Luminous Variables Research Articles

Design and development of a low-cost angular sky luminance measurement system

Energy efficient building design requires simulated assessment of overall performance through reliable models, taking into account the daylight variations along with other significant parameters such as ventilation, plug loads and occupant behaviour. A robust indoor daylight model applicable to locations across the globe needs to incorporate local variations of sky luminance on a spatial and temporal basis, and needs an affordable system for dynamic angular daylight measurement to be used as part of a wider distributed network. In the present work, a low-cost prototype based on Light Dependent Resistors for measurement of angular daylight luminance distribution is developed and analyzed. This device was used to capture the angular analog data for 221 sky segments (20 azimuthal x 11 altitudinal segments and Zenith). The analog data was further converted to luminance data, and the visualized data was compared with sky-dome photographs and also with simulated polar daylight maps for a few Commission International de l’Eclairage (CIE) skies. The repeatability of the experiment was assessed by comparing the luminance data for selected sky segments over multiple time-segments for consecutive days. Measured data was found to be an acceptable fit with the CIE-models over various time segments, validating the prototype.

An ultraviolet study of B[e] stars: evidence for pulsations, luminous blue variable type variations and processes in envelopes

Stars with B[e] phenomenon comprise a very diverse group of objects in a different evolutionary status. These objects show common spectral characteristics, including presence of Balmer lines in emission, forbidden lines, and strong infrared excess due to the dust. The observations of emission lines indicate the illumination by ultraviolet ionizing source, which is a key part to understand the elusive nature of these objects. We study the ultraviolet variability of many B[e] stars to specify the geometry of the circumstellar environment and its variability. We analyse massive hot B[e] stars from our Galaxy and from Magellanic Clouds. We study the ultraviolet broad-band variability derived from the flux-calibrated data. We determine variations of individual lines and its correlation with the total flux variability. We detected variability of the spectral energy distribution and of the line profiles. The variability has several sources of origin, including the light absorption by the disk, pulsations, LBV-type variations, and eclipses in the case of binaries. The stellar radiation of most of B[e] stars is heavily obscured by circumstellar material. This suggests that the circumstellar material is not present only in the disk but also above its plane. The flux and line variability is consistent with a two-component model of circumstellar environment composed of the dense disk and ionized envelope. The observations of B[e] supergiants show that many of these stars have nearly the same luminosity of about $1.9\times10^{5}\,L_\odot$ and similar effective temperature.

Vernier But Not Grating Acuity Contributes to an Early Stage of Visual Word Processing.

The process of reading words depends heavily on efficient visual skills, including analyzing and decomposing basic visual features. Surprisingly, previous reading-related studies have almost exclusively focused on gross aspects of visual skills, while only very few have investigated the role of finer skills. The present study filled this gap and examined the relations of two finer visual skills measured by grating acuity (the ability to resolve periodic luminance variations across space) and Vernier acuity (the ability to detect/discriminate relative locations of features) to Chinese character-processing as measured by character form-matching and lexical decision tasks in skilled adult readers. The results showed that Vernier acuity was significantly correlated with performance in character form-matching but not visual symbol form-matching, while no correlation was found between grating acuity and character processing. Interestingly, we found no correlation of the two visual skills with lexical decision performance. These findings provide for the first time empirical evidence that the finer visual skills, particularly as reflected in Vernier acuity, may directly contribute to an early stage of hierarchical word processing.

The Importance of Spatial Visual Scene Parameters in Predicting Optimal Cone Sensitivities in Routinely Trichromatic Frugivorous Old-World Primates.

Computational models that predict the spectral sensitivities of primate cone photoreceptors have focussed only on the spectral, not spatial, dimensions. On the ecologically valid task of foraging for fruit, such models predict the M-cone (“green”) peak spectral sensitivity 10–20 nm further from the L-cone (“red”) sensitivity peak than it is in nature and assume their separation is limited by other visual constraints, such as the requirement of high-acuity spatial vision for closer M and L peak sensitivities. We explore the possibility that a spatio-chromatic analysis can better predict cone spectral tuning without appealing to other visual constraints. We build a computational model of the primate retina and simulate chromatic gratings of varying spatial frequencies using measured spectra. We then implement the case study of foveal processing in routinely trichromatic primates for the task of discriminating fruit and leaf spectra. We perform an exhaustive search for the configurations of M and L cone spectral sensitivities that optimally distinguish the colour patterns within these spectral images. Under such conditions, the model suggests that: (1) a long-wavelength limit is required to constrain the L cone spectral sensitivity to its natural position; (2) the optimal M cone peak spectral sensitivity occurs at ~525 nm, close to the observed position in nature (~535 nm); (3) spatial frequency has a small effect upon the spectral tuning of the cones; (4) a selective pressure toward less correlated M and L spectral sensitivities is provided by the need to reduce noise caused by the luminance variation that occurs in natural scenes.

English

Taking into consideration that species react differently to the substrate and luminance variations, this study aimed to evaluate the leaf content of some macronutrients and dry matter in Tabebuia aurea seedlings through the hypothesis that the growth environment can alter the concentration of chemical elements in the species. The study was conducted in a greenhouse, in randomized blocks, factorial 2 × 3 (two light intensities and three types of substrates). The first greenhouse was covered with shade cloth, with maximum flow of 950 µmol m-2 s-1 radiation, and the second was 750 µmol m-2 s-1. The substrates were: 1) Cerr. Savannah soil, 2) Ca-Mg – Savannah soil with calcium carbonate and magnesium and, 3) OM – Savannah soil with organic matter (2/1), with samples taken after 230 days of experiment. The data obtained indicated that T. aurea species has better development when grown in brighter locations in OM soils, which would be expected due to its higher nutritional content. However, when the seedlings were placed in soils with low nutrient content (Ca-Mg and Cerr.) and similar levels of potassium, plants maintained in soils with higher amounts of calcium and magnesium obtained higher growth, with greater accumulation of dry matter in leaves and total. This could indicate that the difference in growth should be related to increased amount of these Ca-Mg elements of treatment and the calcicole characteristic of the species tested. Key words: Greenhouse, seedling formation, dry matter, ipe.

Adaptive Trigonometric Transformation Function With Image Contrast and Color Enhancement: Application to Unmanned Aerial System Imagery

An unmanned aerial system (UAS)-based imaging technology has gained great interests in modern photogrammetry and remote sensing. However, due to the limitations of UAS imaging devices, image enhancement (IE) has become a necessary process for improving the visual appearance of UAS images. Although a great amount of effort has been focused on improving image quality from different aspects, the major obstacles are from computational efficiency and complexity, such as manually adjusting the associated algorithmic parameters that account for various image luminance. To overcome these drawbacks, we propose a new adaptive yet highly efficient luminance enhancement method, namely, adaptive trigonometric transformation function (ATTF), for enhancing the visual quality of digital color images captured by a UAS. The ATTF is derived from a tangent-based transformation function whose characteristics adaptively change with respect to the variation of the image luminance. By combining ATTF with a Laplacian operator and a color restoration process, a well-balanced color image is obtained. The effectiveness of the proposed technique is evaluated on various UAS-based images and compared with other IE techniques.

A luminance compensation method for fisheye video panorama stitching

The fisheye camera has becoming the most popular panoramic video capturing device. In fact, the stitching for fisheye images has drawn more and more attention. To solve the artifacts resulting from the exposure difference of several cameras, this paper proposes a luminance compensation method based on an uneven sampling histogram. According to the transition of the spatial sampling rate with the latitudes increasing in panorama, the proposed method samples the overlapped region of two adjacent images to calculate the histograms, and matches the histograms one by one to balance the luminance. Moreover, in consideration of the influence of luminance distribution to panorama video quality, we present a method for adaptive reference image selection. The selected reference image based on the proposed method can improve the overall quality of the panorama effectively. Due to the consideration of the distortion characteristics of fisheye images, the proposed method does not require an accurate alignment, and it is also well-adapted to luminance variations. Experimental results show that the proposed method can reduce the time complexity for panorama video stitching significantly without obvious quality degeneration, and it is suitable for fisheye lens-based real-time panoramic video stitching.

Luminous Flux and CCT Stabilization of White LED Device With a Bilevel Driver

The optical, color, electrical, and thermal properties of an LED devices are highly dependent on one another. The luminous flux variation and correlated color temperature (CCT) shifting of white LED sources is attributed to luminous efficacy and emission spectrum shifting with the electrical power and heat-dissipation power. An analysis model that includes the luminous flux, CCT, electrical power, and junction temperature of the white LED sources with bilevel driver is proposed in this paper. The proposed model can descript that the stablized luminous flux and CCT of the white LED system with bilevel driver is a result of the complex interactions among the given electrical power of bilevel, duty cycle, thermal resistances, junction temperature, and the physical parameters of the LED sources. Reduction variation of CCT and luminous flux of the white LED device with bilevel driver over a dimming range has been practically achieved. The proposed method can be easily adopted for improving the CCT and luminous flux stabilization of the white LED device with a bilevel driver.

Inner lips feature extraction based on CLNF with hybrid dynamic template for Cued Speech

In previous French Cued Speech (CS) studies, one of the widely used methods is painting blue color on the speaker’s lips to make lips feature extraction easier. In this paper, in order to get rid of this artifice, a novel automatic method to extract the inner lips contour of CS speakers is presented. This method is based on a recent facial contour extraction model developed in computer vision, called Constrained Local Neural Field (CLNF), which provides eight characteristic landmarks describing the inner lips contour. However, directly applied to our CS data, CLNF fails in about 41.4% of cases. Therefore, we propose two methods to correct the B parameter (aperture of inner lips) and A parameter (width of inner lips), respectively. For correcting the B parameter, a hybrid dynamic correlation template method (HD-CTM) using the first derivative of smoothed luminance variation is proposed. HD-CTM is first applied to detect the outer lower lips position. Then, the inner lower lips position is obtained by subtracting the validated lower lips thickness (VLLT). For correcting the A parameter, a periodical spline interpolation with a geometrical deformation of six CLNF inner lips landmarks is explored. Combined with an automatic round lips detector, this method is efficient to correct A parameter for round lips (the third vowel viseme made of French vowels with a small opening). HD-CTM is evaluated on 4800 images of three French speakers. It corrects about 95% CLNF errors of the B parameter, and total RMSE of one pixel (i.e., 0.05 cm on average) is achieved. The periodical spline interpolation method is tested on 927 round lips images. The total error of CLNF is reduced significantly, which is comparable to the state of the art. Moreover, the third viseme is properly distributed in the parameter A and B plane after using this method.

A dynamic colour perception system for autonomous robot navigation on unmarked roads

Abstract Navigation on unmarked and possible poorly delineated roads where the boundaries between the road and the non-road surfaces are not clearly indicated is a particularly challenging task for autonomous vehicles. The results of this study show that fairly robust navigation strategies can be generated by a robot equipped with a dynamic active-vision based control system represented by an artificial neural network synthesized using evolutionary computation techniques. In the experiments described in this paper, a simulated Pioneer robot is required to visually navigate multiple poorly delineated roads that differ in terms of variations in luminance and/or chrominance between the road and the adjacent non-road areas. Low resolution camera images are processed by a mechanism that continuously adjusts the contribution of each component of a three dimensional colour model (e.g., R, G and B) to the generation of the robot perceptual experience. We show that the best controller can successfully drive a simulated Pioneer robot in environments with colour characteristics never encountered during the design phase, and operate with colour models never used during training. We show that the dynamic differential weighting of the colour components is underpinned by a complex pattern of neural activity that allows the robot to successfully adapt its perceptual system to the colour characteristics of different visual scenes. We also show that the controller can be easily ported onto real hardware, by showing the results of a series of tests with a physical Pioneer robot required to navigate various poorly delineated pedestrian roads.

A Temporal White Noise Analysis for Extracting the Impulse Response Function of the Human Electroretinogram.

PurposeWe introduce a method for determining the impulse response function (IRF) of the ERG derived from responses to temporal white noise (TWN) stimuli.MethodsThis white noise ERG (wnERG) was recorded in participants with normal trichromatic vision to full-field (Ganzfeld) and 39.3° diameter focal stimuli at mesopic and photopic mean luminances and at different TWN contrasts. The IRF was obtained by cross-correlating the TWN stimulus with the wnERG.ResultsWe show that wnERG recordings are highly repeatable, with good signal-to-noise ratio, and do not lead to blink artifacts. The wnERG resembles a flash ERG waveform with an initial negativity (N1) followed by a positivity (P1), with amplitudes that are linearly related to stimulus contrast. These N1 and N1-P1 components showed commonalties in implicit times with the a- and b-waves of flash ERGs. There was a clear transition from rod- to cone-driven wnERGs at ∼1 photopic cd.m−2. We infer that oscillatory potentials found with the flash ERG, but not the wnERG, may reflect retinal nonlinearities due to the compression of energy into a short time period during a stimulus flash.ConclusionThe wnERG provides a new approach to study the physiology of the retina using a stimulation method with adaptation and contrast conditions similar to natural scenes to allow for independent variation of stimulus strength and mean luminance, which is not possible with the conventional flash ERG.Translational RelevanceThe white noise ERG methodology will be of benefit for clinical studies and animal models in the evaluation of hypotheses related to cellular redundancy to understand the effects of disease on specific visual pathways.

Surface Coating of Gradient Alloy Quantum Dots with Oxide Layer in White-Light-Emitting Diodes for Display Backlights.

Recently, quantum dots (QDs) have been successfully developed as efficient color converters for light-emitting diodes (LEDs) display due to excellent optical properties of QDs. Herein, we demonstrate a new approach to form metal oxide layers (or metal oxide coating) on the exterior surface of gradient alloy QDs (the most advanced chemical architecture QDs developed thus far wherein the lattice parameter from the core to shell is changing in a gradient fashion) in order to improve the photochemical stability and photoluminescence efficiency. The resulting CdO-treated QDs are incorporated into polymer matrix films to fabricate a backlight unit as a part of display panel wherein CdO-treated gradient alloy QDs are utilized as color converters upon the blue-LED excitation. The fabricated 9.7 in. iPad 2 tablet liquid crystal display panel exhibited an excellent uniformity in terms of CIE chromaticity, luminance, and bright variation and superb durability test results (maintenance of ca. 110% brightness compared to initial value even after 3 weeks of operation).

Low-Frequency Components in Rat Pial Arteriolar Rhythmic Diameter Changes

This study aimed to analyze the frequency components present in spontaneous rhythmic diameter changes in rat pial arterioles. Pial microcirculation was visualized by fluorescence microscopy. Rhythmic luminal variations were evaluated via computer-assisted methods. Spectral analysis was carried out on 30-min recordings under baseline conditions and after administration of acetylcholine (Ach), papaverine (Pap), Nω-nitro-<smlcap>L</smlcap>-arginine (<smlcap>L</smlcap>-NNA) prior to Ach, indomethacin (INDO), INDO prior to Ach, charybdotoxin and apamin, and charybdotoxin and apamin prior to Ach. Under baseline conditions all arteriolar orders showed 3 frequency components in the ranges of 0.0095-0.02, 0.02-0.06, and 0.06-0.2 Hz, another 2 in the ranges of 0.2-2.0 and 2.5-4.5 Hz, and another ultra-low-frequency component in the range of 0.001-0.0095 Hz. Ach caused a significant increase in the spectral density of the frequency components in the range of 0.001-0.2 Hz. Pap was able to slightly increase spectral density in the ranges of 0.001-0.0095 and 0.0095-0.02 Hz. <smlcap>L</smlcap>-NNA mainly attenuated arteriolar responses to Ach. INDO prior to Ach did not affect the endothelial response to Ach. Charybdotoxin and apamin, suggested as endothelium-derived hyperpolarizing factor inhibitors, reduced spectral density in the range of 0.001-0.0095 Hz before and after Ach administration. In conclusion, regulation of the blood flow distribution is due to several mechanisms, one of which is affected by charibdotoxin and apamin, modulating the vascular tone.

Medical Images Registration based on Normalized Dissimilarity Index

Image registration is an essential step in a large number of processing chains for medical images. It is used to align two images taken at different times and from different sensors as well. In this paper, we are interested in the rigid registration and similarity measures. We describe a new registration approach, based on the normalized dissimilarity index that results from the local dissimilarity map (LDP). This LDP is obtained from distance transform applied to gray-scale images, to register, undergoing a binarization. We evaluate the performance of our method compared to the classical registration measurements such as correlation and mutual information, on a medical images database. We show that the mean squared error of our approach is more accurate in comparison to the classical registration methods to which researchers still adhere. The robustness of our proposed index is validated regarding the luminance variation and the presence of "the Pepper and Salt" as much as “the Gaussian" noise.

MINIMAL ENDOILLUMINATION LEVELS AND DISPLAY LUMINOUS EMITTANCE DURING THREE-DIMENSIONAL HEADS-UP VITREORETINAL SURGERY.

To determine minimal endoillumination levels required to perform 3-dimensional heads-up vitreoretinal surgery and to correlate endoillumination levels used for measurements of heads-up display (HUD) luminous emittance. Prospective, observational surgical case series of 10 patients undergoing vitreoretinal surgery. Endoillumination levels were set to 40% of maximum output and were decreased at set intervals until the illumination level was 0%. Corresponding luminous emittance (lux) of the HUD was measured 40 cm from the display using a luxmeter (Dr. Meter, Model #LX1010BS). In 9 of 10 cases, the surgeon felt that they could operate comfortably at an endoillumination level of 10% of maximum output with corresponding HUD emittance of 14.3 ± 9.5 lux. In the remaining case, the surgeon felt comfortable at a 3% endoillumination level with corresponding HUD emittance of 15 lux. Below this threshold, subjective image dimness and digital noise limited visibility. Endoillumination levels were correlated with luminous emittance from the 3-dimensional HUD (P < 0.01). The average coefficient of variation of HUD luminance was 0.546. There were no intraoperative complications. With real-time digital processing and automated brightness control, 3-dimensional HUD platforms may allow for reduced intraoperative endoillumination levels and a theoretically reduced risk of retinal phototoxicity during vitreoretinal surgery.

The Eye Pupil's Response to Static and Dynamic Illusions of Luminosity and Darkness.

Pupil diameters were recorded with an eye-tracker while participants observed cruciform patterns of gray-scale gradients that evoked illusions of enhanced brightness (glare) or of enhanced darkness. The illusions were either presented as static images or as dynamic animations which initially appeared as a pattern of filled squares that—in a few seconds—gradually changed into gradients until the patterns were identical to the static ones. Gradients could either converge toward the center, resulting in a central region of enhanced, illusory, brightness or darkness, or oriented toward each side of the screen, resulting in the perception of a peripheral ring of illusory brightness or darkness. It was found that pupil responses to these illusions matched both the direction and intensity of perceived changes in light: Glare stimuli resulted in pupil constrictions, and darkness stimuli evoked dilations of the pupils. A second experiment found that gradients of brightness were most effective in constricting the pupils than isoluminant step-luminance, local, variations in luminance. This set of findings suggest that the eye strategically adjusts to reflect in a predictive manner, given that these brightness illusions only suggest a change in luminance when none has occurred, the content within brightness maps of the visual scene.

A New Urban Index for Expressing Inner-City Patterns Based on MODIS LST and EVI Regulated DMSP/OLS NTL

With the rapid pace of urban expansion, comprehensively understanding urban spatial patterns, built environments, green-spaces distributions, demographic distributions, and economic activities becomes more meaningful. Night Time Lights (NTL) images acquired through the Operational Linescan System of the US Defense Meteorological Satellite Program (DMSP/OLS NTL) have long been utilized to monitor urban areas and their expansion characteristics since this system detects variation in NTL emissions. However, the pixel saturation phenomenon leads to a serious limitation in mapping luminance variations in urban zones with nighttime illumination levels that approach or exceed the pixel saturation limits of OLS sensors. Consequently, we propose an NTL-based city index that utilizes the Moderate-resolution Imaging Spectroradiometer (MODIS) Land Surface Temperature (LST) and Enhanced Vegetation Index (EVI) images to regulate and compensate for desaturation on NTL images acquired from corresponding urban areas. The regulated results achieve good performance in differentiating central business districts (CBDs), airports, and urban green spaces. Consequently, these derived imageries could effectively convey the structural details of urban cores. In addition, compared with the Vegetation Adjusted NTL Urban Index (VANUI), LST-and-EVI-regulated-NTL-city index (LERNCI) reveals superior capability in delineating the spatial structures of selected metropolis areas across the world, especially in the large cities of developing countries. The currently available results indicate that LERNCI corresponds better to city spatial patterns. Moreover, LERNCI displays a remarkably better “goodness-of-fit” correspondence with both the Version 1 Nighttime Visible Infrared Imaging Radiometer Suite Day/Night Band Composite (NPP/VIIRS DNB) data and the WorldPop population-density data compared with the VANUI imageries. Thus, LERNCI can act as a helpful indicator for differentiating and classifying regional economic activities, population aggregations, and energy-consumption and city-expansion patterns. LERNCI can also serve as a valuable auxiliary reference for decision-making processes that concern subjects such as urban planning and easing the central functions of metropolis.

Visual discomfort and flicker

Flickering lights can be uncomfortable to look at and can induce seizures in observers with photosensitive epilepsy. However, the temporal characteristics contributing to these effects are not fully known. In the spatial domain, one identified source of visual discomfort is when images have Fourier amplitude spectra that deviate from the natural (∼1/frequency, 1/f) statistical characteristics of natural scenes, especially if they contain excess energy at the medium frequencies at which the visual system is most sensitive. We tested for analogous effects in the temporal domain, manipulating both the amplitude and phase spectra of the flicker. Participants judged the relative discomfort of temporal luminance variations in a pair of uniform 17° fields with different temporal modulations. In general, discomfort increased with deviations from natural amplitude spectra, particularly those with excess energy at medium frequencies or biased toward sharper spectra. These ratings of discomfort were also consistent with ratings of how natural the modulations appeared. However, the temporal discomfort judgments were also strongly affected by the phase spectra of the flicker, with fixed vs. random spectra producing very different responses. This was not due to the perceived regularity or predictability of the flicker, but could arise from a number of other potential factors. Our findings suggest that, like spatial patterns, visual discomfort in time-varying patterns depends in part on how similar they are to the amplitude spectra of temporal variations in the natural visual environment, but also point to the critical role of the phase spectrum in the perceived discomfort of flicker.

Dual-dissimilarity measure-based statistical video cut detection

Video cut detection is an essential process of temporal continuity-based video applications such as video segmentation, video retargeting, and frame rate up-conversion. The performance of these applications highly depends on the performance of cut detection. This paper proposes an effective and low-complexity approach for detecting video cuts. The proposed method uses two simple dissimilarity measures for video cut detection: inter-frame luminance variation and temporal variation of inter-frame variations over several frames. The first is used to detect abrupt changes, and the second is used to reduce the influence of disturbances, e.g., object or camera motion. The proposed method is comprised of the following three steps. First, it computes the two dissimilarity measures. Then, it combines them using Bayesian estimation and linear regression. Finally, it decides on the possibility of cuts using the combined dissimilarity measure. Experimental results show that the average F1 score of the proposed method was up to 0.252 (37.0%) higher than those of the benchmark methods. Moreover, the algorithmic simplicity of the proposed method reduced the average computation time per pixel by up to 99.8%, when compared with state-of-the-art methods. Thus, the proposed method is superior to existing methods in terms of computational complexity and detection accuracy.

Morphological Analysis (SEM) of the Surface of a Non-Noble Dental Alloy Subjected to Electrocorrosion

Corrosion consists in the degradation of a material under the chemical or electrochemical action of the environment where it is placed. The investigations carried out aimed to show the structural modifications produced in Co-Cr-Mo alloy, Robur 400 (Eisenbacher Dental – Waren ED GmbH, Germany) subjected to electrocorrosion in Fusayama-Mayer artificial saliva. The specimens prepared by mechanical polishing were analysed structurally by using a scanning electron microscope. During the tests run we could notice a general corrosion of the surfaces of the specimens made from Robur alloy. Through 2D and 3D microscopy and qualitative determinations of the luminous variation we could notice the effects of electrocorrosion tests on the surface of the metal material.