Background Illumination Level Research Articles

Analyzing the effect of shot noise in indirect Time-of-Flight cameras

Continuous wave indirect Time-of-Flight cameras obtain depth images by emitting a modulated continuous light wave and measuring the delay of the received signal. In this paper we generalize the estimation of the effect of the shot noise when obtaining the phase delay with an arbitrary number of points in the Discrete Fourier Transform, extending and generalizing the analysis done in previous works for the case of four points. For that particular case, we compare our analysis with the state of art. Moreover, we extend the error model using a second order approximation in the error propagation analysis, which provides more accurate estimations according to the Montecarlo simulation experiments. The analysis, based on both analytical and numerical methods, shows that the phase error is, in general, related to the exposure time and weakly to the number of points in the Discrete Fourier Transform. It also depends on the background illumination level, on the amplitude of the received signal, and, when using a three point DFT, on the distance to the objects.

The Bovine Ex Vivo Retina: A Versatile Model for Retinal Neuroscience.

The isolated ex vivo retina is the standard model in retinal physiology and neuroscience. During isolation, the retina is peeled from the retinal pigment epithelium (RPE), which plays a key role in the visual cycle. Here we introduce the choroid-attached bovine retina as an in vivo-like model for retinal physiology. We find that-in the bovine eye-the choroid and retina can be peeled from the sclera as a single thin sheet. Importantly, the retina remains tightly associated with the RPE, which is sandwiched between the retina and the choroid. Furthermore, bovine tissue is readily available and cheap, and there are no ethical concerns related to the use of animals solely for research purposes. We combine multi-electrode array and single-cell patch-clamp recordings to characterize light responses in the choroid-attached bovine ex vivo retina. We demonstrate robust and consistent light responses in choroid-attached preparations. Importantly, light responses adapt to different levels of background illumination and rapidly recover from photobleaching. The choroid-attached retina is also thin enough to permit targeted electrophysiological recording from individual retinal neurons using standard differential interference contrast microscopy. We also characterize light responses and membrane properties of bovine retinal ganglion cells and compare data obtained from bovine and murine retinas. The choroid-attached retinal model retains the advantages of the isolated retina but with an intact visual cycle and represents a useful tool to elucidate retinal physiology.

A high performance integrated readout circuit for wavefront sensors

This work presents an integrated pixel topology that promises to offer superior performance in a Hartmann–Shack Wavefront Sensor (WFS) with an orthogonal array of Quad Cells serving as Position-Sensitive Detectors. The readout integrated circuit for each photodiode is fully compliant to any standard CMOS microelectronics technology and is advantageously tolerant to high background illumination levels whereas maintaining both high linearity and high sensitivity. To assess the operation of this pixel on the focal-plane array of the WFS, we developed a computational platform encompassing a full detection chain comprising wavefront sampling, photodetection, electronic circuitry and wavefront reconstruction. It couples an algorithm written in C to SPICE (Simulated Program with Integrated Circuits Emphasis). The platform is technology agnostic and flexible, enabling easy modification to represent different detection or reconstruction methods. The results obtained with the proposed pixel have been compared to those obtained with a conventional pixel in CMOS image sensor.

Energy-Efficient Image Recognition System for Marine Life

This article focuses on designing an energy-efficient image recognition system for marine monitoring. One of the main challenges of an underwater imaging system is the strict power consumption constraints due to the limited on-site resources. Considering the need for continuous operation in different water turbidity levels and background illumination conditions, an energy-efficient approach is needed for the effective utilization of the resources. In this work, we propose a recognition framework that will adaptively adjust the system parameters, such as camera frame rate and LED illumination level, based on the environmental conditions to optimize the energy consumption while ensuring a high recognition accuracy. The first part of the proposed decision system contains the convolutional neural network (CNN)-based animal recognition block which is used for obtaining the confidence level for a single frame. The second part is the adaptive decision block that dynamically changes the system parameters and combines the results of the recognition block for multiple frames based on the environmental conditions. In our experiments, we have used nearly 8000 underwater images for training and testing the single frame recognition block and used nearly 200 different video sequences for training and testing the adaptive decision block. Based on measurements of a hardware framework composed of a Raspberry Pi 3 Model B, a Pi NoIR Camera v2.1, and 850 nm LEDs, the proposed system achieves up to 92.7% energy savings with a comparable recognition performance by dynamically changing the frame rate and emitted light intensity based on water turbidity and background illumination level.

The Photomotor Response - Dynamic Quantification by a Portable Pupillometer

The pupillary light reflex (PLR) is a key component of the physical examination as it reliably tests the functional integrity of the neuromuscular loop between pupil and midbrain. Unlike the traditional manual testing the PLR with a penlight that frequently leads to incorrect interpretation due to its subjectivity, the specialized “pupillometer” tool allows objective testing and trending of pupillary data. We performed quantitative unilateral pupillometry several times in 53 healthy subjects (aged 21-74) in different background illumination levels using the NeurOptics NPi®-200 pupillometer. A number of key parameters describing the PLR were collected and analysed. We found that the individual PLR was very consistent. In general, constriction velocity (the first part of the PLR when the pupil constricts promptly after the onset of a light stimulus) was brisker than the dilation velocity (the second part of the PLR, when the pupil recovers from the constriction). Most importantly, both velocities depend on the initial pupillary resting size. We proved that pupillary parameters depend on environmental light conditions and age, but not gender, and scrutinized the nature and dynamics of anisocoric pupils. Taking together, pupillometry is becoming an important, non-invasive clinical tool for testing the autonomic nervous system. Here, we describe baseline parameters representing the physiological PLR, confirming and extending previously reported data. We thus provide the clinician important criteria to precisely assess the PLR and hence the autonomic nervous system in different pathological conditions such as diabetes, traumatic brain injury or cardiac and other autonomic neuropathies.

A System for Registering Shadow Images of Rapid Processes in the UV Spectral Range under the Conditions of Intense Background Illumination

A system is presented for registering shadow images obtained from dense pulsed plasma with a high background illumination level, wherein an LGI-21 molecular nitrogen laser is used as an illuminator (laser pulse power 12 µW, duration 20 ns), and a modified Canon EOS 1000D camera is used as a registering unit. A micropinch discharge such as a high-current low-inductance vacuum spark (HCLIVS) has been used as the plasma object under investigation.

Mid-wavelength infrared InAsSb/InAs nBn detectors and FPAs with very low dark current density

There was a significant improvement in the performance of infrared nBn detectors utilizing InAs/InAsSb absorbers culminating in the development of infrared focal plane arrays (FPAs) with excellent operability (99.7%) and operating at temperature significantly higher than InSb FPAs. In this work, we demonstrated that these detectors can operate with very low dark current densities enabling their use in applications with a low-to-medium level of background illumination. We showed that single pixel photodetectors with a cut-off wavelength of 4.8 μm and a quantum efficiency of QEmax = 35% under backside-illumination have a dark current density of 1 × 10−10 A/cm2 at an operating bias of −0.1 V and temperature T = 100 K. Additionally, we compared the single pixel dark current results with measurements of the dark current in FPAs. The FPA showed excellent performance with an operability of 99.7% and was able to reach a mode dark current density of 5 × 10−11 A/cm2 at 80 K.

The light-dark task in zebrafish confuses two distinct factors: Interaction between background shade and illumination level preference

The light-dark preference task has been commonly used in rodents to screen for anxiogenic and anxiolytic drugs. However, recent adaptations of the light-dark preference test for zebrafish have produced inconsistent results. Several studies have reported that zebrafish exhibit a preference for light, while others have found a preference for black. We suggest the inconsistencies may be the result of confusing certain parameters of the test leading to improper interpretation. For example, researchers often use “light” interchangeably with “white” and “dark” with “black” when these are two distinct factors: level of illumination vs. background shade. In the current study, we use specifically designed preference tanks to investigate the influence of background shade (i.e. white vs. black) and level of illumination (i.e. light vs. dark) on preference and anxiety-like behaviour. Furthermore, we pharmacologically validate our results by quantifying the effects of ethanol, a drug with known anxiety-altering properties, on anxiety-like behaviours. Here we report that zebrafish's preference varies depending upon background shade and level of illumination. We also found that ethanol administration altered behavioural responses in an illumination- and background shade-dependent manner. Our findings reinforce the need to correctly differentiate between these factors when interpreting results obtained with this behavioural paradigm. Lastly, our results show that simple modifications to the experimental tank in which anxiety-related responses are measured can significantly alter behaviour of zebrafish, supporting the need for standardized testing procedures and/or for detailed description of experimental procedures and the apparatus.

Gamma-ray observations under bright moonlight with VERITAS

Imaging atmospheric Cherenkov telescopes (IACTs) are equipped with sensitive photomultiplier tube (PMT) cameras. Exposure to high levels of background illumination degrades the efficiency of and potentially destroys these photo-detectors over time, so IACTs cannot be operated in the same configuration in the presence of bright moonlight as under dark skies. Since September 2012, observations have been carried out with the VERITAS IACTs under bright moonlight (defined as about three times the night-sky-background (NSB) of a dark extragalactic field, typically occurring when Moon illumination > 35%) in two observing modes, firstly by reducing the voltage applied to the PMTs and, secondly, with the addition of ultra-violet (UV) bandpass filters to the cameras. This has allowed observations at up to about 30 times previous NSB levels (around 80% Moon illumination), resulting in 30% more observing time between the two modes over the course of a year. These additional observations have already allowed for the detection of a flare from the 1ES 1727 + 502 and for an observing program targeting a measurement of the cosmic-ray positron fraction. We provide details of these new observing modes and their performance relative to the standard VERITAS observations.

A Brand New World: Impacts Study of the Background Luminance and Illumination Level on Measuring of LED Billboards in Taiwan

A Brand New World: Impacts Study of the Background Luminance and Illumination Level on Measuring of LED Billboards in Taiwan

Low levels of light pollution may block the ability of male glow-worms (Lampyris noctiluca L.) to locate females

Light pollution has been proposed as a factor in the decline of Lampyris noctiluca because it has the potential to interfere with reproductive signaling and has been shown to impact the ability of males to locate light lures in a suburban environment. To compare and test the replicability of this effect in a natural setting and population, imitation females were set out under light polluted and control conditions at varying light pollution intensities in an undisturbed British chalk grassland. Very low levels of light pollution were found to interfere with phototaxis: no males were attracted at either 0.3 or 0.18 lux background lighting versus 33 males collected at paired dark controls. These background illumination levels are much lower than that of 1.5 lux which is recommended by local city councils in Britain to light footpaths. A survey of female L. noctiluca numbers and distribution showed a trend towards female clumping that was not statistically significant. We also found no evidence of light interfering with female signaling behavior.

The effect of age‐related lens yellowing on Farnsworth–Munsell 100 hue error score

To investigate the effects of real and simulated age-related changes in crystalline lens yellowing on Farnsworth-Munsell (FM) 100 hue performance. FM 100 hue total and partial error scores (PES) were measured in a group of younger (n=10, mean age=22.2+/-2.65 years) and a group of older (n=10, mean age=54.5+/-2.64 years) normal observers along with psychophysical estimates of crystalline lens optical density and pupil size. Three younger observers underwent repeated FM 100 hue testing under a variety of simulated age-related lens yellowing conditions, using filters with well-defined transmittance properties which attempted to mimic the real age-related lens yellowing changes of the older group. FM 100 hue total and PES were significantly higher in the older age group compared with the younger group (p<0.01). Lens density measures were significantly higher in the older age group compared with the young group (p<0.01), but showed less scatter than individual FM 100 hue error scores. Simulated lens yellowing in the three younger observers, equivalent to the level of that of the older observers, did not affect any of their FM 100 hue total or PES. Simulation of age-related lens yellowing in younger observers has little effect on FM 100 hue error score. A variety of other factors such as pupil size, background illumination level, iris colour and macular pigment density may contribute to the age-related increase in FM 100 hue scores.

Standoff determination of the particle size and concentration of small optical depth clouds based on double-scattering measurements: validation with calibrated target plates and limitations for daytime and nighttime measurements

Diffractive target plates are used to emulate aerosols of known size and concentration. These target plates are used to validate and determine the sensitivity of a multiple-field-of-view lidar signal inversion technique based on double-scattering measurement to retrieve the particle size and the concentration of small optical depth clouds. We estimate that nighttime and daytime quantification (size and concentration) is possible for optical depths as low as 0.005 and 0.016, respectively. The recovery technique limiting factors are the shot noise, the laser features, the optical lens quality, the background illumination level, the background aerosol fluctuations, and the noise introduced by the lidar detector, a gated intensified camera (camera G-ICCD).

Rod and Cone Contributions to Horizontal Cell Light Responses in the Mouse Retina

Mammalian B-type horizontal cells make contact with both photoreceptor types: the dendrites contact cone photoreceptors, whereas the axon terminal processes contact rods. Despite their distinct synaptic contacts, horizontal cell somata and axon terminals receive a mixture of rod and cone inputs. Interaction of the two photoreceptor systems is essential for adaptation of photoreceptor sensitivity to different levels of background illumination, and horizontal cells play a key role in this adaptation. In this study, we used transgenic mouse lines to examine the contributions of rod and cone photoreceptor inputs to horizontal cell light responses in the mouse retina: rod signals were isolated by recording intracellularly from horizontal cells in a mouse lacking the cone cyclic nucleotide-gated channel, which lacks cone function, and cone signals were assessed using the rhodopsin knock-out mouse, which is a model for pure cone function. We found that both horizontal cell compartments receive a mixture of inputs from both photoreceptor types. To determine whether these inputs arrive via the long axon connecting the compartments or by way of rod-cone gap junctional coupling, we assessed the rod and cone contributions to horizontal cell somatic and axon terminal light responses in the connexin36-deficient mouse retina, which lacks rod-cone coupling. Our results confirm that rods and cones are coupled by connexin36, and suggest that signal transmission along the axon is unidirectional: signals are passed from horizontal cell soma to axon terminal but not from axon terminal to soma.

Age‐related lens yellowing per se contributes little to the increase in Farnsworth‐Munsell 100 hue error scores with age

Purpose: To investigate the effects of real and simulated age‐related changes in crystalline lens yellowing on Farnsworth–Munsell (FM) 100 hue total and partial error scores.Methods: FM 100 hue total and partial error scores were measured in a group of younger (n = 10, mean age 22.2 ± 2.65 years) and a group of older (n = 10, mean age = 54.5 ± 2.64 years) normal observers along with psychophysical estimates of crystalline lens optical density and pupil size measurements. Three younger observers underwent repeated FM 100 hue testing using a variety of simulated age‐related lens yellowing conditions, using filters with well‐defined absorption properties which mimicked the real age‐related lens yellowing changes of the older group. FM 100 hue scores were also measured under different levels of background illumination and pupil size in the 3 younger observers.Results: FM 100 hue total and partial error scores were significantly higher in the older age group compared to the younger group (p &lt;0.01). Lens density measures were significantly higher in the older age group compared to the young group (p&lt;0.01), but showed less scatter with age than FM 100 hue error scores. Pupil size was significantly larger in the younger group compared to the older group (p&lt;0.01). Simulated lens yellowing in the three younger observers, equivalent to the level of that of the older observers, did not affect any of their FM 100 hue total or partial error scores. Reductions in pupil size and illumination significantly affected the younger observers’ performance, with increases in error score equivalent to the observed age‐related decline between the younger and older group.Conclusions: Lens yellowing per se makes little contribution to the increase in Farnsworth–Munsell 100 hue error score with increasing age. Retinal illumination levels and pupil size can significantly affect the error score and should be considered when interpreting FM 100 hue error scores in older subjects. Clinicians should also consider iris colour and macular pigment density when interpreting FM 100 hue error scores.

Separate effects of background and illumination on lightness

Four experiments attempted to establish an effect of context on lightness. Lightness is one of the dimensions of color and it varies from black to white. Most of our stimuli were inspired by simultaneous lightness contrast illusion. First two experiments contrast the size of an effect produced by the change of background color vs. the change in illumination. The third experiment deals with different type of illusions, where the effect is obtained through the appearance of multiple illumination levels. The last experiment takes into account the ratio of the target and the background. The results reveal the size of effects produced separately by the background color and illumination level and suggest the prime importance of background. Also there are other factors such as reflectance range in the scene, incremental and decremental targets, and 2D vs. 3D representation.

Luminance adaptation increased the contrast sensitivity of retinal ganglion cells

In the present study, the activity changes of chicken retinal ganglion cells in response to light stimuli with defined contrast were investigated, in the presence of various levels of sustained background illumination. Following a step increase of light illumination, the firing rate of most retinal ganglion cells increased abruptly, and then decreased to a steady-state level with a much lower firing rate during the sustained application of light. However, when a test flash was applied, which superimposed the prolonged background illumination, an increased firing rate was observed. Moreover, the neuron firing rate was increased to a greater extent when the intensity of the background illumination was higher. This may suggest that the neuron sensitivity can be modified by the background illumination level, although the neuron firing rate was reduced during sustained illumination.

Gender-dependent behavioral and sensory effects of a commercial mixture of polychlorinated biphenyls (Aroclor 1254) in rats.

Developmental exposure to polychlorinated biphenyls (PCBs) has been associated with behavioral and cognitive deficits in humans and animal models. Perinatal exposure to PCBs has also been associated with sensory deficits in animal models. These effects were hypothesized to be mediated in part by ortho-substituted PCBs, which do not or weakly bind to the aryl hydrocarbon (Ah) receptor. The present studies were designed to determine whether perinatal exposure to Aroclor 1254, a commercial mixture of > 99% ortho-substituted PCBs, would affect cognitive and sensory function in Long-Evans rats. Adult male and female offspring of female rats fed Aroclor 1254 (Lot #124-191; doses of 0, 1, or 6 mg/kg/day; gestational day 6 through postnatal day 21; n = eight/group) were trained to perform a signal detection task capable of assessing sensory thresholds. Training included autoshaping and operant conditioning. Thresholds for detecting a 1-s light stimulus were determined under background illuminations ranging from 2 lux to complete darkness. Female rats exposed to Aroclor 1254 autoshaped more rapidly than control females, at a rate akin to control males. Control females had lower thresholds than control males at all levels of background illumination. These differences were abolished by Aroclor 1254, which reduced thresholds in males and increased thresholds in females. These data extend previous findings of gender-specific effects of PCBs on neurobehavioral development to measures of acquisition and sensory function.

Background Illumination Effects upon in Vitro Conditioning in Hermissenda

In the marine snail Hemissenda, associative learning can be accomplished by paired presentations of light and vestibular stimulation. It is generally assumed that associative learning depends upon the intensity or salience of the conditioned or unconditioned stimulus (CS and US, respectively). Accordingly, during Hermissenda conditioning a stronger dark adaptation is expected to render the CS (the light) more salient and hence facilitate association. We studied the influence of background illumination level using an in vitro pairing procedure in Hermissenda. This procedure allows one to assess the effect of conditioning upon a single cell, the B photoreceptor, which is implicated in this learning process. After 15 min of adaptation to a dim background light, B photoreceptors maintained a basal rate of firing, while after adaptation to complete darkness, they stopped firing. Paired and unpaired groups received 10 training trials in either a completely dark or a dim light environment. Although a trial to trial cumulative increase in excitability was found in the paired group trained in darkness, only the paired group trained under dim background light showed a higher input resistance and cell excitability 10 min after training. These results suggest that the background dim illumination was not needed for the induction but played a role in the maintenance of the pairing effect. Possible mechanisms for such a modulatory effect are discussed.

A low noise readout detector circuit for nanoampere sensor applications

A readout detector IC has been developed which is capable of detecting nanoampere photo-current signals of interest in a high (microampere) background illumination or dc noise level (SNR=80 dB). The readout detector sensor IC processes transient signals of interest from a separate photo-diode pixel array chip. Low noise signal conditioning, filtering, and signal thresholding implement smart sensor detection of only "active pixels." This detector circuit can also be used to perform signal conditioning for other sensor applications that require detection of very small signals in a high background noise environment.