Ambient Light Environment Research Articles

Spread spectrum lighting for excitation-emission matrix measurements in ambient light environments

Spread spectrum lighting for excitation-emission matrix measurements in ambient light environments

Event fusion photometric stereo network

Photometric stereo methods typically rely on RGB cameras and are usually performed in a dark room to avoid ambient illumination. Ambient illumination poses a great challenge in photometric stereo due to the restricted dynamic range of the RGB cameras. To address this limitation, we present a novel method, namely Event Fusion Photometric Stereo Network (EFPS-Net), which estimates the surface normals of an object in an ambient light environment by utilizing a deep fusion of RGB and event cameras. The high dynamic range of event cameras provides a broader perspective of light representations that RGB cameras cannot provide. Specifically, we propose an event interpolation method to obtain ample light information, which enables precise estimation of the surface normals of an object. By using RGB-event fused observation maps, our EFPS-Net outperforms previous state-of-the-art methods that depend only on RGB frames, resulting in a 7.94% reduction in mean average error. In addition, we curate a novel photometric stereo dataset by capturing objects with RGB and event cameras under numerous ambient light environments.

50‐4: Late‐News Paper: Multi‐domain Retarders for Eliminating Off‐axis Reflection Color Differences in Automotive OLED Displays

A two‐domain quarter‐wave retarder is employed as one layer of the circular polarizer to compensate for the retardation dependent on the incident angles. The reflective color differences of the panel between normal and oblique directions can be completely eliminated in an ambient light environment because of the effects of the multi‐domain retarder.

Influence of ambient water coloration on habitat and conspecific choice in the female Lake Malawi cichlid, Metriaclima zebra.

Female cichlid fish living in African great lakes are known to have sensory systems that are adapted to ambient light environments. These sensory system adaptations are hypothesized to have influenced the evolution of the diverse male nuptial coloration. In rock-dwelling Lake Malawi mbuna cichlids, however, the extent to which ambient light environments influence female sensory systems and potentially associated male nuptial coloration remains unknown. Yet, the ubiquitous blue flank coloration and UV reflection of male mbuna cichlids suggest the potential impacts of the blue-shifted ambient light environment on these cichlid's visual perception and male nuptial coloration in the shallow water depth in Lake Malawi. In the present study, we explored whether and how the sensory bias of females influences intersexual communication in the mbuna cichlid, Metriaclima zebra. A series of choice experiments in various light environments showed that M. zebra females 1) have a preference for the blue-shifted light environment, 2) prefer to interact with males in blue-shifted light environments, 3) do not show a preference between dominant and subordinate males in full-spectrum, long-wavelength filtered, and short-wavelength filtered light environments, and 4) show a "reversed" preference for subordinate males in the UV-filtered light environment. These results suggest that the visual perception of M. zebra females may be biased to the ambient light spectra in their natural habitat by local adaptation and that this sensory bias may influence the evolution of blue and UV reflective patterns in male nuptial coloration.

Metamaterial grating for colorimetric chemical sensing applications

We propose and demonstrate a metamaterial grating sensor (MGS) composed of gold (Au) nanograting on a silver (Ag) thin-film and then encapsulated with a polydimethylsiloxane (PDMS) microfluidic chip for colorimetric chemical sensing applications. MGS is sensitive to the wavevector of incident light owing to the surface plasmonic resonance of metamaterial grating results in specific reflected colors of MGS affected by background refractive index (n) and incident angle (θ). The measured reflection spectra of MGS exhibit angle-dependence characteristic by changing θ value from 10° to 45°, whose resonances are blue-shifted 80 nm from the wavelength of 691 nm–611 nm and 88 nm from the wavelength of 671 nm–583 nm by injecting isopropyl alcohol (IPA) and deionized (DI) water solutions into MGS, respectively. This angle-dependence characteristic of MGS is visual in ambient light. Moreover, by injecting IPA solution with different concentrations, the maximum sensitivity of reflected resonance to n value is 1474 nm/RIU at θ = 45°. Similarly, the reflected color shows green, yellow, dark yellow, and cyan colors for MGS covering with DI water, acetone, 1 ppm lapatinib in acetone, and IPA solutions, respectively in the ambient light environment. The proposed MGS proves the potential applications in portable and convenient biochemical sensing without spectrometers.

Elimination of ambient light reflection color in automotive organic light emitting diode displays

A simple method for eliminating reflective color differences that depend on the viewing angle in automotive organic light emitting diode display panels is reported. A two-domain quarter-wave retarder is employed as one layer of the circular polarizer to compensate for the retardation resulting from the incident angles. The reflective color differences of the panel between normal and oblique directions can be completely eliminated in an ambient light environment because of the effects of the multidomain retarder. Additionally, the two-domain quarter-wave retarder induces a symmetric reflectance distribution on the viewing angles, resulting in outstanding reflective properties.

Visual Background Choice and Light Environment Affect Male Guppy Visual Contrast.

Male guppies (Poecilia reticulata) have multiple colored spots and perform courtship displays near the edges of streams in Trinidad in shallow water flowing through rainforest. Depending upon the orientation of the pair, the female sees the male displays against gravel or other stream bed substrates or against the spacelight—the roughly uniform light coming from the water column away from the bank. We observed courting pairs in two adjacent natural streams and noted the directions of each male display. We found that the female sees the male more often against spacelight than against gravel when females either faced the spacelight from the opposite bank or from downstream, or both. Visual modelling using natural substrate reflectances and field light measurements showed higher chromatic contrast of males against spacelight than against substrates independent of the two ambient light environments used during displays, but achromatic contrast depended upon the ambient light habitat. This suggests that courtship involves both chromatic and achromatic contrast. We conclude that the orientation of courting pairs and the ambient light spectrum should be accounted for in studies of mate choice, because the visual background and light affect visibility, and these differ with orientation.

Photosynthetic Efficiency and Leaf Traits of Shorea leprosula Grown Under the Sun and Shade Conditions in Lentang Forest Reserve

Rehabilitation of degraded forests can be a huge challenge as these areas usually face problems including weed invasion, nutrient-deficient soil, lack of seed source and inability of native tree species to colonise or regenerate naturally. Human intervention is thus needed to accelerate the process of rehabilitation. In this regard, using the right species is as important as providing the right environment to encourage the survival and establishment of seedlings. Therefore, the aim of this study was to compare the photosynthetic characteristics and leaf traits of Shorea leprosula trees grown under the sun and shaded environments in a degraded forest. Shade trees were found to have about 20% higher leaf dry weight and 5% higher leaf area as well as significantly (p < 0.05) more chlorophyll than leaves on sun trees. Leaves in shade trees attained maximum photosynthesis at lower photosynthetic photon flux density (PPFD) compared to sun trees. When comparing both sun and shade trees, fast chlorophyll induction curve showed no significant differences in maximum quantum yield of PSII photochemistry (Fv/Fm) and thus was almost unaffected by the leaf ambient light environment. This indicated that although shade trees received lower light intensity compared to sun trees, the physiological responses indicated that the former were capable of minimising light limitation through foliar morphological and physiological adaptations. Our results thus suggested that S. leprosula, being an economically valuable timber species, can be planted in areas with partial shade or in gaps for the purpose of rehabilitation.

Deep Spatio-Temporal Illuminant Estimation Under Time-Varying AC Lights

Artificial lights, which are powered by alternating current (AC), are ubiquitous nowadays. The intensity of these lights fluctuates dynamically depending on the AC power. In contrast to previous color constancy methods that exploited the spatial color information, we propose a novel deep learning-based color constancy method that exploits the temporal variations exhibited by AC-powered lights. Using a high-speed camera, we capture the intensity variations of AC lights. Then, we use these variations as an important cue for illuminant learning. We propose a network composed of spatial and temporal branches to train the model with both spatial and temporal features. The spatial branch learns the conventional spatial features from a single image, whereas the temporal branch learns the temporal features of AC-induced light intensity variations in a high-speed video. The proposed method calculates the temporal correlation between the high-speed frames to extract the effective temporal features. The calculations are done at a low computational cost and the output is fed into the temporal branch to help the model concentrate on illuminant-attentive regions. By learning both spatial and temporal features, the proposed method performs remarkably under a complex illuminant environment in a real world scenario in which color constancy is difficult to investigate. The experimental results demonstrate that the proposed method produces lower angular error than the previous state-of-the-art by 30%, and works exceptionally well under various illuminants, including complex ambient light environments.

Ambient ultraviolet B radiation induced valve behavioral acclimation of Pacific oyster which resulted from the different response strategies of smooth and striated adductor muscles

Light not only conveys image-forming vision but also has an impact on various physiological functions. In particular, ultraviolet B (UVB) radiation has the closest relationship with living organisms. For Pacific oysters (Crassostrea gigas), alteration of valve behavior is one of the most important ways responding to ambient UVB. In the present study, the response of adult C. gigas to sunlight (especially UVB) was evaluated by monitoring valve activity and further elucidated at the physiological and metabolomic levels. After exposure, the valve activity of C. gigas demonstrated flexible acclimation to the ambient conditions. The potential adjustment of osmoregulation and oxidative stress might be related to ambient UVB radiation. Mycosporine-like amino acids might contribute to the protection of C. gigas against UVB, while precursors of β-alanine and degradation products of 5-hydroxytryptamine might adjust the contraction of the adductor muscles. The different responses of the adductor muscles (smooth and striated) were manifested in signal transduction and metabolisms of energy and nucleotide. This study not only indicated the correlation between the valve behavioral changes in oysters and light radiation, especially UVB, but illustrated the acclimation strategies of oysters to ambient light (UVB) environment.

Photophysiological cycles in Arctic krill are entrained by weak midday twilight during the Polar Night.

Light plays a fundamental role in the ecology of organisms in nearly all habitats on Earth and is central for processes such as vision and the entrainment of the circadian clock. The poles represent extreme light regimes with an annual light cycle including periods of Midnight Sun and Polar Night. The Arctic Ocean extends to the North Pole, and marine light extremes reach their maximum extent in this habitat. During the Polar Night, traditional definitions of day and night and seasonal photoperiod become irrelevant since there are only “twilight” periods defined by the sun’s elevation below the horizon at midday; we term this “midday twilight.” Here, we characterize light across a latitudinal gradient (76.5° N to 81° N) during Polar Night in January. Our light measurements demonstrate that the classical solar diel light cycle dominant at lower latitudes is modulated during Arctic Polar Night by lunar and auroral components. We therefore question whether this particular ambient light environment is relevant to behavioral and visual processes. We reveal from acoustic field observations that the zooplankton community is undergoing diel vertical migration (DVM) behavior. Furthermore, using electroretinogram (ERG) recording under constant darkness, we show that the main migratory species, Arctic krill (Thysanoessa inermis) show endogenous increases in visual sensitivity during the subjective night. This change in sensitivity is comparable to that under exogenous dim light acclimations, although differences in speed of vision suggest separate mechanisms. We conclude that the extremely weak midday twilight experienced by krill at high latitudes during the darkest parts of the year has physiological and ecological relevance.

SUMOylation of different targets fine-tunes phytochrome signaling.

Plants monitor their surrounding ambient light environment by specialized photoreceptor proteins. Among them, phytochromes monitor red and far-red light. These molecules perceive photons, undergo a conformational change, and regulate diverse light signaling pathways, resulting in the mediation of key developmental and growth responses throughout the whole life of plants. Posttranslational modifications of the photoreceptors and their signaling partners may modify their function. For example, the regulatory role of phosphorylation has been investigated for decades by using different methodological approaches. In the past few years, a set of studies revealed that ubiquitin-like short protein molecules, called small ubiquitin-like modifiers (SUMOs) are attached reversibly to different members of phytochrome signaling pathways, including phytochromeB, the dominant receptor of red light signaling. Furthermore, SUMO attachment modifies the action of the target proteins, leading to altered light signaling and photomorphogenesis. This review summarizes recent results regarding SUMOylation of various target proteins, the regulation of their SUMOylation level, and the physiological consequences of SUMO attachment. Potential future research directions are also discussed.

Non-Contact Oxygen Saturation Measurement Using YCgCr Color Space with an RGB Camera.

Oxygen saturation (SPO2) is an important indicator of health, and is usually measured by placing a pulse oximeter in contact with a finger or earlobe. However, this method has a problem in that the skin and the sensor must be in contact, and an additional light source is required. To solve these problems, we propose a non-contact oxygen saturation measurement technique that uses a single RGB camera in an ambient light environment. Utilizing the fact that oxygenated and deoxygenated hemoglobin have opposite absorption coefficients at green and red wavelengths, the color space of photoplethysmographic (PPG) signals recorded from the faces of study participants were converted to the YCgCr color space. Substituting the peaks and valleys extracted from the converted Cg and Cr PPG signals into the Beer–Lambert law yields the SPO2 via a linear equation. When the non-contact SPO2 measurement value was evaluated based on the reference SPO2 measured with a pulse oximeter, the mean absolute error was 0.537, the root mean square error was 0.692, the Pearson correlation coefficient was 0.86, the cosine similarity was 0.99, and the intraclass correlation coefficient was 0.922. These results confirm the feasibility of non-contact SPO2 measurements.

Biodistribution of adeno-associated virus type 2 carrying multi-characteristic opsin in dogs following intravitreal injection.

Gene therapy of retinal diseases using recombinant adeno‐associated virus (rAAV) vector‐based delivery has shown clinical success, and clinical trials based on rAAV‐based optogenetic therapies are currently in progress. Recently, we have developed multi‐characteristic opsin (MCO), which has been shown to effectively re‐photosensitize photoreceptor‐degenerated retina in mice leading to vision restoration at ambient light environment. Here, we report the biodistribution of the rAAV2 carried MCO (vMCO‐I) in live samples and post‐mortem organs following intraocular delivery in wild‐type dogs. Immunohistochemistry showed that the intravitreal injection of vMCO‐I resulted in gene transduction in the inner nuclear layer (INL) but did not induce detectable inflammatory or immune reaction in the dog retina. Vector DNA analysis of live body wastes and body fluids such as saliva and nasal secretions using quantitative polymerase chain reaction (qPCR) showed no correlative increase of vector copy in nasal secretions or saliva, minimal increase of vector copy in urine in the low‐dose group 13 weeks after injection and in the faeces of the high‐dose group at 3–13 weeks after injection suggesting clearance of the virus vector via urine and faeces. Further analysis of vector DNA extracted from faeces using PCR showed no transgene after 3 weeks post‐injection. Intravitreal injection of vMCO‐I resulted in few sporadic off‐target presences of the vector in the mesenteric lymph node, liver, spleen and testis. This study showed that intravitreal rAAV2‐based delivery of MCO‐I for retinal gene therapy is safe.

Single-photon detection for MIMO underwater wireless optical communication enabled by arrayed LEDs and SiPMs.

Underwater wireless optical communication (UWOC) is a promising technology that can be a candidate to improve the communication capacity and speed in aquatic media. The aim of this study is to examine the performance of a silicon photomultiplier (SiPM) array-based multiple-input multiple-output (MIMO) UWOC system. A SiPM is a modern solid-state photodetector with extremely high sensitivity up to the single-photon level or a photon-counting ability, which helps in detecting extremely weak light signals after long-distance underwater channel attenuation. We clarify the basic characteristics and photon-counting detection mode of a SiPM. In particular, the photocount of a SiPM is approximated by a Gaussian distribution, and theoretical analysis shows that only 13.3 photons need to be detected during "1" symbol period to achieve a bit error rate of 10-3 in an ambient light environment. Moreover, a SiPM also has a better analog mode detection ability than an avalanche photodiode (APD) and realizes 2 Mbps analog communication owing to its unique array structure and high photon detection efficiency. Furthermore, MIMO, i.e., spatial diversity, is applied as an effective method to relax the link alignment, improve the system performance, and alleviate the effect of optical turbulence. In our experiment, with a photon-counting 6×3 MIMO scheme, an energy per bit of 7.38×10-9 J/bit is achieved at a scintillation index of 4.66×10-3 in a 10 m water tank with 1 Mbps on-off-keying (OOK) modulation. To the best of our knowledge, this is the first study on a MIMO-UWOC system based on the photon-counting mode of a SiPM array. This UWOC system combines the advantages of SiPMs and the MIMO scheme and has the potential to realize long-distance UWOC under optical turbulence.

Employment of artificial neural networks for non-invasive estimation of leaf water status using color features: a case study in Spathiphyllum wallisii

The potential of combining artificial neural networks (ANNs) and image processing for assessing leaf relative water content (RWC) and water content (WC) was addressed. Spathiphyllum wallisii was employed as model species, because it has broad leaves and very responsive stomata. In the course of desiccation, leaves were periodically weighted (to calculate RWC and WC conventionally) and imaged. Image acquisition was performed by a scanner, and was, thus, independent of ambient light environment. Color feature extraction was performed in three color spaces (RGB, HSI, and CIELAB), while six texture statistical features were calculated for each of the (nine) computed color channels. Prior to model development via ANNs, the obtained feature vector underwent feature reduction using principal component analysis. The presented methodology yielded very precise estimations of leaf RWC and WC (correlation coefficient > 0.95). Therefore, the technique under study was proven to be very promising for non-invasive in situ measurements of leaf water status.

Learning digital camera pipeline for extreme low-light imaging

In low-light conditions, a conventional camera imaging pipeline produces sub-optimal images that are usually dark and noisy due to a low photon count and low signal-to-noise ratio (SNR). We present a data-driven approach that learns the desired properties of well-exposed images and reflects them in images that are captured in extremely low ambient light environments, thereby significantly improving the visual quality of these low-light images. The recent works on this problem only consider a pixel-level loss metric that ignores perceptual quality and thus generate outputs susceptible to visual artifacts. To address this problem, we propose a new loss function that exploits the characteristics of both pixel-wise and perceptual metrics, enabling our deep neural network to learn the camera processing pipeline to transform the short-exposure, low-light RAW sensor data to well-exposed sRGB images. The results show that our method outperforms the state-of-the-art according to psychophysical tests as well as pixel-wise standard metrics and recent learning-based perceptual image quality measures. In essence, the proposed model can potentially replace the conventional digital camera pipeline for the specific case of extreme low-light imaging.

Distribution and photosynthetic assimilation of rosulate aroid epiphytes in a Costa Rican lowland rainforest

Relatively few studies are available to characterize the distribution, abundance and ecophysiology of aroid epiphytes, distinct from aroid hemiepiphytes which are more common and abundant. The rosulate growth form is restricted to a relatively small number of aroid species. Field and experimental growth studies and ecophysiological measurements on rosulate aroids were carried out at La Selva Biological Station in the premontane rainforest of the Atlantic lowlands of Costa Rica. Rosulate aroids occur in habitats from forest understory to high canopy, and from old growth wet forest to secondary forest in Costa Rica. The distribution of rosulate and acaulescent aroid epiphytes were determined in multiple stands of old growth and secondary tropical forests at La Selva. Anthurium upalense and Philodendron wendlandii exhibited a preference for upper canopies on trees over 50 cm dbh where irradiance levels are high for much of the day. Anthurium consobrinum and A. bakeri occurred lower in the canopy in more shaded positions. To evaluate how these habitat preferences are related to plant traits, controlled shadehouse growth experiments were conducted to characterize species response to different ambient light environments. We applied conditions of high light (50% full sun), medium light (10% full sun), and low light (2% full sun) to simulate a gradient of canopy and understory light environments. Anthurium consobrinum and A. bakeri exhibited photosynthetic traits characteristic of shade-adapted understory epiphytes. In contrast, A. upalense and Ph. wendlandii, typically high canopy species, had maximum photosynthetic rates of 10.5 and 8.7 µmol m−2 s−1, respectively, higher than those previously reported for other vascular epiphytes. The variability in distribution of epiphytic aroids in Costa Rican premontane rainforest is consistent with their diversity of ecological and ecophysiological traits demonstrating adaptation to diverse canopy habitats in this aroid growth form.

A robust photoplethysmographic imaging for contactless heart and respiratory rates measurement using a simple webcam

Video photoplethysmography has been an area of interest for researchers from different domains driven by the demand of low cost, comfortable, simple and portable technology for physiological parameters measurements. In this paper we propose a robust and simple method for remotely measure heart and respiratory activities through video photoplethysmographic (vPPG) signal recordings using a low-cost webcam. The vPPG signal is extracted from colour video recording of a human face in an ambient light environment. The image and signal processing operations are minimised and optimised. Three critical aspects which are performances, reduced computational time and low computational complexity are focused. Experimental heart rate, breathing rate, and heart rate variability obtained results on 20 healthy subjects show a high correlation with those obtained using an approved contact sensor. The heart rate error obtained with the proposed method is ±2 beats per minute (bpm), this value is acceptable for standard heart diagnosis diseases.

Blue Light Exposure Effects on Sleep Attributes in a 72-Hour Military Exercise

In the digital age, the military is developing cutting edge technologies (e.g., heads-up and mixed reality displays, night vision devices, etc.) to maximize situational awareness and effectiveness. Effects of light exposure from screen-based systems on our Soldier-operators has not been fully considered. Some literature concludes that evening blue light exposure preceding bedtime can result in increased alertness and may negatively impact sleep, producing negative moodstates and sleepiness upon wakening. The current study looks at blue light exposure and subsequent sleep of forty-six Soldiers during a company-wide field exercise utilizing wrist-worn actigraphy and light sensors. Observations indicate periods of blue light exposure during evening field operations were followed by sleep intervals with significant decrements in sleep quality. Future studies will isolate the effects of military-specific blue light emitting device exposure in high contrast, low ambient light environments on sleep quality, providing specific guidance and interventions to reduce negative impacts on operations.