Using shadows in finding surface orientations

Most existing face recognition algorithms work well for controlled images but are quite susceptible to changes in illumination and pose. This has led to the rise of analysis-by-synthesis approaches due to their inherent potential to handle these external factors. Though these approaches work quite well, most of them assume that the face is illuminated by a single light source which is usually not true in realistic conditions. In this paper, we propose an algorithm to recognize faces illuminated by arbitrarily placed, multiple light sources. The algorithm does not need to know the number of light sources and works extremely well even while recognizing faces illuminated by different number of light sources. Results using this algorithm are reported on multiple-illumination datasets generated from PIE by T. Sim, et al. (2003) and Yale Face Database B by W. Zhao, et al. (2003). We also highlight the importance of the hard non-linearity in the Lambert's law which is often ignored, probably to linearize the estimation process

Several techniques have been developed for recovering reflectance properties of real surfaces under unknown illumination conditions. However, in most cases, those techniques assume that the light sources are located at infinity, which cannot be applied to, for example, photometric modelling of indoor environments. We propose two methods to estimate the surface reflectance property of an object, as well as the position of a light source from a single image without the distant illumination assumption. Given a color image of an object with specular reflection as an input, the first method estimates the light source position by fitting to the Lambertian diffuse component, while separating the specular and diffuse components by using an iterative relaxation scheme. Moreover, we extend the above method by using a single specular image as an input, thus removing its constraints on the diffuse reflectance property and the number of light sources. This method simultaneously recovers the reflectance properties and the light source positions by optimizing the linearity of a log-transformed Torrance-Sparrow model. By estimating the object's reflectance property and the light source position, we can freely generate synthetic images of the target object under arbitrary source directions and source-surface distances.

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.

Two‐stage polymerizing‐then‐degrading networks are achieved by exposure to a single near UV light source, by sequentially performing thiol–ene photopolymerization and radical‐mediated thioaminal scission. To understand the mechanisms involved, synthesis of model thioaminal small molecules shows photo‐activated thioaminal scission produces thioamide moieties, identifiable by distinct NMR singlets at 3.29 and 3.26 ppm and a Fourier Transform IR (FTIR) peak ≈1530 cm−1. The scission process is proposed to occur via ß‐scission of the carbon next to the sulfur atom and is found to be influenced by thiol substitution on the thioaminal, leading to scission conversion increasing from 5 ± 1 to 39 ± 3% and scission time decreasing from 6 to 2 min as the thiols become progressively more substituted. Thioaminal scission occurs semi‐orthogonally with radical‐mediated thiol–ene reactions; the thiol–ene reaction achieves near quantitative yield within the first 0.5 min while thioaminal scission requires a further 5–15 min. This semi‐orthogonality is exploited to create two‐stage polymerizing‐then‐degrading networks, with both regimes dependent on total light dose from a single light source and the transition occurring ≈2 J cm−2 under these exposure and polymerization conditions. This work establishes thioaminals as a new photo‐mediated scission chemistry and a means to create multi‐stage, light‐activated networks.

For photometric stereo in capsule endoscopy, calibration of light source is crucial for improving the precision of surface normal estimation. Therefore, this paper presents an improved planar-mirror-based light source position calibration method: from captured images of light source and detected poses of planar mirror, light paths are retraced from camera to light source, and position of light source is triangulated with least square method. The contribution of this paper is that a refraction model of the planar mirror is employed in the retracement of light paths, thus the bias of light paths caused by refraction can be compensated and the position of light source can be estimated more precisely. The results of simulation and experiment show that the proposed method provides higher calibration accuracy than the current planar mirror-based calibration method and can improve the precision of subsequent photometric stereo-based 3D reconstruction.

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.

According to commonly consented theories, the minimum hardware requirement for gaze tracker is one camera and two light sources to realize gaze estimation with free head movements [1]. However, in some scenarios such as eye tracking on mobile devices, it is preferable to use less components, especially light sources. We propose a gaze estimation method with one camera and one light source. A virtual light is introduced, which is geometrically placed symmetrically to the real light source with respect to the camera, and generates a virtual glint in the acquired image. We estimate the virtual glint by exploiting the relationship between the distance between two pupils and two glints in the captured image, and estimate the gaze with polynomial regression assuming two light sources are available. A new normalization factor for regression method is verified, which turns out to be practical for one-glint system. The performance is proved to be acceptable, while degradation is noticed compared to system with two actual light sources.

In this paper, we consider the problem of estimating the 3D position and intensity of multiple light sources without using any light probe or user interaction. The proposed approach is twofold and relies on RGB-D data acquired with a low cost 3D sensor. First, we separate albedo/texture and illumination using lightness ratios between pairs of points with the same reflectance property but subject to different lighting conditions. Our selection algorithm is robust in presence of challenging textured surfaces. Then, estimated illumination ratios are integrated, at each frame, within an iterative process to recover position and intensity of light sources responsible of cast shadows. Estimated lighting characteristics are finally used to achieve realistic Augmented Reality (AR).

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.

This paper focused on the light source optimization for visual inspection of piston surface defects. A novel structured lighting system was developed to overcome the difficulties in the well-qualified imaging of tiny and random defects on the cylindrical smooth surface of components such as pistons. A polarized light-filtering based method was proposed to enhance the defect image contrast, enlarge the detection range, and suppress the noise of flawless area. It was both experimentally proven and theoretically proven effective by mathematical modeling of light intensity loss during light propagation. To analyze the influence of the pose and position of light sources on defect imaging quality, the system model for camera, light source, and workpiece was established, and the structure parameters of the lighting system were optimized to improve the brightness uniformity over the entire inspection region and lighting efficiency. Moreover, a soft lighting method was introduced as a subsidiary means of removing the surface noise at two ends of a piston. This method was found to be more effective compared with conventional software filtering algorithm. Finally, a case was examined. The defects on the automotive brake master piston surface were captured using the optimized light source system. A random sampling experiment with 600 specimens revealed that the false-positive rate was about 2.3%, and with no leak detection. The findings have been applied in the production, and it is expected to be referred in inspecting defects on other smooth cylindrical surfaces.

In this paper we describe an efficient approach to add shadows to volumetric scenes. The light emitted by the lightsource is properly attenuated by the intervening volumetric structures before it is reflected towards the eye. Both parallel and perspective lightsources can be efficiently and accurately modeled.We use a two-stage splatting approach. In the first stage, a light volume is constructed in O(N3) time, which is about the same time it takes to render a regular image. This light volume stores the volumetric attenuated light arriving at each grid voxel and only needs to be recomputed if the light source is moved. If only diffuse shading is required, then the contribution of any number of lightsources can be stored in the same space. The second stage is formed by the usual rendering pipeline. The only difference is that the light contributions are interpolated from the light volume, instead of using the constant light source intensity. Once the light volume is computed, the actual rendering is only marginally more expensive than in the unshadowed case. The rendered images, however, convey three-dimensional relationships much better and look considerably more realistic, which is clearly needed if volume graphics is to become a mainstream technology.

Traditional physical layer security (PLS) schemes for multi-user visible light communication (MuVLC) are designed with multiple light sources, rendering them inapplicable to MuVLC with single light source. To address this limitation, we propose an innovative relay-aided PLS scheme based on cooperative jamming for MuVLC with single light source. First, we randomly select parts of relays for cooperative jamming, modeling their locations as a Poisson point process (PPP). Then, a jamming signal introduced through these selected relays significantly decreases the signal-to-interference-plus-noise-ratio of the randomly located eavesdroppers, thereby increasing the security capacity. By modeling the eavesdropper locations as another independent PPP, we analyze the security performance by deriving closed-form expressions for the cumulative distribution function of security capacity, security outage probability, its lower and upper bounds, and ergodic security capacity. These theoretical expressions are verified via Monte Carlo simulations. Numerical results show that our scheme achieves high-level communication security. Furthermore, increasing relay density, decreasing eavesdropper density, reducing target security capacity, or lowering relay plane height can effectively reduce security outage probability, offering valuable insights for designing secure MuVLC with single light source.

Wirelessly powered ultraviolet light emitting diodes for photocatalytic oxidation

An understanding of light and its interaction with matter is essential to produce images. As the modeling of light sources, light transport and light reflection improves, it becomes possible to render images with increasing realism. The central motivation behind this thesis is to improve realism in computer graphics images by more accurate local shading models and to assist the user to obtain the desired lighting effects with these more complex models. The first part of the thesis addresses the problem of rendering surfaces illuminated by extended (linear and area) light sources. To compute the light reflected by a surface element in a given direction, one needs to determine the unoccluded regions (shadowing) of each light source and then to compute the light reflection (shading) from each of these regions. Traditionally, point light sources are distributed on the lights to approximate both the shadowing and the shading. Instead, an efficient analytical solution is developed for the shading. Shadowing from extended light sources is a fairly expensive process. To give some insights on the complexity of computing shadows, some properties of shadows and algorithms are presented. To reduce the cost of computing shadows from linear light sources, two acceleration schemes, extended from ray tracing, are introduced and evaluated. The second part of this thesis addresses the problem of achieving a desired shading effect by building up systems of constraints. This approach is called inverse shading. It allows a user to obtain a desired lighting effect by interacting directly with the scene model. An interactive modeling system has been built to study the introduction of rendering issues into the modeling process itself. Two rendering aspects are considered: shading and shadows. By specifying a highlight position and size, the unique direction of a directional light source as well as the surface glossiness are determined. Interactively moving this highlight on the surface redefines the light direction while changing its size redefines the surface glossiness. By manipulating shadow volumes (the volume within which a particular light cannot be completely seen), the light source definition and position can be modified. By assigning colours to various points in a 3D scene, information about the colour of a surface as well as other surface characteristics can be deduced. This relatively new concept of defining the causes by manipulating the effects is expected to have a major impact on the design of future computer graphics modeling systems. It begins a new family of tools for the design of more intuitive user interfaces.

In order to be able to match correctly the track elements produced by a muon in the Tracker and the Muon System of the CMS experiment [1] the mutual alignment precision between the Tracker and the Barrel Muon System must be no worse than 100-400 micrometers depending on the radial distance of the muon chambers from the Tracker. To fulfill this requirement an alignment system had to be designed. This system contains subsystems for determining the positions of the barrel and endcap chambers while a third one connects these two to the Tracker. Since the Barrel muon chambers are embedded into the magnet yoke of the experiment a nonconventional alignment method had to be developed. In this paper we restrict ourselves to the Barrel Alignment System and the calibration methods of its components.