Luminous Variables Research Articles

A Temperature Compensation Method by Adjusting Gamma Voltages for High Luminance Uniformity of Active Matrix Organic Light-Emitting Diode Displays

In this paper, a temperature compensation method is proposed for active-matrix organic light-emitting diode (AMOLED) displays to achieve high luminance uniformity over a wide operating temperature range. The proposed temperature compensation method compensates for variation in OLED luminance according to temperature by adjusting the gamma voltages. To verify the proposed method, a built-in test circuit, which includes temperature sensors, current calculation block, current adjustment block, and gamma voltage generator, was fabricated using 90 nm complementary metal-oxide semiconductor process technology with 6 V high-voltage devices. The measurement results show that the proposed method achieves a high luminance uniformity with an OLED luminance variation of less than 1.54 cd/m 2 over the temperature range of -45°C to 60°C. Therefore, the proposed temperature compensation method is suitable for AMOLED displays requiring high luminance uniformity.

Perceived Dark Rim Artifact in First-Pass Myocardial Perfusion Magnetic Resonance Imaging Due to Visual Illusion.

To demonstrate that human visual illusion can contribute to sub-endocardial dark rim artifact in contrast-enhanced myocardial perfusion magnetic resonance images. Numerical phantoms were generated to simulate the first-passage of contrast agent in the heart, and rendered in conventional gray scale as well as in color scale with reduced luminance variation. Cardiac perfusion images were acquired from two healthy volunteers, and were displayed by the same gray and color scales used in the numerical study. Before and after k-space windowing, the left ventricle (LV)-myocardium boarders were analyzed visually and quantitatively through intensity profiles perpendicular the boarders. k-space windowing yielded monotonically decreasing signal intensity near the LV-myocardium boarder in the phantom images, as confirmed by negative finite difference values near the board ranging -1.07 to -0.14. However, the dark band still appears, which is perceived by visual illusion. Dark rim is perceived in the in-vivo images after k-space windowing that removed the quantitative signal dip, suggesting that the perceived dark rim is a visual illusion. The perceived dark rim is stronger at peak LV enhancement than the peak myocardial enhancement, due to the larger intensity difference between LV and myocardium. In both numerical phantom and in-vivo images, the illusory dark band is not visible in the color map due to reduced luminance variation. Visual illusion is another potential cause of dark rim artifact in contrast-enhanced myocardial perfusion MRI as demonstrated by illusory rim perceived in the absence of quantitative intensity undershoot.

Driving risk assessment using driving behavior data under continuous tunnel environment

Objective: Driving behavior is the key feature for determining the nature of traffic stream qualities and reflecting the risk of operating environments. However, evaluating the driving risk accurately and practically in continuous tunnels (tunnels with a space more than 250 m and less than 1000 m) still faces severe challenges due to the complex driving conditions. The objective of this study is to predict the driving risk indicators and determine different risk levels.Methods: The naturalistic driving system equipped with a road environment and driving behavior data acquisition system combined with the fixed-point test method was used for data collection in 130 tunnels on four highways. A traditional AASHTO braking model and convex hull algorithm were adopted to predict the critical safety speed and the critical time headway of each risk feature point in tunnels. According to the risk constraints under free-flow, car-following and lane-changing conditions, the average traffic flow risk index (TFRI) representing six risk levels and the safety threshold of the corresponding risk indicators were determined.Results: The findings of this study revealed that the critical safety speed at nighttime is slower than in other daytime conditions in continuous tunnels. The time headway slightly changes under 90 km/h. As the speed continues to increase, speed has a significant influence on the critical time headway. The only reliable interaction involved the different adverse weather conditions on the mean critical safety speed in the continuous tunnels (short plus long) (F = 9.730, p＜0.05) and single long tunnels (F = 12.365, p＜0.05).Conclusions: It can be concluded that driving behaviors significantly vary in different tunnel risk feature points and the combined effect of high speed and luminance variation may result in high driving risk. The performance validation indicted that the risk assessment level determined by the proposed approach is consistent with the real safety situations. The study provides an effective and generally acceptable method for identifying driving risk criteria that can also be applied for traffic management and safety countermeasures with a view to possible implementation in continuous tunnels.

Adaptation luminance variation under lamps of different spectral compositions with variable surrounding luminance effects

The mesopic photometry system is expected to enable lighting designers to provide more visually effective lighting designs for appropriate outdoor lighting applications which are supposed to be more energy efficient compared to the photopic system. Studies on the adaptation characteristics are performed to define adaptation luminance and viewing conditions on the basis of peripheral adaptation state of observers for implementation of mesopic photometry system in outdoor lighting. In this work, experimentation is carried out to study the change in adaptation luminance due to various combinations of lamps with different spectral compositions and variable surrounding luminance effects caused by warm white and cool white light sources. The analysis of experimental results reveals that adaptation luminance can be considered instead of mesopic luminance for fixed area of measurement. Spectral composition of surrounding light sources imparts significant contribution on adaptation luminance. Cool white LED lamp shows most effective adaptation luminance under cool white surrounding lighting effect.

Image processing analysis of oral cancer, oral potentially malignant disorders, and other oral diseases using optical instruments

Oral cancer screening is important for early detection and early treatment, which help improve survival rates. Biopsy is invasive and painful, while fluorescence visualization using optical instruments is non-invasive, convenient, and provides results in real time, and examinations can be repeated. The purpose of this study was to determine the usefulness of optical instruments in oral screening. A total of 314 patients who were examined using optical instruments at Tokyo Dental College between 2014 and 2018 were enrolled in this study. Fluorescence visualization images were analyzed using subjective and objective evaluations. Subjective evaluation for detecting oral cancer offered 98.0% sensitivity and 43.2% specificity. Regarding the objective evaluations for detecting oral cancer, sensitivity and specificity were 61.9% and 62.7% for mean luminance, 90.3% and 55.7% for luminance ratio, 56.5% and 67.7% for standard deviation of luminance, and 72.5% and 85.4% for coefficient of variation of luminance. Fluorescence visualization with subjective and objective evaluation using optical instruments is useful for oral cancer screening.

The redder the better? Information content of red skin coloration in female Japanese macaques

Primates appear unusual among mammals in the expression of female colorful ornaments in the absence of sex role reversal. Most studies of female ornamentation in primates have focused on the sexual signaling function of female exaggerated ano-genital swellings in female-female competition and male attraction, but other female colorful ornaments, such as red skin coloration, may also contain information about reproductive status and individual characteristics. We analyzed variation in facial and hindquarter coloration (redness and luminance) according to the timing of the fertile phase (intra-cycle variation), the cycle number, whether the cycle was conceptive or non-conceptive (inter-cycle variation), and in relation to individual characteristics (social rank, parity, and body mass) in 12 captive female Japanese macaques (Macaca fuscata). While facial and hindquarter coloration did not accurately indicate the timing of the fertile phase, variation in hindquarter luminance signaled perceptible differences between pre- and post-ovulation stages. Hindquarters became less red, and faces were lighter as the number of consecutive cycles increased. Hindquarters were redder during non-conceptive cycles compared with conceptive ones. Individual variation in skin redness and luminance appeared perceptible under good light conditions. Higher-ranking females had darker hindquarters. We also found that variation in female skin coloration may contain information about differences in body mass but not in parity. Female skin coloration in Japanese macaques may thus be more indicative of inter-cycle variation and various specific female characteristics than the timing of the fertile phase. Our study provides insight into the potential information content of this signal and demonstrates the characteristics that males might be selecting for should males prefer redder females. Primates are the most colorful group of mammals. Females of some primate species display red skin color that is suggested to play a role in mate attraction by reflecting reproductive status or individual characteristics. In Japanese macaques, a species lacking accurate behavioral and auditory indices of the probability of ovulation, female red skin coloration (face and hindquarters) may influence mating activity. Our study shows that this colorful trait does not contain information about the timing of the fertile phase and parity but may indicate inter-cycle differences and some female characteristics. Our findings add to a growing body of research on the possible roles and functions of female colorful ornaments in animal sexual communication.

SEM/EDS analyses on shape memory alloy subjected to electrochemical corrosion

The aim of the present paper was to investigate the modifications occurred in the Ti-based shape memory alloy subject to electrochemical corrosion in artificial saliva. By 2D and 3D microscopy and by qualitative determinations of the luminous variation we could notice the effects of electrochemical corrosion tests on the surface of the metallic material, and by EDS determinations (Line and Mapping modes) of the surface chemical composition we could determine the chemical modifications produced following the corrosion tests.

Differences in Stereoscopic Luster Evoked by Static and Dynamic Stimuli.

We compared the classic static stereoscopic luster phenomenon with a recently described dynamic variant (“counter modulation”) to investigate whether they are related to the same or different processes. In the experiments, we presented pairs of center-surround stimuli haploscopically and measured the effect of the contrast between center colors on perceived luster. The center colors were either static or temporally modulated. In addition, we examined five color conditions (one achromatic, two equiluminant, and two mixed conditions) and three background conditions that influence the channel-wise polarities of the contrast of the two centers to the common surround. The results for static and dynamic stimuli differed in several ways, suggesting that they depend on different mechanisms: Compared with the static version, in dynamic stimuli, luster was perceived at markedly lower contrasts, did not depend on the sign of the contrast polarities, and appeared more steady. However, both phenomena seem also similar in some respects: In both cases, equiluminant stimuli led to lustrous impressions that were considerably less strong than those evoked by stimuli containing luminance variation, and the strength of the perceived luster was generally boosted with reversed contrast polarities.

Unravelling purinergic regulation in the epididymis: activation of V-ATPase-dependent acidification by luminal ATP and adenosine.

In the epididymis, elaborate communication networks between epithelial cells are important with respect to establishing an optimal acidic luminal environment for the maturation and storage of spermatozoa, which is essential for male fertility. Proton secretion by epididymal clear cells is achieved via the proton pumping V-ATPase located in their apical membrane. In the present study, we dissect the molecular mechanisms by which clear cells respond to luminal ATP and adenosine to modulate their acidifying activity via the adenosine receptor ADORA2B and the pH-sensitive ATP receptor P2X4. We demonstrate that the hydrolysis of ATP to produce adenosine by ectonucleotidases plays a key role in V-ATPase-dependent proton secretion, and is part of a feedback loop that ensures acidification of the luminal compartment These results help us better understand how professional proton-secreting cells respond to extracellular cues to modulate their functions, and how they communicate with neighbouring cells. Cell-cell cross-talk is crucial for the dynamic function of epithelia, although how epithelial cells detect and respond to variations in extracellular stimuli to modulate their environment remains incompletely understood. In the present study, we used the epididymis as a model system to investigate epithelial cell regulation by luminal factors. In the epididymis, elaborate communication networks between the different epithelial cell types are important for establishing an optimal acidic luminal environment for the maturation and storage of spermatozoa. In particular, clear cells (CCs) secrete protons into the lumen via the proton pumping V-ATPase located in their apical membrane, a process that is activated by luminal alkalinization. However, how CCs detect luminal pH variations to modulate their function remains uncharacterized. Purinergic regulation of epithelial transport is modulated by extracellular pH in other tissues. In the present study, functional analysis of the mouse cauda epididymis perfused in vivo showed that luminal ATP and adenosine modulate the acidifying activity of CCs via the purinergic ADORA2B and P2X4 receptors, and that luminal adenosine content is itself regulated by luminal pH. Altogether, our observations illustrate mechanisms by which CCs are activated by pH sensitive P2X4 receptor and ectonucleotidases, providing a feedback mechanism for the maintenance of luminal pH. These novel mechanisms by which professional proton-secreting cells respond to extracellular cues to modulate their functions, as well as how they communicate with neighbouring cells, might be translatable to other acidifying epithelia.

High‐Quality White Organic Light‐Emitting Diodes Composed of Binary Emitters with Color Rendering Index Exceeding 80 by Utilizing Color Remedy Strategy

AbstractImplementing rigorous standards for high‐quality white organic light‐emitting diodes (WOLEDs) demands further investigation. Herein, a novel and feasible color remedy strategy (CRS) is proposed in WOLEDs composed of binary‐emitters, to arouse the green‐emission, thereby complementing the spectral deficiency in white‐emission. Thus, the color rendering indexes (CRIs) of binary‐emissive WOLEDs can be boosted from 63 to 80 threshold, and the Commission International de I'Eclairage‐(x, y) coordinates are precisely located inside the American National Standard Institute quadrangles, which can rival the WOLEDs integrating ternary or more emitters. Moreover, it is more feasible for CRS‐based binary‐emissive system to tune white‐emission from cool white‐emission (correlated color temperature (CCT) ≈ 5000 K) to eye‐friendly warm white‐emission (CCT ≈ 2000 K). Meanwhile, benefiting from the reduced energy loss and low driving voltage of CRS zone, all of the CRS‐based WOLEDs with diverse CCTs can exceed 20% external quantum efficiency, and the highest approach 25%, as well as the highest power efficiency beyond 60 lm W−1, which is comparable with those reported employing light‐extracting techniques. In addition, it is evident that CRS‐based WOLEDs also exhibit outstanding color stability within the variation of luminance in several orders of magnitude (50–12 000 cd m−2). Thus, this novel CRS provides an innovative pathway to fabricate high‐quality WOLEDs composed of binary emitters.

Neural Network Based Luminance Variation Resistant Remote-Photoplethysmography for Driver’s Heart Rate Monitoring

The driver's physiological status has enormous value to public traffic safety and cannot be ignored nowadays. In addition, heart rate (HR) is one of the most important indicators of human's health status. When detecting the driver's HR, using traditional contact-type devices might bring about the driver's distraction or discomfort. On the contrary, the remote photoplethysmography (rPPG) technique is a better way to monitor a driver's HR in vehicle applications simply by using a web-camera without interfering the driver. Most of the rPPG studies intended to reduce the interference caused by facial motion or luminance changes in the indoor or controlled scenario, but there are relatively fewer discussions on outdoor scenarios. Consequently, the purpose of this paper is to enhance the rPPG technique to make it suitable for the outdoor driving scenarios and for monitoring the driver's HR in different weather conditions, including daytime and nighttime. We first utilize artificial neural network (ANN) and train multiple personalized ANN models for each driver. For predicting the drivers' HR beat more precisely, we propose the approach, adaptive neural network model selection (ANNMS), which adaptively selects a personalized ANN model based on different noise conditions. Our algorithm eliminates the effect of noises caused by the variations of facial luminance in eight outdoor driving scenarios. The proposed driver's HR beat monitoring system has been evaluated against the state-of-the-art rPPG techniques that are Chrominance signal-based (CHRO) and k-nearest neighbors-based (kNN) algorithms. Compared with the CHRO and kNN algorithms, the ANNMS reduces the mean absolute error from 14.71 bpm (CHRO) and 9.91 (kNN) to 4.51 bpm (ANNMS) and enhances the success-rate-10, the probability in which the absolute error is below 10 bpm, from 44.1% (CHRO) and 56.3% (kNN) to 91.5% (ANNMS).

基于LED显示屏基色亮度变化的白场亮色度偏差分析

基于LED显示屏基色亮度变化的白场亮色度偏差分析

A Highly Power-Efficient Single-Inductor Bipolar-Output DC–DC Converter Using Hysteretic Skipping Control for OLED-on-Silicon Microdisplays

In this brief, a highly power-efficient single-inductor bipolar-output (SIBO) DC–DC converter is proposed for use as the pixel power supply of organic light-emitting diode-on-silicon microdisplays, which are used in virtual reality and augmented reality applications. The proposed SIBO DC–DC converter regulates its negative output voltage ( ${V_{\mathrm{ ON}}}$ ) using hysteretic skipping to reduce the number of switching operations, resulting in an increase in power efficiency. In addition, it regulates the positive output voltage ( ${V_{\mathrm{ OP}}}$ ) with higher priority than ${V_{\mathrm{ ON}}}$ , thus having little influence on pixel luminance variations. The proposed SIBO DC–DC converter was designed for a maximum load current of 30 mA, a ${V_{\mathrm{ OP}}}$ of 4.80 V, and a ${V_{\mathrm{ ON}}}$ of −2.50 V. It was fabricated using 90-nm standard CMOS process technology with high voltage devices of 8 V. The measurement results show that the ripples of ${V_{\mathrm{ OP}}}$ and ${V_{\mathrm{ ON}}}$ are 17 mV and 50 mV, respectively, at a load current of 20 mA. The measured load regulations of ${V_{\mathrm{ OP}}}$ and ${V_{\mathrm{ ON}}}$ are 0.03 mV/mA and 0.06 mV/mA, respectively. The measured line regulations of ${V_{\mathrm{ OP}}}$ and ${V_{\mathrm{ ON}}}$ are 1.25 mV/V and 2.50 mV/V, respectively. In addition, the measured maximum power efficiency is 90.1%.

Evaluation of Antifingerprint Properties of Plastic Surfaces Used in Automotive Components

The antifingerprint properties of a range of surfaces produced with different technologies (in-mould decoration, in-mould labeling, and painted) were objectively evaluated by depositing on them in standard conditions an artificial fingerprint for direct determination of its visibility. The artificial fingerprint behaves similarly to the real human fingerprints. A classification method is then proposed to classify surfaces on the base of antifingerprint properties by measuring the roughness profile (Ra) and calculating the % variation of gloss (GU 20 and 60°), haze, luminance (L), and diffuse reflectance (R) values after fingerprint deposition. This approach provides an objective and quantitative test method to determine visual antifingerprint properties of coated surfaces, instead of the “easy-to-clean” properties commonly evaluated. The data acquired provides a design guideline for fabricating visually fingerprint-free surfaces by controlling roughness, texture, color, and transparency of surfaces, with the aim of optically masking fingerprints.

Luminance gradients and non-gradients as a cue for distinguishing reflectance and illumination in achromatic images: A computational approach

The brain analyses the visual world through the luminance patterns that reach the retina. Formally, luminance (as measured by the retina) is the product of illumination and reflectance. Whereas illumination is highly variable, reflectance is a physical property that characterizes each object surface. Due to memory constraints, it seems plausible that the visual system suppresses illumination patterns before object recognition takes place. Since many combinations of reflectance and illumination can give rise to identical luminance values, finding the correct reflectance value of a surface is an ill-posed problem, and it is still an open question how it is solved by the brain. Here we propose a computational approach that first learns filter kernels (“receptive fields”) for slow and fast variations in luminance, respectively, from achromatic real-world images. Distinguishing between luminance gradients (slow variations) and non-gradients (fast variations) could serve to constrain the mentioned ill-posed problem. The second stage of our approach successfully segregates luminance gradients and non-gradients from real-world images. Our approach furthermore predicts that visual illusions that contain luminance gradients (such as Adelson’s checker-shadow display or grating induction) may occur as a consequence of this segregation process.

Consumption of non-digestible oligosaccharides elevates colonic alkaline phosphatase activity by up-regulating the expression of IAP-I, with increased mucins and microbial fermentation in rats fed a high-fat diet.

We have recently reported that soluble dietary fibre, glucomannan, increased colonic alkaline phosphatase (ALP) activity and the gene expression without affecting the small-intestinal activity and that colonic ALP was correlated with gut mucins (index of intestinal barrier function). We speculated that dietary fermentable carbohydrates including oligosaccharides commonly elevate colonic ALP and gene expression as well as increase mucin secretion and microbial fermentation. To test this hypothesis, male Sprague-Dawley rats were fed a diet containing 30 % lard with or without 4 % fructo-oligosaccharides (FOS), galacto-oligosaccharides (GOS), raffinose (RAF) and lactulose (LAC), which are non-digestible oligosaccharides or isomalto-oligosaccharides (IMOS; some digestible oligosaccharides) for 2 weeks. Colon ALP activity, the gene expression and gut luminal variables including mucins, organic acids and microbiota were measured. Colonic ALP was significantly elevated in the FOS, RAF and LAC groups, and a similar trend was observed in the GOS group. Colonic expression of intestinal alkaline phosphatase (IAP -I), an ALP gene, was significantly elevated in the FOS, GOS and RAF groups and tended to be increased in the LAC group. Dietary FOS, GOS, RAF and LAC significantly elevated faecal mucins, caecal n-butyrate and faecal ratio of Bifidobacterium spp. Dietary IMOS had no effect on colonic ALP, mucins, organic acids and microbiota. Colon ALP was correlated with mucins, caecal n-butyrate and faecal Bifidobacterium spp. This study demonstrated that non-digestible and fermentable oligosaccharides commonly elevate colonic ALP activity and the expression of IAP-I, with increasing mucins and microbial fermentation, which might be important for protection of gut epithelial homoeostasis.

Seamless Multi-Projection Revisited.

This paper introduces a novel photometric compensation technique for inter-projector luminance and chrominance variations. Although it sounds as a classical technical issue, to the best of our knowledge there is no existing solution to alleviate the spatial non-uniformity among strongly heterogeneous projectors at perceptually acceptable quality. Primary goal of our method is increasing the perceived seamlessness of the projection system by automatically generating an improved and consistent visual quality. It builds upon the existing research of multi-projection systems, but instead of working with perceptually non-uniform color spaces such as CIEXYZ, the overall computation is carried out using the RLab [10, pp. 243-254] color appearance model which models the color processing in an adaptive, perceptual manner. Besides, we propose an adaptive color gamut acquisition, spatially varying gamut mapping, and optimization framework for edge blending. The paper describes the overall workflow and detailed algorithm of each component, followed by an evaluation validating the proposed method. The experimental results both qualitatively and quantitatively show the proposed method significant improved the visual quality of projected results of a multi-projection display with projectors with severely heterogeneous color processing.

Fabrication Process and Performance Analysis of CSP LED Filaments with a Stacked Package Design

This article presents a chip-scale package (CSP) based filament light-emitting diodes (LEDs) with a stacked-type structure and a segmented-type luminescence design for higher luminous efficiency and better electrical stability. The innovation strategy improves the luminous efficiency by 7.69% and 18.97% than the traditional dispensing packaged LED filament when the current is at 30 mA and 210 mA, respectively, and reduces the use of red phosphors and green phosphors by 66.7% and 26.2%, respectively. With the increase of the current, the luminous efficiency variations of the stacked-packaged filament are lower than that of the traditional dispensing packaged filament. Moreover, the color temperature of the filament is no longer determined by the calculation of the ratio of various phosphors. The stacked structure and the segmented design can help us to adjust the specified color temperature quickly by changing the proportion and position of the blue chips and the red CSP LEDs.

Two optimized models of life prediction based on luminance degradation for VFD under a conventional life test

AbstractFocusing on improving the accuracy of existing life prediction models for optoelectronic products, the three‐parameter Weibull right approximation method (TPWRAM) was employed to substitute exponential function based on the least square method in the analysis and two‐staged methods. Two optimized models were established (Model I and Model II), based on maximum likelihood estimation and the Monte Carlo method, respectively. One group of conventional life tests (CLTs) of vacuum fluorescent display (VFD) were conducted to collect luminance degradation data for each sample, and the two optimized models were applied to achieve VFD life prediction and obtain mean time to failure, median life, and confidence intervals. The results indicate that the CLT test design is correct and feasible, the amount of data on luminance degradation is large, and the test data selection method is reasonable. Model I and Model II optimized by TPWRAM both reflect the VFD luminance variation law well, and the predicted life approaches VFD service life from user feedback, proving that the two models are precise, and thus, can provide technical references for researchers and engineers regarding aspects of life prediction.

Evaluation of a hybrid photo-radiometer sky model compared with the Perez sky model

Daylight simulation results greatly rely on the accuracy of sky models. When generic CIE sky and Perez all-weather sky simulate daylighting scenes they simplify cloud distributions. The lack of cloud distributions and subtle luminance variations causes simulation result deviations. High Dynamic Range (HDR) image techniques provide a method of generating accurate and actual skies. This paper explores the accuracy of a horizontal hybrid phadiometer (HPR) sky model, which combines modeled physical descriptions of the sun and HDR sky images. The aim was to build on and enrich the findings of a previous study (Humann and McNeil, 2017).In this study, the HDR images within four office spaces were taken. Simultaneously, global horizontal illuminance and HDR sky images were recorded outside. Simulated luminance maps were generated under both the HPR and Perez skies. Daylight Glare Probability and vertical eye illuminance (Ev) were calculated from 112 groups of luminance maps. The simulated Ev under HPR and Perez skies presented relative RMSE of 21.3% and 23.7%, respectively. The frequencies of accurate glare prediction under HPR and Perez skies were 95.5% and 93.9%, respectively. The results indicated that both the horizontal HPR sky and the Perez sky simulate equally accurate luminance maps.