Fisheye Lens Research Articles

Wide-angle concentric mirror lens objective

A new optical system of a wide-angle concentric isochromatic mirror–lens objective with a real image is presented and analyzed. The conditions for its isochromatic correction are obtained. The practical implementation of the objective is described.

Fall-to-the-centre as a symmetry breaking transition

The attractive inverse square potential arises in a number of physical problems such as a dipole interacting with a charged wire, the Efimov effect, the Calgero-Sutherland model, near-horizon black hole physics and the optics of Maxwell fisheye lenses. Proper formulation of the inverse-square problem requires specification of a boundary condition (regulator) at the origin representing short-range physics not included in the inverse square potential and this generically breaks the Hamiltonian’s continuous scale invariance in an elementary example of a quantum anomaly. The system’s spectrum qualitatively changes at a critical value of the inverse-square coupling, and we here point out that the transition at this critical potential strength can be regarded as an example of a symmetry breaking transition. In particular, we use point particle effective field theory (PPEFT), as developed by Burgess et al [1], to characterize the renormalization group (RG) evolution of the boundary coupling under rescalings. While many studies choose boundary conditions to ensure the system is unitary, these RG methods allow us to systematically handle the richer case of nonunitary physics describing a source or sink at the origin (such as is appropriate for the charged wire or black hole applications). From this point of view the RG flow changes character at the critical inverse-square coupling, transitioning from a sub-critical regime with evolution between two real, unitary fixed points ( symmetric phase) to a super-critical regime with imaginary, dissipative fixed points ( symmetry broken phase) that represent perfect-sink and perfect-source boundary conditions, around which the flow executes limit-cycle evolution.

Highly efficient achromatic subdiffraction focusing lens in the near field with large numerical aperture

The achromatic subdiffraction lens with large numerical aperture (NA) is of significant importance in optical imaging, photolithography, spectroscopy, and nanophotonics. However, most of the previous research on subdiffraction lenses has been restricted by limited bandwidth and efficiency as well as severe chromatic aberrations. In this paper, a semicircular gradient index lens (sGRIN) with a modified refractive index profile originated from a Maxwell fish-eye lens is put forward to achieve highly efficient (above 81%) achromatic (4–20 GHz) subdiffraction focusing at the focusing line (around 0.28 λ ) with large NA of 1.3 and broadband diffraction-limited far-field radiation (4–16 GHz) theoretically, which overcomes the drawbacks of previous works. The presented lens is designed by gradient dielectric metamaterials. Evanescent waves ignited at the lens/air interface and transformation of electromagnetic (EM) waves with high spatial frequency in sGRIN to EM waves with low spatial frequency in air are responsible for subdiffraction focusing and diffraction-limited far-field radiation, respectively. Experimental results demonstrate the excellent performance of achromatic subdiffraction focusing and diffraction-limited far-field radiation. The presented lens has great potential to be applied in subdiffraction imaging systems.

Evaluation of Deep Learning-Based Neural Network Methods for Cloud Detection and Segmentation

This paper presents a systematic approach for accurate short-time cloud coverage prediction based on a machine learning (ML) approach. Based on a newly built omnidirectional ground-based sky camera system, local training and evaluation data sets were created. These were used to train several state-of-the-art deep neural networks for object detection and segmentation. For this purpose, the camera-generated a full hemispherical image every 30 min over two months in daylight conditions with a fish-eye lens. From this data set, a subset of images was selected for training and evaluation according to various criteria. Deep neural networks, based on the two-stage R-CNN architecture, were trained and compared with a U-net segmentation approach implemented by CloudSegNet. All chosen deep networks were then evaluated and compared according to the local situation.

Generalization of ray tracing in symmetric gradient-index media by Fermat's ray invariants.

Ray tracing in gradient-index (GRIN) media has been traditionally performed either by using the analytical or numerical solutions to the Eikonal equation or by creating a layered medium where Snell's law is calculated in each layer. In this paper, an exact general method to perform ray tracing in GRIN media is presented based on the invariants of the system as stated by Fermat's principle when the media presents symmetries. Its advantage, compared with other methods reported in the literature, relies on its easy implementation. Besides the GRIN distribution and the initial conditions of the incident ray, once the invariants of the system are stated the resulting math is simple to solve and interpret. To benchmark the algorithm, ray tracing in typical cases of GRIN media is calculated, finding minimal discrepancies between the analytical solutions and our simulations. The used media are axial refractive index and parabolic index fiber and lenses with spherical gradient-index symmetry, such as: Luneburg's, Gutman's, generalized Maxwell's Fish-eye, Eaton's, and concentrator lenses. Our method can be further applied to distributions with symmetries associated with other common curvilinear orthogonal coordinate systems, in particular to those associated to the separability of the Helmholtz equation that would allow us to investigate wave optics in these GRIN media with the associated geometries.

Planospheric camera model

Realtime stereo processing, particularly in computationally constrained environments such as the Mars 2020 Perseverance rover, requires image rectification to enable efficient one-dimensional correlation. A camera model has been designed to perform better image rectification for fish-eye lenses with a particular emphasis on the engineering cameras on Perseverance. The primary innovation is the use of a unit projection sphere rather than an image plane as the rectifying surface. For stereo rectification, the rows (for a horizontal pair) or the columns (for a vertical pair) of both cameras must lie on the same epipolar plane. Thus, we use a pair of moving planes to define the rows and columns. Each plane rotates about a dedicated static axis passing through the sphere center. Virtual pixels are located where the planes intersect with each other and the unit sphere.

Stitching Videos from a Fisheye Lens Camera and a Wide-Angle Lens Camera for Telepresence Robots

Many telepresence robots are equipped with a forward-facing camera for video communication and a downward-facing camera for navigation. In this paper, we propose to stitch videos from the FF-camera with a wide-angle lens and the DF-camera with a fisheye lens for telepresence robots. We aim at providing a compact and efficient user interface for telepresence robots with user-friendly interactive experiences. To this end, we present a multi-homography-based video stitching method which stitches videos from a wide-angle camera and a fisheye camera. The method consists of video image alignment, seam cutting, and image blending. We directly align the wide-angle video image and the fisheye video image based on the multi-homography alignment without calibration, distortion correction, and unwarping procedures. Thus, we can obtain a stitched video with shape preservation in the non-overlapping regions and alignment in the overlapping area for telepresence. To alleviate ghosting effects caused by moving objects and/or moving cameras during telepresence robot driving, an optimal seam is found for aligned video composition, and the optimal seam will be updated in subsequent frames, considering spatial and temporal coherence. The final stitched video is created by image blending based on the optimal seam. We conducted a user study to demonstrate the effectiveness of our method and the superiority of user interfaces with a stitched video.

Estimating canopy fuel load with hemispherical photographs: A rapid method for opportunistic fuel documentation with smartphones

Abstract Canopy fuel load (CFL) affects wildfire intensity and is a critical input for fire behaviour models; however, measuring CFL in the field is time‐consuming and costly. Until recently, hemispherical photographs have been unable to adequately describe canopy metrics in non‐diffuse light conditions. Recent developments allow calculation of canopy openness (CO) and leaf area index (LAI) using hemispherical photographs taken in sunny conditions. We describe an inexpensive and effective method for estimating CFL in the field opportunistically using CO and LAI values derived from hemispherical photographs taken in variable lighting conditions with a smartphone and fisheye lens attachment. Implications of this work include: new data for modelling effects of forest structure on fire behaviour; inexpensive assessment and monitoring of forest structure changes over time and in relation to management actions; and decision support for fuel treatment planning and prescribed burning operations.

Dielectric slot-coupled half-Maxwell fisheye lens as octave-bandwidth beam expander for terahertz-range applications

We present a paradigm for integrated photonic devices based on broadband slab-confined collimated beams that are launched with half-Maxwell fisheye lenses. Although it is challenging to match to the low-index focus of the lens while maintaining adequate field confinement for a close approximation of a point source, integrated dielectric slot waveguides prove highly suitable, yielding collimators of 90% efficiency and bandwidth greater than one octave. Terahertz technology will benefit from such broadband slab-confined beams to replace free-space optics toward compact, mass-producible systems that do not require manual optical alignment. We present two prototype systems to demonstrate the versatility of this concept, namely, a diagonally set distributed Bragg reflector as a frequency-division diplexer for terahertz communications and an attenuated total reflection-based liquid sensor. Both are enabled by oblique in-slab reflections that are collected at a location other than the originating lens, which is not attainable using ordinary single-mode channel waveguides.

Study on Distortion Compensation of Underwater Archaeological Images Acquired through a Fisheye Lens and Practical Suggestions for Underwater Photography - A Case of Taean Mado Shipwreck No. 1 and No. 2 -

Underwater archaeology relies heavily on photography and video image recording during surveillances and excavations like ordinary archaeological studies on land. All underwater images suffer poor image quality and distortions due to poor visibility, low contrast and blur, caused by differences in refractive indices of water and air, properties of selected lenses and shapes of viewports. In the Yellow Sea (between mainland China and the Korean peninsula), the visibility underwater is far less than 1 m, typically in the range of 30 cm to 50 cm, on even a clear day, due to very high turbidity. For photographing 1 m x 1 m grids underwater, a very wide view angle (180o) fisheye lens with an 8 mm focal length is intentionally used despite unwanted severe barrel-shaped image distortion, even with a dome port camera housing. It is very difficult to map wide underwater archaeological excavation sites by combining severely distorted images. Development of practical compensation methods for distorted underwater images acquired through the fisheye lens is strongly desired. In this study, the source of image distortion in underwater photography is investigated. We have identified the source of image distortion as the mismatching, in optical axis and focal points, between dome port housing and fisheye lens. A practical image distortion compensation method, using customized image processing software, was explored and verified using archived underwater excavation images for effectiveness in underwater archaeological applications. To minimize unusable area due to severe distortion after distortion compensation, practical underwater photography guidelines are suggested.

Points-connecting neural network ray tracing.

Unsupervised neural network ray tracing (NNRT) to calculate a light ray path connecting given points in a gradient-index medium is proposed here. If two points are given, the NNRT can provide a light ray path passing through these points without knowledge of the light ray direction. Maxwell's fisheye lens having a spherical gradient-index is used to demonstrate how well the NNRT works. Light rays calculated using the NNRT are shown to trace an ideal path passing through given points.

Analysis of Optimal Location for Campus Solar-powered Electric Vehicle Parking Lots Using a Fisheye Lens Camera

Analysis of Optimal Location for Campus Solar-powered Electric Vehicle Parking Lots Using a Fisheye Lens Camera

Partial Maxwell fish-eye lens inspired by the Gutman lens and Eaton lens for wide-angle beam scanning.

This paper presents a novel two-dimensional (2-D) partial Maxwell fish-eye (PMFE) lens with the capability of wide-angle beam scanning inspired by the Gutman lens and Eaton lens, which is obtained by cutting a part from the 2-D Maxwell fish-eye (MFE) lens along a straight line. In terms of the refractive index profile, the MFE lens is similar to the Gutman lens near the center and the Eaton lens near the edge, respectively. We demonstrate the potential of the PMFE lens in wide-angle beam scanning based on its Gutman-like focusing and Eaton-like rotating characteristics corresponding to different feed points. As an example, a fully metallic PMFE lens antenna in the Ka-band composed of a bed of nails and a series of linearly arranged waveguide feeders is designed and experimentally verified. The measured results reveal wide-angle scanning ranges, especially about ±90° at 36 GHz, low reflections and low mutual couplings. The frequency scanning due to the dispersion of the lens is also discussed.

Forest Structure and Composition under Contrasting Precipitation Regimes in the High Mountains, Western Nepal

The high mountains stretch over 20.4% of Nepal’s land surface with diverse climatic conditions and associated vegetation types. An understanding of tree species and forest structural pattern variations across different climatic regions is crucial for mountain ecology. This study strived to carry out a comparative evaluation of species diversity, main stand variables, and canopy cover of forests with contrasting precipitation conditions in the Annapurna range. Firstly, climate data provided by CHELSA version 1.2, were used to identify distinct precipitation regimes. Lamjung and Mustang were selected as two contrasting precipitation regions, and have average annual precipitation of 2965 mm and 723 mm, respectively. Stratified random sampling was used to study 16 plots, each measuring 500 m2 and near the tree line at an elevation range of 3000 to 4000 m across different precipitation conditions. In total, 870 trees were identified and measured. Five hemispherical photos using a fisheye lens were taken in each plot for recording and analyzing canopy cover. Margalef’s index was used to measure species richness, while two diversity indices: the Shannon–Wiener Index and Simpson Index were used for species diversity. Dominant tree species in both study regions were identified through the Important Value Index (IVI). The Wilcoxon rank-sum test was employed to determine the differences in forest structure and composition variables between the two precipitation regimes. In total, 13 species were recorded with broadleaved species predominating in the high precipitation region and coniferous species in the low precipitation region. Higher species richness and species diversity were recorded in the low precipitation region, whereas the main stand variables: basal area and stem density were found to be higher in the high precipitation region. Overall, an inverse J-shaped diameter distribution was found in both precipitation regions signifying uneven-aged forest. A higher proportion of leaning and buttressed trees were recorded in the high precipitation region. However, similar forest canopy cover conditions (>90%) were observed in both study regions. The findings of this research provide a comprehensive narrative of tree species and forest structure across distinct precipitation regimes, which can be crucial to administrators and local people for the sustainable management of resources in this complex region.

A Fast Correction Algorithm for Inverse Longitude and Latitude Mapping of Fish Eye Image

In order to solve the problem of large barrel distortion in fisheye lens, an image distortion correction algorithm based on double longitude is proposed to improve the visual effect. Firstly, in the case of unknown lens angle and non-circular fisheye image, the spherical center and its radius are obtained by using fisheye image features, and the radius is optimized to reduce pole distortion; on this basis, the fisheye image is mapped to the spherical surface by orthogonal projection strategy using double longitude model method, which is transformed into the transverse longitude and longitudinal longitude coordinates of the sphere The projection is a square plane image based on the horizontal and vertical double longitude coordinates to realize the fast and accurate image transformation.

Comparison of cutaneous facial temperature using infrared thermography to standard temperature measurement in the critical care setting.

To assess the accuracy and precision of infrared cameras compared to traditional measures of temperature measurement in a temperature, humidity, and distance controlled intensive care unit (ICU) population. This was a prospective, observational methods comparison study in a single centre ICU in Metropolitan Melbourne, Australia. A convenience sample of 39 patients admitted to a single room equipped with two ceiling mounted thermal imaging cameras was assessed, comparing measured cutaneous facial temperature via thermal camera to clinical temperature standards. Uncorrected correlation of camera measurement to clinical standard in all cases was poor, with the maximum reported correlation 0.24 (Wide-angle Lens to Bladder temperature). Using the wide-angle lens, mean differences were − 11.1 °C (LoA − 14.68 to − 7.51), − 11.1 °C ( − 14.3 to − 7.9), and − 11.2 °C ( − 15.23 to − 7.19) for axillary, bladder, and oral comparisons respectively (Fig. 1a). With respect to the narrow-angle lens compared to the axillary, bladder and oral temperatures, mean differences were − 7.6 °C ( − 11.2 to − 4.0), − 7.5 °C ( − 12.1 to − 2.9), and − 7.9 °C ( − 11.6 to − 4.2) respectively. AUCs for the wide-angle lens and narrow-angle lens ranged from 0.53 to 0.70 and 0.59 to 0.79 respectively, with axillary temperature demonstrating the greatest values. Infrared thermography is a poor predictor of patient temperature as measured by existing clinical standards. It has a moderate ability to discriminate fever. It is unclear if this would be sensitive enough for infection screening purposes.Fig. 1Bland–Altman plots for temperatures measured using clinical standards to infrared camera. a Wide-angle camera versus bladder temperature. b Narrow-angle camera versus bladder temperatureSupplementary InformationThe online version contains supplementary material available at 10.1007/s10877-021-00731-y.

Modernism Edited: Marianne Moore and the Dial Magazine

<i>Modernism Edited: Marianne Moore and the</i> Dial <i>Magazine</i>

Eye lenses reveal ontogenetic trophic and habitat shifts in an imperiled fish, Clear Lake hitch (Lavinia exilicauda chi)

Stable isotopes recorded in fish eye lenses are an emerging tool to track dietary shifts coincident with use of diverse habitats over the lifetime of individuals. Eye lenses are metabolically inert, sequentially deposited, archival tissues that can open avenues to chronicle contaminant exposures, diet histories, trophic dynamics and migratory histories of individual fishes. In this study, we demonstrated that trophic histories reconstructed using eye lenses can resolve key uncertainties regarding diet and trophic habitat shifts. Clear Lake hitch (Lavinia exilicauda chi), a threatened cyprinid, inhabits a single lake (Clear Lake, Lake County, California) and utilizes tributary streams for reproduction. Bayesian mixing models applied to δ13C and δ15N recorded in eye lenses uncovered ontogenetic diet shifts that corresponded with shifts in occupation of habitats providing spawning (tributary streams), rearing (littoral lake), and growth (pelagic lake) functions. The reconstruction of size-structured trophic and habitat information can provide vital information needed to manage and conserve imperiled species such as the Clear Lake hitch.

Effects of chronic physical activity on cognition across the lifespan: a systematic meta-review of randomized controlled trials and realist synthesis of contextualized mechanisms

ABSTRACT In the surging field of chronic physical activity (PA) and cognition research, problems arise that prevent us from ‘seeing the forest for the trees’. The first aim was to identify them and propose solutions. Moreover, inconsistencies in conclusions of a rising amount of systematic reviews render necessary ‘an umbrella for a rain of evidence’. The second aim was to obtain a differentiated picture of moderators that may explain inconsistencies using the wide-angle lens of a systematic meta-review. We especially addressed the role of the PA context in causation mechanisms, complementing the meta-review with a realist approach that is best suited to identify context-mechanism-outcome (CMO) configurations. Main review outcomes are: (1) inconsistent grading of methodological quality and low consideration of external validity; (2) role of multiple moderators at participant-, intervention-, study-level but relative neglect of context-level moderators; (3) explanatory potential of CMO configurations, in which specific conditions of the context may trigger different mechanisms that generate PA effects on cognition. The majority of the proposed mechanisms converge on the concept of enrichment. Conclusions highlight the need for future research, in which PA interventions and their contexts are designed to mobilize the different mechanisms underpinning their individual and joint effects on cognition.

Perforated extensible 3-D hyperbolic secant lens antenna for directive antenna applications using additive manufacturing.

In this paper, a novel three-dimensional (3-D) generalized hyperbolic secant (H-S) lens is first introduced using perforated dielectric material. The attractiveness of this new lens is its unique intrinsic flat shape characteristic and extensibility for different configuration scenarios, which provide a potential alternative design for a planar Luneburg and half Maxwell fish-eye lens based on a complex conformal mapping method. A high gain and wideband printed antipodal fermi antenna as a feeding source is employed in the proposed lens antenna prototype. The high radiation performance with low side lobe level of the fabricated lens prototype is validated from 8.2GHz to 12.5GHz, demonstrating 23.8 dBi realized gain at 10 GHz with 3-dB beamwidth of 9° and 2-dB fractional gain bandwidth of 41.6%. Besides, the total radiation efficiency is above ∼40% across all tested frequencies, which suggests the proposed H-S lens itself has a broadband response. The simplicity and low-cost fabrication using additive manufacturing of its lens design indicates great potential in broadband high directive antenna applications.