi-channel image acquisition, and provide a comprehensive characterization of the approach. Our methodology simulates the imaging process, encompassing spectral illumination ranging from 400 to 700 nm at varying filament temperatures, multi-channel image capture, and hyperspectral image reconstruction. We present an algorithm for spectrum reconstruction, addressing the inherent challenges of this ill-posed inverse problem. Through a rigorous sensitivity analysis, we assess the impact of various acquisition parameters on the accuracy of reconstructed spectra, including noise levels, temperature steps, filament temperature range, illumination spectral uncertainties, spectral step sizes in reconstructed spectra, and the number of detected spectral channels. Our simulation results demonstrate the successful reconstruction of most spectra, with Root Mean Squared Errors (RMSE) below 5%, reaching as low as 0.1% for specific cases such as black color. Notably, illumination spectrum accuracy emerges as a critical factor influencing reconstruction quality, with flat spectra exhibiting higher accuracy than complex ones. Ultimately, our study establishes the theoretical grounds of this innovative hyperspectral approach and identifies optimal acquisition parameters, setting the stage for future practical implementations. Full article

(This article belongs to the Special Issue Recent Advances in Optical Imaging and 3D Display Technologies)

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18 pages, 4619 KiB

Open AccessArticle

Design of a Two-Dimensional Conveyor Platform with Cargo Pose Recognition and Adjustment Capabilities

by Zhiguo Zhou, Hui Zhang, Kai Liu, Fengying Ma, Shijie Lu, Jian Zhou and Linhan Ma

Sensors 2023, 23(21), 8754; https://doi.org/10.3390/s23218754 - 27 Oct 2023

Viewed by 747

Abstract

Linear conveyors, traditional tools for cargo transportation, have faced criticism due to their directional constraints, inability to adjust poses, and single-item conveyance, making them unsuitable for modern flexible logistics demands. This paper introduces a platform designed to convey and adjust cargo boxes according to their spatial positions and orientations. Additionally, a cargo pose recognition algorithm that integrates image and point cloud data are presented. By aligning depth camera data, the axis-aligned bounding box (AABB) point serves as the image’s region of interest (ROI). Peaks extracted from the image’s Hough transform are refined using RANSAC-based point cloud linear fitting, then integrated with the point cloud’s oriented bounding box (OBB). Notably, the algorithm eliminates the need for deep learning and registration, enabling its use in rectangular cargo boxes of various sizes. A comparative experiment using accelerometer sensors for pose acquisition revealed a deviation of <0.7° between the two processes. Throughout the real-time adjustments controlled by the experimental platform, cargo angles consistently remained stable. The proposed two-dimensional conveyance platform, compared to existing methods, exhibits simplicity, accurate recognition, enhanced flexibility, and wide applicability. Full article

(This article belongs to the Special Issue Recent Advances in Optical Imaging and 3D Display Technologies)

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16 pages, 8481 KiB

Open AccessArticle

Generic and Model-Based Calibration Method for Spatial Frequency Domain Imaging with Parameterized Frequency and Intensity Correction

by Stefan A. Lohner, Steffen Nothelfer and Alwin Kienle

Sensors 2023, 23(18), 7888; https://doi.org/10.3390/s23187888 - 14 Sep 2023

Viewed by 959

Abstract

Spatial frequency domain imaging (SFDI) is well established in biology and medicine for non-contact, wide-field imaging of optical properties and 3D topography. Especially for turbid media with displaced, tilted or irregularly shaped surfaces, the reliable quantitative measurement of diffuse reflectance requires efficient calibration and correction methods. In this work, we present the implementation of a generic and hardware independent calibration routine for SFDI setups based on the so-called pinhole camera model for both projection and detection. Using a two-step geometric and intensity calibration, we obtain an imaging model that efficiently and accurately determines 3D topography and diffuse reflectance for subsequently measured samples, taking into account their relative distance and orientation to the camera and projector, as well as the distortions of the optical system. Derived correction procedures for position- and orientation-dependent changes in spatial frequency and intensity allow the determination of the effective scattering coefficient

μ_{s}^{'}

and the absorption coefficient

μ_{a}

when measuring a spherical optical phantom at three different measurement positions and at nine wavelengths with an average error of 5% and 12%, respectively. Model-based calibration allows the characterization of the imaging properties of the entire SFDI system without prior knowledge, enabling the future development of a digital twin for synthetic data generation or more robust evaluation methods. Full article

(This article belongs to the Special Issue Recent Advances in Optical Imaging and 3D Display Technologies)

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18 pages, 11467 KiB

Open AccessArticle

Confocal Laser Scanning Microscope Imaging of Custom-Made Multi-Cylinder Phantoms: Theory and Experiment

by David Hevisov, Felix Glöckler, Felix Ott and Alwin Kienle

Sensors 2023, 23(10), 4945; https://doi.org/10.3390/s23104945 - 21 May 2023

Viewed by 1870

Abstract

In this work, the image formation in a confocal laser scanning microscope (CLSM) is investigated for custom-made multi-cylinder phantoms. The cylinder structures were fabricated using 3D direct laser writing and consist of parallel cylinders with radii of 5 and 10

μ m

for [...] Read more.

μ m

for the respective multi-cylinder phantom, with overall dimensions of about

200 \times 200 \times 200 μ m^{3}

. Measurements were performed for different refractive index differences and by varying other parameters of the measurement system, such as pinhole size or numerical aperture (NA). For theoretical comparison, the confocal setup was implemented in an in-house developed tetrahedron-based and GPU-accelerated Monte Carlo (MC) software. The simulation results for a cylindrical single scatterer were first compared with the analytical solution of Maxwell’s equations in two dimensions for prior validation. Subsequently, the more complex multi-cylinder structures were simulated using the MC software and compared with the experimental results. For the largest refractive index difference, i.e., air as the surrounding medium, the simulated and measured data show a high degree of agreement, with all the key features of the CLSM image being reproduced by the simulation. Even with a significant reduction in the refractive index difference by the use of immersion oil to values as low as 0.005, a good agreement between simulation and measurement was observed, particularly with respect to the increase in penetration depth. Full article

(This article belongs to the Special Issue Recent Advances in Optical Imaging and 3D Display Technologies)

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16 pages, 5437 KiB

Open AccessArticle

Three Dimensional Shape Reconstruction via Polarization Imaging and Deep Learning

by Xianyu Wu, Penghao Li, Xin Zhang, Jiangtao Chen and Feng Huang

Sensors 2023, 23(10), 4592; https://doi.org/10.3390/s23104592 - 9 May 2023

Cited by 5 | Viewed by 1704

Abstract

Deep-learning-based polarization 3D imaging techniques, which train networks in a data-driven manner, are capable of estimating a target’s surface normal distribution under passive lighting conditions. However, existing methods have limitations in restoring target texture details and accurately estimating surface normals. Information loss can occur in the fine-textured areas of the target during the reconstruction process, which can result in inaccurate normal estimation and reduce the overall reconstruction accuracy. The proposed method enables extraction of more comprehensive information, mitigates the loss of texture information during object reconstruction, enhances the accuracy of surface normal estimation, and facilitates more comprehensive and precise reconstruction of objects. The proposed networks optimize the polarization representation input by utilizing the Stokes-vector-based parameter, in addition to separated specular and diffuse reflection components. This approach reduces the impact of background noise, extracts more relevant polarization features of the target, and provides more accurate cues for restoration of surface normals. Experiments are performed using both the DeepSfP dataset and newly collected data. The results show that the proposed model can provide more accurate surface normal estimates. Compared to the UNet architecture-based method, the mean angular error is reduced by 19%, calculation time is reduced by 62%, and the model size is reduced by 11%. Full article

(This article belongs to the Special Issue Recent Advances in Optical Imaging and 3D Display Technologies)

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13 pages, 3635 KiB

Open AccessCommunication

Synchronous Phase-Shifting Interference for High Precision Phase Imaging of Objects Using Common Optics

by Jiaxi Zhao, Lin Liu, Tianhe Wang, Xiangzhou Wang, Xiaohui Du, Ruqian Hao, Juanxiu Liu and Jing Zhang

Sensors 2023, 23(9), 4339; https://doi.org/10.3390/s23094339 - 27 Apr 2023

Viewed by 1138

Abstract

Quantitative phase imaging and measurement of surface topography and fluid dynamics for objects, especially for moving objects, is critical in various fields. Although effective, existing synchronous phase-shifting methods may introduce additional phase changes in the light field due to differences in optical paths or need specific optics to implement synchronous phase-shifting, such as the beamsplitter with additional anti-reflective coating and a micro-polarizer array. Therefore, we propose a synchronous phase-shifting method based on the Mach–Zehnder interferometer to tackle these issues in existing methods. The proposed method uses common optics to simultaneously acquire four phase-shifted digital holograms with equal optical paths for object and reference waves. Therefore, it can be used to reconstruct the phase distribution of static and dynamic objects with high precision and high resolution. In the experiment, the theoretical resolution of the proposed system was 1.064 µm while the actual resolution could achieve 1.381 µm, which was confirmed by measuring a phase-only resolution chart. Besides, the dynamic phase imaging of a moving standard object was completed to verify the proposed system’s effectiveness. The experimental results show that our proposed method is suitable and promising in dynamic phase imaging and measurement of moving objects using phase-shifting digital holography. Full article

(This article belongs to the Special Issue Recent Advances in Optical Imaging and 3D Display Technologies)

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11 pages, 3003 KiB

Open AccessCommunication

Deep Learning Enables Optofluidic Zoom System with Large Zoom Ratio and High Imaging Resolution

by Jiancheng Xu, Fenglin Kuang, Shubin Liu and Lei Li

Sensors 2023, 23(6), 3204; https://doi.org/10.3390/s23063204 - 17 Mar 2023

Cited by 3 | Viewed by 1387

Abstract

Due to the relatively low optical power of a liquid lens, it is usually difficult to achieve a large zoom ratio and a high-resolution image simultaneously in an optofluidic zoom imaging system. We propose an electronically controlled optofluidic zoom imaging system combined with deep learning, which achieves a large continuous zoom change and a high-resolution image. The zoom system consists of an optofluidic zoom objective and an image-processing module. The proposed zoom system can achieve a large tunable focal length range from 4.0 mm to 31.3 mm. In the focal length range of 9.4 mm to 18.8 mm, the system can dynamically correct the aberrations by six electrowetting liquid lenses to ensure the image quality. In the focal length range of 4.0–9.4 mm and 18.8–31.3 mm, the optical power of a liquid lens is mainly used to enlarge the zoom ratio, and deep learning enables the proposed zoom system with improved image quality. The zoom ratio of the system reaches 7.8×, and the maximum field of view of the system can reach ~29°. The proposed zoom system has potential applications in camera, telescope and so on. Full article

(This article belongs to the Special Issue Recent Advances in Optical Imaging and 3D Display Technologies)

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11 pages, 2973 KiB

Open AccessArticle

Phase Deflectometry for Defect Detection of High Reflection Objects

by Xian-Ming Cheng, Ting-Ting Wang, Wen-Bin Zhu, Bai-Di Shi and Wei Chen

Sensors 2023, 23(3), 1607; https://doi.org/10.3390/s23031607 - 1 Feb 2023

Cited by 2 | Viewed by 2309

Abstract

A method for detecting the surface defects of high reflection objects using phase deflection is proposed. The abrupt change in the surface gradient at the defect leads to the change in the fringe phase. Therefore, Gray code combined with a four-step phase-shift method was employed to obtain the surface gradients to characterize the defects. Then, through the double surface illumination model, the relationship between illumination intensity and phase was established. The causes of periodic error interference were analyzed, and the method of adjusting the fringe width to eliminate it was proposed. Finally, experimental results showed the effectiveness of the proposed method. Full article

(This article belongs to the Special Issue Recent Advances in Optical Imaging and 3D Display Technologies)

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