Nearby Light Sources Research Articles

Remote Blood Oxygen Estimation From Videos Using Neural Networks.

Peripheral blood oxygen saturation (SpO 2) is an essential indicator of respiratory functionality and received increasing attention during the COVID-19 pandemic. Clinical findings show that COVID-19 patients can have significantly low SpO 2 before any obvious symptoms. Measuring an individual's SpO 2 without having to come into contact with the person can lower the risk of cross contamination and blood circulation problems. The prevalence of smartphones has motivated researchers to investigate methods for monitoring SpO 2 using smartphone cameras. Most prior schemes involving smartphones are contact-based: They require using a fingertip to cover the phone's camera and the nearby light source to capture reemitted light from the illuminated tissue. In this paper, we propose the first convolutional neural network based noncontact SpO 2 estimation scheme using smartphone cameras. The scheme analyzes the videos of an individual's hand for physiological sensing, which is convenient and comfortable for users and can protect their privacy and allow for keeping face masks on. We design explainable neural network architectures inspired by the optophysiological models for SpO 2 measurement and demonstrate the explainability by visualizing the weights for channel combination. Our proposed models outperform the state-of-the-art model that is designed for contact-based SpO 2 measurement, showing the potential of the proposed method to contribute to public health. We also analyze the impact of skin type and the side of a hand on SpO 2 estimation performance.

Modeling the artificial night sky brightness at short distances from streetlights

Contrary to some widespread intuitive belief, the night sky brightness perceived by the human eye or any other physical detector does not come (exclusively) from high in the sky. The detected brightness is built up from the scattered radiance contributed by all elementary atmospheric volumes along the line of sight, starting from the very first millimeter from the eye cornea or the entrance aperture of the measuring instrument. In artificially lit environments, nearby light sources may be responsible for a large share of the total perceived sky radiance. We present in this paper a quantitative analytical model for the sky radiance in the vicinity of outdoor light sources, free from singularities at the origin, which provides useful insights for the correct design or urban dark sky places. It is found that the artificial zenith sky brightness produced by a small ground-level source detected by a ground-level observer at short distances (from the typical dimension of the source up to several hundred meters) decays with the inverse of the distance to the source. This amounts to a reduction of 2.5 mag/arcsec2 in sky brightness for every log10 unit increase of the distance. The effects of screening by obstacles are also discussed.

Controlling the artificial radiance of the night sky: The Añora urban laboratory

We provide radiometric evidence of the relevance of nearby light sources on the artificial brightness of the night sky. To obtain the required data we developed a method based on the use of power-regulated urban lighting systems, which also provides relevant information on the propagation of light pollution at short distances from the sources. A controlled experiment was carried out in the Andalusian municipality of Añora (1526 inhab.) in which the radiant power of its regulated public outdoor lighting system was modified in a predefined way during the central part of the night while continuously recording the zenith sky brightness in the TESS-W photometric band from two separate locations inside the town. We determined that the power-regulated streetlight sources contribute a 60–62% to the total zenith sky brightness at these observing locations in clear and moonless nights when operated at their maximum power rating, being the remaining sky radiance due to constant local sources and sources from neighboring towns. These results, in combination with georeferenced information on the sources' location and properties, impose some constraints on the functional form of the effective point-spread functions (PSF) of the zenith sky brightness at short distances from the sources. For the conditions of our experiment we have found that the expected exponents of power-law PSFs are close to -1.

A Multi-Channel Ratio-of-Ratios Method for Noncontact Hand Video Based SpO$_2$ Monitoring Using Smartphone Cameras

Blood oxygen saturation (SpO<inline-formula><tex-math notation="LaTeX">$_2$</tex-math></inline-formula>) is an important indicator forpulmonary and respiratory functionalities. Clinical findings on COVID-19 show that many patients had dangerously low blood oxygen levels not long before conditions worsened. It is therefore recommended, especially for the vulnerable population, to regularly monitor the blood oxygen level for precaution. Recent works have investigated how ubiquitous smartphone cameras can be used to infer SpO<inline-formula><tex-math notation="LaTeX">$_2$</tex-math></inline-formula>. Most of these works are contact-based, requiring users to cover a phone&#x2019;s camera and its nearby light source with a finger to capture reemitted light from the illuminated tissue. Contact-based methods may lead to skin irritation and sanitary concerns, especially during a pandemic. In this paper, we propose a noncontact method for SpO<inline-formula><tex-math notation="LaTeX">$_2$</tex-math></inline-formula> monitoring using hand videos acquired by smartphones. Considering the optical broadband nature of the red (R), green (G), and blue (B) color channels of the smartphone cameras, we exploit all three channels of RGB sensing to distill the SpO<inline-formula><tex-math notation="LaTeX">$_2$</tex-math></inline-formula> information beyond the traditional ratio-of-ratios (RoR) method that uses only two wavelengths. To further facilitate an accurate SpO<inline-formula><tex-math notation="LaTeX">$_2$</tex-math></inline-formula> prediction, we design adaptive narrow bandpass filters based on accurately estimated heart rate to obtain the most cardiac-related AC component for each color channel. Experimental results show that our proposed blood oxygen estimation method can reach a mean absolute error of 1.26&#x0025; when a pulse oximeter is used as a reference, outperforming the traditional RoR method by 25&#x0025;.

Distribution of Triatoma dimidiata sensu lato (Reduviidae: Triatominae) and Risk Factors Associated with Household Invasion in Northern Belize, Central America

To date, Triatoma dimidiata sensu lato [Reduviidae: Triatominae (Latreille 1811)] remains the sole vector species associated with Chagas disease transmission reported from Belize. Human infection data are limited for Belize and the disease transmission dynamics have not been thoroughly investigated, yet the likelihood of autochthonous transmission is supported by the widespread collection of infected vectors from within local households. Here, we report updated infection rates of the vector population and infestation rates for villages in north and central Belize. Overall, 275 households were enrolled in an ongoing vector surveillance program. Of the 41 insects collected, 25 were PCR positive for T. cruzi, indicating an infection rate as high as 60%. To further characterize the epidemiological risk of human–vector contact, determinants of household invasion were modeled. Local households were surveyed and characterized with respect to over 25 key factors that may be associated with household infestation by T. dimidiata s.l. While final models were not strongly predictive with respect to the risk factors that were surveyed, likely due to the low number of collection observations, the presence of domestic/peri-domestic dogs, nearby light sources, and household structure materials could be the focus of continued risk assessments. In northern Belize, this vector survey lends support to T. dimidiata s.l. inhabiting sylvatic settings as opposed to the classical paradigm of domiciliated vector populations. This designation has strong implications for the local level of human exposure risk which can help guide vector surveillance and control resources.

Shape from shading under inconsistent illumination.

People are able to perceive the 3D shape of illuminated surfaces using image shading cues. Theories about how we accomplish this often assume that the human visual system estimates a single lighting direction and interprets shading cues in accord with that estimate. In natural scenes, however, lighting can be much more complex than this, with multiple nearby light sources. Here we show that the human visual system can successfully judge 3D surface shape even when the lighting direction varies from place to place over a surface, provided the scale at which these lighting changes occur is similar to, or larger than, the size of the shape features being judged. Furthermore, we show that despite being able to accommodate rapid changes in lighting direction when judging shape, observers are generally unable to detect these changes. We conclude that, rather than relying on a single estimated illumination direction, the human visual system can accommodate illumination that varies substantially and rapidly across a surface.

COSMOLOGICAL SIMULATIONS OF EARLY BLACK HOLE FORMATION: HALO MERGERS, TIDAL DISRUPTION, AND THE CONDITIONS FOR DIRECT COLLAPSE

ABSTRACT Gravitational collapse of a massive primordial gas cloud is thought to be a promising path for the formation of supermassive black holes in the early universe. We study conditions for the so-called direct collapse (DC) black hole formation in a fully cosmological context. We combine a semianalytic model of early galaxy formation with halo merger trees constructed from dark matter N-body simulations. We locate a total of 68 possible DC sites in a volume of on a side. We then perform hydrodynamics simulations for 42 selected halos to study in detail the evolution of the massive clouds within them. We find only two successful cases where the gas clouds rapidly collapse to form stars. In the other cases, gravitational collapse is prevented by the tidal force exerted by a nearby massive halo, which otherwise should serve as a radiation source necessary for DC. Ram pressure stripping disturbs the cloud approaching the source. In many cases, a DC halo and its nearby light source halo merge before the onset of cloud collapse. When the DC halo is assembled through major mergers, the gas density increases rapidly to trigger gravitational instability. Based on our cosmological simulations, we conclude that the event rate of DC is an order of magnitude smaller than reported in previous studies, although the absolute rate is still poorly constrained. It is necessary to follow the dynamical evolution of a DC cloud and its nearby halo(s) in order to determine the critical radiation flux for DC.

Inpainting for Fringe Projection Profilometry Based on Geometrically Guided Iterative Regularization.

Conventional fringe projection profilometry methods often have difficulty in reconstructing the 3D model of objects when the fringe images have the so-called highlight regions due to strong illumination from nearby light sources. Within a highlight region, the fringe pattern is often overwhelmed by the strong reflected light. Thus, the 3D information of the object, which is originally embedded in the fringe pattern, can no longer be retrieved. In this paper, a novel inpainting algorithm is proposed to restore the fringe images in the presence of highlights. The proposed method first detects the highlight regions based on a Gaussian mixture model. Then, a geometric sketch of the missing fringes is made and used as the initial guess of an iterative regularization procedure for regenerating the missing fringes. The simulation and experimental results show that the proposed algorithm can accurately reconstruct the 3D model of objects even when their fringe images have large highlight regions. It significantly outperforms the traditional approaches in both quantitative and qualitative evaluations.

Color constancy using 3D scene geometry derived from a single image.

The aim of color constancy is to remove the effect of the color of the light source. As color constancy is inherently an ill-posed problem, most of the existing color constancy algorithms are based on specific imaging assumptions (e.g., gray-world and white patch assumption). In this paper, 3D geometry models are used to determine which color constancy method to use for the different geometrical regions (depth/layer) found in images. The aim is to classify images into stages (rough 3D geometry models). According to stage models, images are divided into stage regions using hard and soft segmentation. After that, the best color constancy methods are selected for each geometry depth. To this end, we propose a method to combine color constancy algorithms by investigating the relation between depth, local image statistics, and color constancy. Image statistics are then exploited per depth to select the proper color constancy method. Our approach opens the possibility to estimate multiple illuminations by distinguishing nearby light source from distant illuminations. Experiments on state-of-the-art data sets show that the proposed algorithm outperforms state-of-the-art single color constancy algorithms with an improvement of almost 50% of median angular error. When using a perfect classifier (i.e, all of the test images are correctly classified into stages); the performance of the proposed method achieves an improvement of 52% of the median angular error compared with the best-performing single color constancy algorithm.

Light pollution simulations for planar ground-based light sources

The light pollution model is employed to analyze spatial behavior of luminance at the night sky under cloudless and overcast conditions. Enhanced light excess is particularly identified at cloudy skies, because the clouds efficiently contribute to the downward luminous flux. It is evident that size of ground-based light sources can play an important role in the case of overcast sky conditions. Nevertheless, the realistically sized light sources are rarely embedded into light pollution modeling, and rather they are replaced by simple point sources. We discuss the discrepancies between sky luminance distributions when at first the planar light sources are considered and at second the point-source approximation is accepted. The found differences are noticeable if the size of the light source, distance to the observer, and altitude of a cloudy layer are comparable one to the other. Compared with point-source approximation, an inclusion of the size factor into modeling the light sources leads to partial elimination of the steep changes of sky luminance (typical for point sources of light). The narrow and sharp light pillars normally presented on the sky illuminated by point light sources can disappear or fuse together when two or more nearby light sources are considered with their real sizes. Sky elements situated close to the horizon will glow efficiently if luminous flux originates from two-dimensional ground-based entities (such as cities or villages).

New algorithms generate improved templates for biometric recognition

Face detection and eye gaze estimation are crucial components of applications such as virtual reality, video conferencing, video surveillance, face recognition and face database management.1–4 New applications involving human-machine interfaces are under development where eye gaze could be employed to control machines assisting handicapped individuals, or in technologically complex environments such as hospital operating rooms, airplane cockpits, or industrial control units.1, 5–7 Several limitations have been identified in existing face and iris detection methods: some are invasive; some focus on only one eye, do not follow head movements, or only follow very small head movements; some fail to detect eyes while blinking; and some require manual initialization. Additionally, some impose restrictions such as symmetry, which limits the background content. Other methods depend on face skin tone, which varies among different ethnic groups and is dependent upon nearby light sources. These limitations contribute to two particular problems that apply to most methods of face and eye detection: they cannot work in real time, and they are not robust for face rotations.1, 8–12 To allow real-time processing, our first approach was to use anthropometric templates for face and eye detection. This set of templates, which consists of different face sizes, includes key facial features such as eyebrows, nose, mouth, and the lower part of the chin, thus mainly limiting the search to these specific face and eye characteristics. For eye detection, the templates consider an eye region within an elliptical face contour. Our second approach was to design templates using PSO (particle swarm optimization) to search for the best templates,8 or use a local component maximization (CM) procedure.9 The Figure 1. (a) Coarse face detection: original image, coarse directional image, accumulator, superposition of accumulator over original image, and coarse face detection. (b) Fine face detection: original image, coarse face detection, fine directional image, anthropometric face templates, and face detection by face template.

Improved algorithm for simulations of divergent-light halos

Divergent-light halos are produced when light from nearby light sources is scattered by ice crystals in the atmosphere. We present a theory of divergent-light halos leading to an improved algorithm for the simulation of such halos. Contrary to the algorithm that we presented earlier for simulating such halos, the new algorithm includes a mathematically rigorous weighting of the events. The computer implementation is very compact, and the whole procedure is elegant and conceptually easy to understand. We also present a new simulation atlas showing halos produced by crystals of different shapes and orientations for a set of elevations of the light source.

Simple non-invasive measurement of rapid eye vibration

A simple, non-invasive method for the measurement of eye vibrations above 30 Hz is described. The method can be used in either laboratory or natural conditions, and is based on the cancellation of an illusion of motion that occurs when two nearby light sources flickering in counterphase above the flicker fusion limit are observed during eye vibration. In these conditions, the light sources appear to oscillate in space at a frequency equal to the difference between the vibration and flicker frequencies. The frequency of eye vibration can be determined by adjusting the flicker frequency until the illusion disappears (i.e., until the difference frequency becomes zero). The same set-up can also be used to determine the amplitude of eye vibration, by adjusting the spatial separation between the two light sources until the oscillation appears to be the result of their bouncing off each other upon contact. The reliability and sensitivity of this method are illustrated with data from three observers whose eyes were vibrated with a commercial massager applied onto their neck, and using three different settings for the speed of the massager.

Procedure for simulating divergent-light halos.

Divergent-light halos are halos produced by light from nearby light sources, like street lamps being scattered by small crystals of ice floating in the air. The use of "brute-force" Monte Carlo methods to simulate such halos is extremely inefficient, as most scattered rays will not hit the eye of the observer. I present a new procedure for Monte Carlo simulations of divergent-light halos. This procedure uses rotational symmetries to make a selected sampling of events that greatly improves the computational efficiency of the algorithm. We can typically generate a simulated halo display in minutes using a personal computer, several orders of magnitude more rapid than a simple brute-force method. The algorithm can also optionally generate three-dimensional pictures of divergent-light halo displays.

Comparison of Sun pillars with light pillars from nearby light sources

Using a Monte Carlo method, we simulate the appearance of light pillars produced by nearby light sources and compare their appearance with simulations of Sun pillars. Photographs of light pillars are also compared with the simulations. We expand the idea of light and Sun pillars by examining the reflected-light patterns from several different known distributions of airborne ice crystals. Polarization properties of light pillars from nearly horizontally oriented plate crystals are also simulated.

Polarization and Brewster angle properties of light pillars

Numerical simulation of the nocturnal light pillar, an atmospheric optical phenomenon inadvertently caused by humans, reveals that the pillars are virtually completely polarized at the Brewster angle for ice as a result of the geometry of rays reflected off near-horizontally aligned ice crystals from a nearby light source. It is also shown for plate crystals that the first-order internal reflection contributes importantly to the display and that the depth of the crystal-containing layer and the effects of atmospheric attenuation serve to limit the height above the horizon to which the pillars are visible. The model findings have been verified with experiments involving the generation of artificial pillars from linearly polarized light sources. Both observations and model predictions support the view that the plate ice crystals causing the display have tilt angles that are distributed normally from the horizontal plane.

STUDIES ON THE BEHAVIOR OFNASSARIUS OBSOLETUS(SAY) (MOLLUSCA, GASTROPODA)

The reactions of specimens of Nassarius obsoletus exposed individually to controlled laboratory stimuli are as follows:1. Nassarius shows a light-compass reaction, but no optomotor response.2. On damp slopes Nassarius moves downhill. Submerged Nassarius is generally geonegative but its response is altered by a nearby light source.3. In clean seawater Nassarius moves downstream.4. Addition of effluents from damaged animal tissues or from mud causes a reversal of rheotaxis.5. A small but significant upstreaming response is elicited by water of raised oxygen concentration.6. The upstreaming response to olfactory stimuli can be abolished when unfavorable stimuli (hypo-or hypersalinity) are simultaneously present.7. Water which has passed over living, intact Nassarius is attractive to other individuals of the species Nassarius, the attraction not being due to faeces.8. When simultaneously presented with substrates of different kinds, mud snails accumulate on those richest in diatoms and bacteria.9. The behavior of an individual Nassarius is greatly affected by the behavior of others around it. Members of a group of Nassarius in the laboratory or in the field show a strong tendency to conform in their direction of movement, thus producing schooling. The orientation of schools in the field was that expected from the behavior of the majority of individuals in the laboratory.