Fisheye Lens Research Articles

Quantifying Night Sky Brightness as a Stressor for Coastal Ecosystems in Moreton Bay, Queensland

Growing light pollution is increasingly studied in terrestrial environments. However, research on night lights in coastal ecosystems is limited. We aimed to complement spaceborne remote sensing with ground-based hemispheric photos to quantify the exposure of coastal habitats to light pollution. We used a calibrated DSLR Canon camera with a fisheye lens to photograph the night sky in 24 sites in the rapidly developing area of Moreton Bay, Queensland, Australia, extracting multiple brightness metrics. We then examined the use of the LANcubeV2 photometer and night-time satellite data from SDGSAT-1 for coastal areas. We found that the skies were darker in less urbanized areas and on islands compared with the mainland. Sky brightness near the zenith was correlated with satellite observations only at a coarse spatial scale. When examining light pollution horizontally above the horizon (60–80° degrees below the zenith), we found that the seaward direction was brighter than the landward direction in most sites due to urban glow on the seaward side. These findings emphasize the importance of ground measurements of light pollution alongside satellite imagery. In order to reduce the exposure of coastal ecosystems to light pollution, actions need to go beyond sites with conservation importance and extend to adjacent urban areas.

Application of Single-Frequency Arbitrarily Directed Split Beam Metasurface Reflector in Refractive Index Measurements.

We present a sensor that utilizes a modified single-frequency split beam metasurface reflector to measure the refractive index of materials ranging from one to three. Samples are placed into a cavity between a PCB-etched dielectric and a reflecting ground plane. It is illuminated using a 10.525 GHz free-space transmit horn with reflecting angles measured by sweeping a receiving horn around the setup. Predetermined changes in measured angles determined through simulations will coincide with the material's index. The sensor is designed using the Fourier transform method of array synthesis and verified with FEM simulations. The device is fabricated using PCB milling and 3D printing. The quality of the sensor is verified by characterizing 3D printed dielectric samples of various infill percentages and thicknesses. Without changing the metasurface design, the sensing performance is extended to accommodate larger sample thicknesses by including a modified 3D printed fish-eye lens mounted in front of the beam splitter; this helps to exaggerate changes in reflected angles for those samples. All the methods presented are in agreement and verified with single-frequency index measurements using Snell's law. This device may offer a viable alternative to traditional index characterization methods, which often require large sample sizes for single-frequency measurements or expensive equipment for multi-frequency parameter extraction.

Vision-sharing system for android avatars to enable remote eye contact

Maintaining eye contact is a fundamental aspect of non-verbal communication, yet current remote communication tools, such as video calls, struggle to replicate the natural eye contact experienced in face-to-face interactions. This study presents a cutting-edge vision-sharing system for android avatars that enables remote eye contact by synchronizing the eye movements of the operator and the avatar. Our innovative system features an eyeball integrated with a wide-angle lens camera, meticulously designed to mimic human eyes in both appearance and functionality. This technology is seamlessly integrated into android avatars, enabling operators to perceive the avatar’s surroundings as if physically present. It provides a stable and immersive visual experience through a head-mounted display synchronized with the avatar’s gaze direction. Through rigorous experimental evaluations, we demonstrated the system’s ability to faithfully replicate the operator’s perspective through the avatar, making eye contact more intuitive and effortless compared with conventional methods. Subjective assessments further validated the system’s capacity to reduce operational workload and enhance user experience. These compelling findings underscore the potential of our vision-sharing system to elevate the realism and efficacy of remote communication using android avatars.

Robust calibration of surround-view camera systems with Planar-Eccentric Constraint: A novel Apriltag approach

This research tackles calibrating surround view camera systems for automated driving, where traditional methods require extensive manual measurements and precise conditions. We introduce a novel automatic calibration method that ensures portability and accuracy using only custom-designed calibration boards placed in the cameras’ common view. To address visual interference from extraneous objects, we design a unique board with AprilTag 2D codes, offering clear advantages over traditional checkerboards. Additionally, we’ve developed an Adaptive Angle Projection to counteract fisheye lens distortions. We also introduce a hierarchical pose optimization strategy that transitions from local to global, incorporating a “Planar-Eccentric constraint” to leverage the calibration board’s geometric positioning. Our method achieved 4.01 cm measurement error, with 0.075°angle error and 1.18 cm translation error. Our method’s efficacy and robustness were confirmed through extensive testing on an experimental vehicle and simulation dataset, proving its superiority in achieving precise calibration and measurement with minimal manual input.

Monitoring sedimentation of magnetorheological fluids using an infrared night vision wide-angle lens visual monitoring system with dynamic calibration method

Monitoring sedimentation of magnetorheological fluids using an infrared night vision wide-angle lens visual monitoring system with dynamic calibration method

Fisheye Night Sky Imager: A Calibrated Tool to Measure Night Sky Brightness

The Night Skies Team of the U.S. National Park Service (NPS) has developed a new camera system equipped with a fisheye lens to measure night sky brightness. This NPS Fisheye Night Sky Imager comprises a back-illuminated Sony IMX455 CMOS sensor housed in the ZWO ASI6200MM camera, a Johnson V filter, and a Sigma 8 mm F3.5 fisheye lens. All of the components are commercially available. The fisheye lens allows us to capture the entire sky in a single frame. The wide-angle view also introduces calibration challenges. To address this, we have customized tools and devised innovative methods for calibrating the system, including flat-field correction, pixel scale determination, and field of view characterization. Additionally, we use standard stars for precise positional and photometric calibration. Furthermore, we create an open-source Python pipeline to process these fisheye images and leverage Git and GitHub for source code version control and distribution. The resulting images provide a positionally and brightness-calibrated fisheye view of the night sky, with a photometric calibration uncertainty of 0.12 mag. When comparing our Fisheye Night Sky Imager measurements to images taken with other calibrated systems, we reliably achieve consistent results under both dark and bright skies. Our Fisheye Night Sky Imager not only enables rapid assessment of sky quality but also supports the feasibility of establishing permanent monitoring locations. Recognizing that the natural dark sky is a critical element for natural, cultural, educational, and visitor experiences, this new camera system enhances our ability to assess resource conditions and fulfill the NPS mission of conserving resources unimpaired for the enjoyment of this and future generations.

Wideband Multibeam Shared-Aperture Geodesic Half-Maxwell Fish-Eye Lens Antenna Based on 3-D Printed Technology for 5G Applications

Wideband Multibeam Shared-Aperture Geodesic Half-Maxwell Fish-Eye Lens Antenna Based on 3-D Printed Technology for 5G Applications

Automatic detection of color markings and numbers on trees in point clouds from Personal Laser Scanning (PLS) and Terrestrial Laser Scanning (TLS)

In forestry, colored spray paint is used for different purposes, such as marking trees that are chosen for the next harvest or that will be promoted by future silvicultural activities, or for the demarcation of skid/cable roads. Numerous studies have demonstrated the application of Terrestrial Laser Scanners (TLS) and Personal Laser Scanners (PLS) for the acquisition of tree parameters (diameters, heights, and tree positions) in a forest inventory context. However, no studies have included classification based on spectral information by applying colored markings to trees. When a laser scanner is combined with a camera, the color information can be mapped onto the laser point cloud, allowing for additional analysis of spectral information. In this study, we have tested the analysis of joint information from imagery and 3D point clouds in two different settings: (i) PLS point cloud data from a GeoSLAM ZEB Horizon were complemented with spectral information from images collected with a NCTech iSTAR Pulsar 360-degree camera, (ii) TLS point cloud data from a RIEGL VZ-400i were combined with imagery from a Nikon D850 digital single lens reflex (DSLR) camera with 14 mm fisheye lens. The major objective was to automatically classify trees that were marked with colored sprays automatically identify the numbers sprayed on the trees. The marked trees could be classified correctly with a balanced accuracy of 77.26% for PLS and 98.01% for the data collected with the TLS system using a support vector machine (SVM) model. The numbers written on the trees were classified from the TLS data using a YOLOv8 model. The accuracy of the digit classification reached up to 97.30%. In conclusion, it is possible to automatically detect marked trees and to automatically recognize the numbers spayed on these trees from colored point cloud data. However, accuracy strongly depends on the selected combination of scanner and camera. The findings of future research on this subject might differ with the ongoing development of PLS systems and could be enhanced by creating a large dataset of handwritten numbers collected using laser scanning systems.

Improving Otsu Method Parameters for Accurate and Efficient in LAI Measurement Using Fisheye Lens

The leaf area index (LAI) is an essential indicator for assessing vegetation growth and understanding the dynamics of forest ecosystems and is defined as the ratio of the total leaf surface area in the plant canopy to the corresponding surface area below it. LAI has applications for obtaining information on plant health, carbon cycling, and forest ecosystems. Due to their price and portability, mobile devices are becoming an alternative to measuring LAI. In this research, a new method for estimating LAI using a smart device with a fisheye lens (SFL) is proposed. The traditional Otsu method was enhanced to improve the accuracy and efficiency of foreground segmentation. The experimental samples were located in Gansu Ziwuling National Forest Park in Qingyang. In the accuracy parameter improvement experiment, the variance of the average LAI value obtained by using both zenith angle segmentation and azimuth angle segmentation methods was reduced by 50%. The results show that the segmentation of the front and back scenes of the new Otsu method is more accurate, and the obtained LAI values are more reliable. In the efficiency parameter improvement experiment, the time spent is reduced by 17.85% when the enhanced Otsu method is used to ensure that the data anomaly rate does not exceed 10%, which improves the integration of the algorithm into mobile devices and the efficiency of obtaining LAI. This study provides a fast and effective method for the near-ground measurement of forest vegetation productivity and provides help for the calculation of forest carbon sequestration efficiency, oxygen release rate, and forest water and soil conservation ability.

Monolithically Structured van der Waals Materials for Volume-Polariton Refraction and Focusing.

Polaritons, hybrid light and matter waves, offer a platform for subwavelength on-chip light manipulation. Recent works on planar refraction and focusing of polaritons all rely on heterogeneous components with different refractive indices. A fundamental question, thus, arises whether it is possible to configure two-dimensional monolithic polariton lenses based on a single medium. Here, we design and fabricate a type of monolithic polariton lens by directly sculpting an individual hyperbolic van der Waals crystal. The in-plane polariton focusing through sculptured step-terraces is triggered by geometry-induced symmetry breaking of momentum matching in polariton refractions. We show that the monolithic polariton lenses can be robustly tuned by the rise of van der Waals terraces and their curvatures, achieving a subwavelength focusing resolution down to 10% of the free-space light wavelength. Fusing with transformation optics, monolithic polariton lenses with gradient effective refractive indices, such as Luneburg lenses and Maxwell's fisheye lenses, are expected by sculpting polaritonic structures with gradually varied depths. Our results bear potential in planar subwavelength lenses, integrated optical circuits, and photonic chips.

Formation of a panoramic image of the inner surface of the pipe

Background. Visual non-destructive testing of the inner surface of pipes is an important aspect in their production and operation. A defect detected and corrected in a timely manner can significantly reduce the number of defects in production and prevent various emergency incidents during operation. Formation of a complete panoramic image of the inner surface of pipes suitable for quality analysis is an urgent and sought-after task that can be solved using computer vision systems. Aim. This work is the research and development of television methods for forming a complete panoramic image of the inner surface of a pipe, which can be analyzed to search for defects. Methods. To form a cylindrical panoramic image, mathematical models for the formation of an equidistant projection of spherical images obtained using a fisheye lens were used. For high-quality stitching of the resulting frames, digital image processing methods were used, including brightness and contrast transformations, and searching for special points using the MSER algorithm. Theoretical results are verified by full-scale modeling. Results. The result of this work is an algorithm for stitching frames of a video sequence generated by a television camera with a fisheye optical system, uniformly moved along the longitudinal axis of the pipe, into a single panoramic image of the internal surface. Conclusion. The algorithm ensures the formation of a high-quality image of a full panorama of the inner surface of the pipes with the absence of brightness artifacts.

Open-source and low-cost miniature microscope for on-site fluorescence detection

The development of a compact and affordable fluorescence microscope can be a formidable challenge for growing needs in on-site testing and detection of fluorescent labeled biological systems, especially for those who specialize in biology rather than in engineering. In response to such a situation, we present an open-source miniature fluorescence microscope using Raspberry Pi. Our fluorescence microscope, with dimensions of 19.2 × 13.6 × 8.2 cm3 (including the display, computer, light-blocking case, and other operational requirements), not only offers cost-effectiveness (costing less than $500) but is also highly customizable to meet specific application needs. The 12.3-megapixel Raspberry Pi HQ Camera captures high-resolution imagery, while the equipped wide-angle lens provides a field of view measuring 21 × 15 mm2. The integrated wireless LAN in the Raspberry Pi, along with software-controllable high-powered fluorescence LEDs, holds potential for a wide range of applications. This open-source fluorescence microscope offers biohybrid sensor developers a versatile tool to streamline unfamiliar mechanical design tasks and open new opportunities for on-site fluorescence detections.

Efficacy of a wearable night-vision aid in patients with concentric peripheral visual field loss: a randomized, crossover trial.

To investigate the efficacy of our wearable night-vision aid in patients with concentric peripheral visual field loss. Prospective, single blind, three-group, and three-period crossover clinical study. The study included patients with concentric peripheral visual field loss, a best-corrected visual acuity (decimal visual acuity) of 0.1 or higher in the better eye, and the presence of a central visual field. HOYA MW10 HiKARI® (HOYA Corporation), our original wearable night-vision aid, was used as the test device with three types of camera lenses (standard-, middle-, and wide-angle lenses). Under both bright and dark conditions, the angle of the horizontal visual field was measured using each of the three lens types for each group. The baseline angle was measured when each participant wore the night-vision aid (powered off). The study included 21 participants. Under bright condition, the perceived horizontal visual field was significantly wider than the baseline setup when using the standard-angle lens ("the standard lens"); the middle-angle lens ("the middle lens") was significantly wider than both the baseline setup and the standard lens; and the wide-angle lens ("the wide lens") was significantly wider than the other lenses. Under dark condition, the perceived horizontal visual field was again significantly wider when using the middle lens than the baseline setup and the standard lens, and when using the wide lens, the perceived horizontal visual field was again wider than when using the other lenses. The control in the bright condition was significantly wider (p < 0.001) than when used in the dark condition, while the standard-angle lens in the dark condition was significantly wider (p = 0.05) than when used in the bright condition. In regards to the middle and wide lenses, there was no statistically significant result emerging from either of the illumination conditions. Our wearable night-vision aid with a middle-angle or wide-angle lens appears to provide wider visual field images in patients with concentric peripheral visual field loss, regardless of whether the illumination conditions are bright or dark.

Unveiling New IoT Antenna Developments: Planar Multibeam Metasurface Half-Maxwell Fish-Eye Lens with Wavelength Etching

This study introduces a groundbreaking antenna system, the directive Metasurface Half-Maxwell Fish-Eye (MHMF) lens antenna, tailored specifically for Internet-of-Things (IoT) networks. Designed to operate at 60 GHz, this antenna ingeniously integrates a dipole antenna within a parallel-plate waveguide to illuminate a Half-Maxwell Fish-Eye (HMFE) lens. The HMFE lens serves as a focal point, enabling a crucial high gain for IoT operations. The integration of metasurface structures facilitates the attainment of the gradient refractive index essential for the lens surface. By employing commercial Ansys HFSS software, extensive numerical simulations were conducted to meticulously refine the design, focusing particularly on optimizing the dimensions of unit cells, notably the modified H-shaped cells within the parallel waveguides housing the beam launchers. A functional prototype of the antenna was constructed using a standard PCB manufacturing process. Rigorous testing in an anechoic chamber confirmed the functionality of these manufactured devices, with the experimental results closely aligning with the simulated findings. Far-field measurements have further confirmed the effectiveness of the antenna, establishing it as a high-gain antenna solution suitable for IoT applications. Specifically, it operates effectively within the 60 GHz range of the electromagnetic spectrum, which is crucial for ensuring reliable communication in IoT devices. The directive HMFE lens antenna represents a significant advancement in enhancing IoT connectivity and capabilities. Leveraging innovative design concepts and metasurface technology, it heralds a new era of adaptable and efficient IoT systems.

Continuous Leaf Area Index (LAI) Observation in Forests: Validation, Application, and Improvement of LAI-NOS

The leaf area index (LAI) is one of the core parameters reflecting the growth status of vegetation. The continuous long-term observation of the LAI is key when assessing the dynamic changes in the energy exchange of ecosystems and the vegetation’s response indicators to climate change. The errors brought about by non-standard operations in manual LAI measurements hinder the further research utilization of this parameter. The long-term automatic LAI observation network is helpful in reducing errors from manual measurements. To further test the applicability of automatic LAI observation instruments in forest environments, this study carried out comparative validation research of the LAI-NOS (LAI automatic network observation system) at the Wanglang Mountain Ecological Remote Sensing Comprehensive Observation Station, China, comparing it with the results measured by the LAI-2200 Plant Canopy Analyzer (LI-COR, Lincoln, NE, USA), the LAI-probe handheld instrument, and a fisheye lens digital camera (DHP method). Instead of using the original “smoothest window” method, a new method, the “sunrise–sunset” method, is used to extract daily LAI-NOS LAI, and the corresponding confidence level is used to filter the data. The results of the data analysis indicate the following: LAI-NOS has a high data stability. The automatically acquired daily data between two consecutive days has a small deviation and significant correlations. Single-angle/multi-angle LAI measurement results of the LAI-NOS have good correlations with the LAI-2200 (R2 = 0.512/R2 = 0.652), the LAI-probe (R2 = 0.692/R2 = 0.619), and the DHP method (R2 = 0.501/R2 = 0.394). The daily LAI obtained from the improved method, when compared to the original method, both show the same vegetation growth trend. However, the improved method has a smaller dispersion. This study confirms the stability and accuracy of automatic observation instruments in mountainous forests, demonstrating the distinct advantages of automatic measurement instruments in the long-term ground observation of LAIs.

Directional reflectance of light from landscapes on a long transect in Australia – forest to desert

The reflectance of land and vegetation observed in satellite imagery depends on sun and viewing geometry. This bidirectional reflectance requires correction for monitoring changes in vegetation cover and condition. We used a digital camera mounted in a light aircraft, and fitted with a fisheye lens, to measure directional reflectance of a diverse range of landscapes along a long transect in Australia — between Brisbane and the Simpson desert. All, except one, of the measured directional reflectances were able to be characterised accurately (adjusted r2 > 0.95) by the product of two analytical functions. The first, G(θ1,θ2), which represents volume scattering, is a function of illumination and viewing zenith angles, θ1andθ2, and has one parameter k:

Exploratory investigation of virtual lesions in gastrointestinal endoscopy using a novel phase‐shift method for three‐dimensional shape measurement

AbstractAccurate measurement of the size of lesions or distances between any two points during endoscopic examination of the gastrointestinal tract is difficult owing to the fisheye lens used in endoscopy. To overcome this issue, we developed a phase‐shift method to measure three‐dimensional (3D) data on a curved surface, which we present herein. Our system allows the creation of 3D shapes on a curved surface by the phase‐shift method using a stripe pattern projected from a small projecting device to an object. For evaluation, 88 measurement points were inserted in porcine stomach tissue, attached to a half‐pipe jig, with an inner radius of 21 mm. The accuracy and precision of the measurement data for our shape measurement system were compared with the data obtained using an Olympus STM6 measurement microscope. The accuracy of the path length of a simulated protruded lesion was evaluated using a plaster model of the curved stomach and graph paper. The difference in height measures between the measurement microscope and measurement system data was 0.24 mm for the 88 measurement points on the curved surface of the porcine stomach. The error in the path length measurement for a lesion on an underlying curved surface was &lt;1% for a 10‐mm lesion. The software was developed for the automated calculation of the major and minor diameters of each lesion. The accuracy of our measurement system could improve the accuracy of determining the size of lesions, whether protruded or depressed, regardless of the curvature of the underlying surface.

Retinal Image Quality Through an Operating Microscope With Wavefront Shaping Extended Depth of Focus Intraocular Lens in Model Eye

To compare the quality of images of gratings placed in a model eye viewed through an extended depth of focus (EDoF) intraocular lens (IOL) to that of diffractive bifocal IOL or monofocal IOL. Experimental laboratory investigation. Nondiffractive wavefront shaping EDoF (CNAET0, Alcon Laboratories), echelette-designed EDoF (ZXR00V, Johnson & Johnson Vision), diffractive bifocal IOL with low power addition (SV25T, Alcon Laboratories), or monofocal IOL (CNA0T0, Alcon Laboratories) was placed in a fluid-filled model eye. A United States Air Force Resolution Grating Target was glued to the posterior surface of the model eye and viewed through a flat or a wide-angle contact lens. The contrast of the gratings viewed through the EDoF or multifocal IOLs was compared to that through the monofocal IOL. A wavefront analyzer was used to measure the spherical power of the central 4.5 mm optics of the EDoF, multifocal, and monofocal IOLs. The distribution of the dioptric power and the dioptric power map were compared. The gratings observed through the flat contact lens with CNAET0, ZXR00V, or SV25T were slightly blurred when viewed through the multifocal optics. The blurred area was in the circumferential area of CNAET0, the central area of SV25T, and the peripheral area of ZXR00V. The mean contrast was 0.258 ± 0.020 for CNAET0, 0.227 ± 0.025 for ZXR00V, and 0.221 ± 0.020 for SV25T for the 16.0 cyc/mm grating. The contrast was significantly lower for ZXR00V (P = .004) and SV25T (P = .004) than 0.303 ± 0.015 for CNA0T0 but the differences were not significant for CNAET0. For the wide-angle contact lens, the contrast for CNAET0 was 0.182 ± 0.009, for ZXR00V was 0.162 ± 0.011, and for SV25T was 0.163 ± 0.007 for the 16.0 cyc/mm grating, and none was significantly different from 0.188 ± 0.012 for CNA0T0. The dioptric variations of CNAET0 indicated a ring-shaped area of higher power corresponding to the circumferential blurred zone observed through the flat contact lens. The wavefront shaping and echelette-designed EDoF-IOLs reduce the contrast of the grating more than the monofocal IOL when viewed through the flat contact lens. The degree of reduction depended on the design of the extended-focus optics. The difference was less through the wide-angle contact lens.

A CNN-LSTM model using elliptical constraints for temporally consistent sun position estimation

More accurate sun position estimation could transform the design and operation of solar power systems, weather forecasting services, and outdoor augmented reality systems. Although several image-based approaches to sun position estimation have been proposed, their performance is significantly affected by momentary disruptions in cloud cover because they use only a single image as input. This study proposes a deep learning-based sun position estimation system that leverages spatial, temporal, and geometric features to accurately regress sun positions even when the sun is partially or entirely occluded. In the proposed approach, spatial features are extracted from an input image sequence by applying a separate Resnet-based convolution network to each frame. To ensure that the temporal changes in the brightness distribution across frames are considered, the spatial features are concatenated and passed on to a stack of LSTM layers prior to regressing the final sun position. The proposed network is also trained with elliptical (geometric) constraints to ensure that predicted sun positions are consistent with the natural elliptical path of the sun in the sky. The proposed approach's performance was evaluated on the Sirta and Laval datasets along with a custom dataset, and an R2 Score of 0.98 was achieved, which is at least 0.1 higher than that of previous approaches. The proposed approach is capable of identifying the position of the sun even when occluded and was employed in a novel sky imaging system consisting of only a camera and fisheye lens in place of a complex array of sensors.

A photogrammetric approach for real‐time visual SLAM applied to an omnidirectional system

AbstractThe problem of sequential estimation of the exterior orientation of imaging sensors and the three‐dimensional environment reconstruction in real time is commonly known as visual simultaneous localisation and mapping (vSLAM). Omnidirectional optical sensors have been increasingly used in vSLAM solutions, mainly for providing a wider view of the scene, allowing the extraction of more features. However, dealing with unmodelled points in the hyperhemispherical field poses challenges, mainly due to the complex lens geometry entailed in the image formation process. To address these challenges, the use of rigorous photogrammetric models that appropriately handle the geometry of fisheye lens cameras can overcome these challenges. Thus, this study presents a real‐time vSLAM approach for omnidirectional systems adapting ORB‐SLAM with a rigorous projection model (equisolid‐angle). The implementation was conducted on the Nvidia Jetson TX2 board, and the approach was evaluated using hyperhemispherical images captured by a dual‐fisheye camera (Ricoh Theta S) embedded into a mobile backpack platform. The trajectory covered a distance of 140 m, with the approach demonstrating accuracy better than 0.12 m at the beginning and achieving metre‐level accuracy at the end of the trajectory. Additionally, we compared the performance of our proposed approach with a generic model for fisheye lens cameras.