Number Of Light Sources Research Articles

A Model for Evaluating the Visual Perception of an Arbitrary Distribution of Luminance in Indoor Lighting Installations

How to assess what kind of feeling the lighting scene causes? A new level of computer graphics visualization makes it possible to think about real image through synthetic images from one hand, and from other hand, today the HDRi method allows fixing luminance with an accuracy of up to 10 % in a wide range. Therefore, assessing the lighting quality of designed and existing lighting installations in terms of luminance reaches a new level. It brings the creating of psychophysical model of lighting quality assessment through photometric quantities closer. The structure of the model can be represented in two parts: the calculation equation and the psychophysical scale. This work considers the issue of choosing categories of the psychophysical scale, the method of creating of luminance maps for scene with an arbitrary spatial angle luminance distribution, and the method for evaluating scenes using a new gradient criterion Q based on these maps. An analysis of HDRi images of workplaces based on the experimental setup and scenes in a cafe showed that the Q criterion depends on the type of scene and on the number of light sources in the field of view. One could suggest that it is impossible to create one single psychophysical scale for the Q criterion. However, one can use this new criterion to evaluate the same scenes with different lighting options or similar scenes in terms of spatial luminance distribution and glare. Despite of the luminance map values have an error of about 30 % the using HDRi image of scene allows to calculate Q criterion with an accuracy of about 10 %.

Shadow Effect of Human Obstacles on Indoor Visible Light Communication System with Multiple Light Sources

When the direct visible-light channel is affected by people walking or other obstacles, the shadow effect formed in the receiver space affects communication performance and can even lead to communication interruption. In this paper, two numerical methods for calculating the shadow area of the human body were proposed for an indoor multi-light communication system. The influence of shadows on system performance was analyzed using the mean square errors of illuminance and signal-to-noise ratio, as well as the interrupt probability, as parameters. The results showed that shadows had a great influence on the performance of the visible-light communication system. When the number of light sources was fixed, the shadow effect could be effectively reduced by optimizing the layout of the light sources. These research results can provide a theoretical basis for improving the stability of visible-light communication systems.

SHAPE FROM POLARIZATION FOR FEATURELESS AND SPECULAR OBJECTS

Abstract. Objects with textureless and specular surfaces are commonplace in manmade environments. Their reconstruction challenges optical 3-D metrology methods typically yielding incomplete and noisy results. Existing solutions, including structured light, shape from shading, and learning-based specular removal methods, place a high demand on projection patterns, the number of light sources and cameras, or training data. While requiring elaborate setups, these solutions are not general enough, and their success in handling these surfaces is only partial. To address this reconstruction challenge, we study in this paper the application of shape from polarization for the 3-D reconstruction of textureless objects. Using a single view and a known light source, polarization-based constraints can be expressed as a set of linear equations for the unknown depth. We then estimate depth directly as an optimization problem constrained by the linear polarization equations. Results demonstrate complete and accurate 3-D reconstructions of typical glossy featureless objects, suggesting that shape from polarization is a valuable strategy for generating dense 3-D surface models.

N-White Balancing: White Balancing for Multiple Illuminants Including Non-Uniform Illumination

In this paper, we propose a novel white balance adjustment for multi-illuminant scenes, called “N-white balancing,” in which N source white points are mapped into a ground truth one. Most white balance adjustments focus on adjusting single-illuminant scenes. Several state-of-the-art methods for adjusting multi-illuminant scenes have been proposed, but they need to know the number of segments or the number of light sources in advance. Multi-color balance adjustments have been investigated to improve the performance of white balancing, but they also suffer from color distortion due to the rank deficiency problem. In contrast, the proposed method, N-white balancing, can correct multi-illuminant scenes even when we do not know the exact number of segments or light sources in a scene. In an experiment, the proposed method was demonstrated to outperform state-of-the-art methods under various illumination conditions such as single and multiple illuminants including non-uniform light sources.

Light Source Layout Optimization Strategy Based on Improved Artificial Bee Colony Algorithm

In order to optimize the indoor lighting effect and reduce the energy consumption of indoor lighting, the light source layout of conventional rooms and special rooms is studied in this paper. Firstly, the indoor space lighting model is analyzed, and the expressions of light source output and illumination on the target plane are derived. Secondly, in order to improve the search ability of the algorithm in specific areas, combined with the artificial bee colony algorithm, an improved artificial bee colony algorithm suitable for indoor lighting optimization is proposed. Using the average square difference of the illuminance of the target plane as the adaptation function, a penalty function is introduced, and the minimum circle surrounding strategy is used to search the specific location of the light source. Finally, the obtained layout is fitted by engineering standardization, and the indoor light source layout is obtained. Through the simulation of illuminance effect in conventional room and irregular room, it is proved that the proposed method can effectively improve the lighting effect and reduce the energy consumption of indoor lighting under the same number of light sources and the same illuminance index.

Characteristics of light pollution – A case study of Warsaw (Poland) and Fukuoka (Japan)

Artificial light has been present in human life for decades but our knowledge of its effects is still insufficient. Lighting lets us be active longer, gives us a sense of security and provides aesthetic experiences. Despite all of these advantages, in urban areas artificial light also has a negative effects on the environment and human life. Although light pollution is one of the most common forms of anthropogenic environmental change, this phenomenon remains insufficiently investigated. The present work thus focuses on night sky brightness and artificial factors impacting the level of the phenomenon using Warsaw (Poland) and Fukuoka (Japan) as an example. The basis of the study is the new World Atlas of Artificial Night Sky Brightness. Moreover, we used image data from the Visible Infrared Imaging Radiometer Suite Day/Night Band and data from field research to analyse the primary artificial light characteristics in the two cities: illumination, colour temperature, peak wavelength, dominant wavelength, stimulation of photoreceptors, design of lighting fixtures and radiance. The results indicate that Warsaw (area: 517.2 km2; population: 1 777 972) is characterized by higher light pollution than Fukuoka (area: 343.5 km2; population: 1 554 229). Skyglow is primarily influenced by the number of light sources; however, local differentiation of the phenomenon depends on the spectral characteristics and design of lighting fixtures. Moreover, environmental features may affect light pollution through scattering, reflection and absorption. Outdoor lighting in Warsaw was characterized by a higher value of light illumination and greater stimulation of photoreceptors sensitive to long and medium waves. However, the lighting infrastructure in Fukuoka was also unsuitable, as it was characterised by high values of colour temperature and stimulation of photoreceptors sensitive to short waves and ganglion cells, which may be detrimental to the human body.

Remotely Pumped All-Optical Wavelength Conversion for WDM-PON-Based Access-Metro Convergence

Access-metro convergence networks (AMCN) have been proposed as a future optical communication network to realize flexible and dynamic bandwidth allocation. An AMCN requires transceivers with different wavelengths for the optical network units (ONUs). This causes an increase in production costs. Although an all-optical wavelength converter (AOWC) mitigates this issue, the AOWC increases the installation cost because it consists of many expensive optical devices. We propose the use of a remotely pumped AOWC (RP-AOWC) with an AMCN. The proposed technique can reduce the number of pump light sources in the AOWC. This paper demonstrates this reduction in the number of light sources and the feasibility of wavelength conversion using pump light propagation. We calculate the reduction in the number of pump sources and the number of transceiver types caused by the use of RP-AOWC and experiment with the wavelength conversion using pump light propagation.

The Interplay Between Block Design Theory and Channel Estimation in Visible Light System

The problem of channel gain estimation in visible light communications and positioning is considered in this article. Pilot sequences are designed for simultaneously estimating the channel gains of multiple transmitters in a light system and satisfying the average and maximum transmit power constraint due to illumination purpose. This article illustrates how to design the optimal pilot sequences that minimise the noise variance experienced by a receiver although the optimisation problem is non-convex. Lower bounds on the noise variance are derived for systems with ambient light and systems without ambient light. These bounds reveal the relationship between noise variance, the average transmit power, the maximum transmit power, the number of light sources and pilot length. The necessary and sufficient conditions for the bounds to hold with equality are derived. These conditions establish a bridge between block design theory and channel estimation in visible light systems. Optimal pilot designs which achieve the lower bounds on noise variance can be obtained from balanced block designs and pairwise balanced designs. This article also shows how to optimise the average transmit power of a pilot design for minimising noise variance.

室内可见光通信系统的光源布局优化及性能分析

In the indoor visible light communication (VLC) system based on white light-emitting diode (LED), considering the primary reflection of the wall, the layout schemes of different LED topology are studied. By adjusting the topological distribution, the square array combined with the circular ring layout model is proposed to reduce the power consumption of system, and the dynamic range compressions of illuminance and signal-to-noise ratio (SNR) of the receiving plane are realized by power distribution under the indoor lighting requirements. The illuminance distribution, received power distribution, SNR distribution and bit error rate (BER) performance of the square array combined with the circular ring layout model based on power distribution are simulated and analyzed. The simulation results show that the number of light sources used in the square array combined with the ring layout is reduced by 48 compared with the traditional square array layout, but the performance is still improved. At the same time, the relationships between bandwidth, BER, distance and SNR of indoor VLC link system are given, which can provide reference for users to build VLC links. © 2019, Chinese Lasers Press. All right reserved.

Is Seeing Still Believing: Factors That Allow Humans and Machines to Discriminate Between Real and Generated Images

The growing photorealistic capabilities of 3D animation and computer-generated imagery (CGI) poses potential issues for broadcasters, regulators, governments, and viewers. What happens if a news story is broadcast, or available on a website, that is CGI or a combination of CGI and camera-acquired images? There are already instances of video where there is polarized debate as to the degree of CGI present in the published content, a prime example being the Islamic State of Iraq and Syria (ISIS) video of the burning of a person. An analysis of the artefacts seen in the video that gave rise to the truthfulness debate is presented. The factors that humans use to discriminate or to evaluate the realness of photographs include shadow softness, surface smoothness, scene complexity and composition, and the number of light sources. Initial studies showed a human ability to discriminate; however, recent studies have shown that the ability to discriminate is getting more difficult, although with training the ability improves. Computer Vision research has evaluated image features and descriptors that discriminate between photographs and CGI. No such studies with quantitative data or experimental methodologies seem to exist for evaluating the CGI moving image by humans or computers. Possible temporal assessment factors for human discrimination (motion parameters), for computer vision (optical flow), and for artificial intelligence (semantic scene analysis) are presented.

Multiplexing technique for quasi-distributed sensors arrays in polymer optical fiber intensity variation-based sensors

This paper presents a multiplexing technique for polymer optical fiber (POF) intensity variation-based sensors. The technique relies on the side-coupling between the light source and the POF lateral section. Thus, each sensor has its own light source which has its activation as well as its signal acquisition (made with two photodetectors, one at each end of the POF) controlled by a microcontroller. With this technique, a matrix with the number of columns equal to the number of photodetectors multiplied by the number of light sources (or sensors) is obtained. This enables the decoupling of the response of each sensor. The presented analytical approach shows a tradeoff between the number of sensors and their sensitivities (considering the dynamic range of each sensor). In addition, experimental results show the feasibility of the technique to measure angles in a 3°-of-freedom (DOF) systems with errors as low as 3°. Furthermore, the proposed approach was also tested in multi-parameter applications, where temperature, angle and force were estimated with errors up to 5% with an array with 3 POF sensors. The results presented in this paper can pave the way for novel applications of quasi-distributed sensors with intensity variation-based sensors both in multi-DOF systems and in multi-parameter applications with the additional advantages of lower cost than fiber Bragg gratings-based systems and lower spatial resolution than distributed sensors.

Gesture Recognition Using Ambient Light

There is a growing interest in the scientific community to develop techniques for humans to communicate with the computing that is embedding into our environments. Researchers are already exploring ubiquitous modalities, such as radio frequency signals, to develop gesture recognition systems. In this paper, we explore another such modality, namely ambient light, and develop LiGest, an ambient light based gesture recognition system. The key property of LiGest is that it is agnostic to lighting conditions, position and orientation of user, and who performs the gestures. The general idea behind LiGest is that when a user performs different gestures, the shadows of the user move in unique patterns. LiGest first learns these patterns using training samples and then recognizes unknown samples by matching them with the learnt patterns. To capture these patterns, LiGest uses a grid of light sensors deployed on floor. While the general idea behind LiGest seems straightforward, it is actually very challenging to put it into practice because the intensity, size, and number of shadows of a user are not fixed and depend highly on the position and orientation of a user as well as on the intensity, position, and number of light sources. We developed a prototype of LiGest using commercially available light sensors and extensively evaluated it with the help of 20 volunteers. Our results show that LiGest achieves an average accuracy of 96.36% across all volunteers.

ElasticFusion: Real-time dense SLAM and light source estimation

We present a novel approach to real-time dense visual simultaneous localisation and mapping. Our system is capable of capturing comprehensive dense globally consistent surfel-based maps of room scale environments and beyond explored using an RGB-D camera in an incremental online fashion, without pose graph optimization or any post-processing steps. This is accomplished by using dense frame-to-model camera tracking and windowed surfel-based fusion coupled with frequent model refinement through non-rigid surface deformations. Our approach applies local model-to-model surface loop closure optimizations as often as possible to stay close to the mode of the map distribution, while utilizing global loop closure to recover from arbitrary drift and maintain global consistency. In the spirit of improving map quality as well as tracking accuracy and robustness, we furthermore explore a novel approach to real-time discrete light source detection. This technique is capable of detecting numerous light sources in indoor environments in real-time as a user handheld camera explores the scene. Absolutely no prior information about the scene or number of light sources is required. By making a small set of simple assumptions about the appearance properties of the scene our method can incrementally estimate both the quantity and location of multiple light sources in the environment in an online fashion. Our results demonstrate that our technique functions well in many different environments and lighting configurations. We show that this enables (a) more realistic augmented reality rendering; (b) a richer understanding of the scene beyond pure geometry and; (c) more accurate and robust photometric tracking.

Inverse lighting design using a coverage optimization strategy

Lighting design is an essential process in computer cinematography, games, architectural design and various other applications for correctly illuminating or highlighting parts of a scene and enhancing storytelling. When targeting specific illumination goals and constraints, this process can be tedious and counter-intuitive even for experienced users and thus automatic, goal-driven methods have emerged for the estimation of a lighting configuration to match the desired result. We present a general automatic approach to such an inverse lighting design problem, where the number of light sources along with their position and emittance are computed given a set of user-specified lighting goals. To this end, we employ a special hierarchical light clustering that operates in the lighting goal coverage domain and overcomes limitations of previous approaches in environments with high occlusion or structural complexity. Our approach is independent of the underlying light transport model and can quickly converge to usable solutions. We validate our results and provide comparative evaluation with the current state of the art.

Olbers’ Paradox Resolved for the Infinite Nonexpanding Universe

The conventional argument holds that the night sky is dark because the universe is expanding and the lifespan of stars is limited. Expansion weakens the light and star deaths reduce the number of light sources. Ultimately there will be no new formation of stars. However, the conventional resolution of Olbers’ Paradox is no longer tenable. It turns out that the Universe is not expanding, the Universe is not evolving, and there is no restriction on the number of stars — the process of star formation is perpetual. With the recent publication of two revolutionary papers, one describing a simple cosmic redshift mech-anism wherein wavelength elongation occurs in both expanding space and contracting space and the other detailing the resolution of what is undisputedly the most intractable anomaly in astronomy and astrophysics, the true nature of the Universe has been revealed —our world is a steady state cellular cosmos. The real Universe does not expand; furthermore, the numbers of light sources are infinite and their average spacing density never changes (since they are perpetually being replaced). Clearly, neither of the two conventional arguments will work. The following is a new two-part resolution of the night-sky-darkness question —a natural resolution that exploits the new cosmic redshift mechanism, known as the velocity-differential shift, and a photon extinction-probability mechanism.

Dynamic mesh-based analysis of dynamic irradiance characteristics of solar simulator

The unsteady motion of a solar simulator was simulated using dynamic mesh technology in Fluent software. The dynamic irradiation characteristics of the simulator were studied under various conditions. Mesh updates were achieved using a dynamic layering method, and the periodic lifting motion of the simulator was defined using user-defined functions (UDF). Detailed dynamic irradiance characteristics were obtained for comparison with experimental results. The results showed that the simulator height and the number of light sources used were the main factors that affected the irradiance. The irradiance has a linear relationship with the simulator height, which means that the irradiance non-uniformity decreases with decreasing solar height; in addition, the sum of the irradiances under the various operating conditions matches the superposition of the irradiance. The dynamic irradiation numerical results are consistent with the experimental results at typical points, which verifies the reliability of the moving mesh numerical model. The validated model can be used to study various simulator conditions and provides forecast data for diurnal variation simulation of solar radiation.

Research on the light emitting diode array launching performance for indoor visible light communication

A kind of illumination calculation of array antenna composed of light emitting diode (LED) source based on Lambert radiation model is proposed. This paper puts emphasis on the optimal design for the transmitting antenna of indoor visible light communication. And it also analyzes the influence of the forms of the spatial distribution of the light source, the distance between light sources, and the angle between the center beam of light source and optical axis of the system, as well as the layer spacing of space distribution on illumination uniformity. A circular array antenna is superior to a rectangular array antenna containing the same number of light sources in illumination uniformity and stability of signal transmission, which may increase by 10%. As the distance between light sources and the angle between the center beams of light sources and optical axis keep increasing, the illumination uniformity of array antenna composed of LED source increases first and then starts to drop. As a result, there exist the optimal values in the distance and the angle respectively. Illumination uniformity increases with the decrease of the distance of space distribution. The optimal value of design parameter of transmitting antenna array in a common room has been given, therefore, it optimizes launch performance, saves as much as 13% the number of light source and reduces the cost. These studies for the design of the transmitting antenna system provide a theoretical basis and practical values.

Robust moving shadow detection with hierarchical mixture of MLP experts

Detection and elimination of the shadows of moving objects in video sequences have been one of the major challenges in tracking applications. Since moving shadows cannot be removed from foreground by motion-based background subtraction methods, they lead to confusion and error in moving object tracking. In this paper, a novel classification method based on hierarchical mixture of experts learning for detecting shadows from foreground is proposed. A hierarchical mixture of MLP experts method (HMME) with semi-supervised teacher-directed learning (SSP-HMME) is used. It contains a two-level mixture of experts (ME) system. The main superiority of this method is that it is more robust than state-of-the-art methods in all types of indoor and outdoor environments. The robustness is against the number of light sources, illumination conditions, surface orientations, object sizes, etc., and it is estimated using accuracy rates. The video set has been collected from 7 different datasets. The results of experiments in outdoor and indoor environments show the validity of the method in the improvement on the accuracy of both detection and discrimination rate for moving shadows in video sequences. The results of the experiments show the accuracy rate of 89 % in average in different indoor and outdoor environmental conditions that is about 6 % better than current state-of-the-art methods.

Illumination Insensitive Face Recognition Using Gradientfaces

The performance of most existing face recognition methods is highly sensitive to illumination variation. It will be seriously degraded if the training/testing faces under variable lighting. Thus, illumination variation is one of the most significant factor affecting the performance of face recognition and has received much attention in recent years. In this paper we propose a novel method called gradientface for face recognition under varying illumination. When we rarely know the strength, direction or number of light sources. The proposed method has the ability to extract illumination insensitive measure, which is then used for face recognition. The merits of this method is that neither does it require any lighting assumption nor does it need any training images. Gradientface method reaches very high recognition rate of 98.96% in the test on yele B face database. Further more the experimental results on Yale database validate that gradient faces is also insensitive to image noise and object artifacts such as facia;l expression.

Removal of non-uniform complex and compound shadows from textured surfaces using adaptive directional smoothing and the thin plate model

In this study, the authors propose a novel algorithm for removing complex shadows from textured surfaces within a single image. Previous shadow removal methods have attempted to solve this problem under a range of criteria, such as the type and number of light sources and shadow structure. Some methods require that the shadow umbra and penumbra be well defined. They have been shown to work best when the umbra is relatively large and when the penumbra is of a limited size and shape. However, these methods can fail if the shadow shape or form diverges from the norm. Many methods also require user intervention to locate whole or parts of the shadow. The authors propose a flexible shadow removal model which is capable of functioning without these limiting assumptions, or the need for user intervention. It is also capable of dealing with shadows cast on a wide range of textured surfaces. It uses a directional differential filter along with directional smoothing to find the shadow and a thin plate reconstruction model to remove shadows from an image surface. Results have shown that the proposed algorithm generates high-quality shadow-free images over a range of scenarios, such as multiple light sources, occlusions and textures.