Position Of Light Source Research Articles

Automatic Spatially Varying Illumination Recovery of Indoor Scenes Based on a Single RGB-D Image.

We propose an automatic framework to recover the illumination of indoor scenes based on a single RGB-D image. Unlike previous works, our method can recover spatially varying illumination without using any lighting capturing devices or HDR information. The recovered illumination can produce realistic rendering results. To model the geometry of the visible and invisible parts of scenes corresponding to the input RGB-D image, we assume that all objects shown in the image are located in a box with six faces and build a planar-based geometry model based on the input depth map. We then present a confidence-scoring based strategy to separate the light sources from the highlight areas. The positions of light sources both in and out of the camera's view are calculated based on the classification result and the recovered geometry model. Finally, an iterative procedure is proposed to calculate the colors of light sources and the materials in the scene. In addition, a data-driven method is used to set constraints on the light source intensities. Using the estimated light sources and geometry model, environment maps at different points in the scene are generated that can model the spatial variance of illumination. The experimental results demonstrate the validity and flexibility of our approach.

Nonlinear light-induced vibration behavior of liquid crystal elastomer beam

Recent studies have shown the coupling of optical and mechanical energy in a class of liquid crystal elastomers that contain light-sensitive molecules. As shown experimentally in the literature, these materials can undergo large, reversible elastic deformation under light illumination, and therefore geometric nonlinearity effects can be significant. In this paper, we present a large deflection model for the light-induced bending vibration of a liquid crystal elastomer beam. In this regard, the von Karman's nonlinear strain–displacement relationship is used to account for the large deflection of the beam. The effect of light on the liquid crystal elastomer beam is modeled as an inhomogeneous and time-dependent light-induced contraction strain and the dynamic equations of the beam are derived using the Hamilton's principle. Finite element formulation is developed to analyze the nonlinear dynamic response of the beam under uniform light illuminations. In addition, numerical results are presented and effects of different physical and geometrical parameters, including light intensity, light source position, contraction coefficient, and the thickness of the beam on the vibration characteristics of the beam are investigated. The model developed in this paper can be used to design liquid crystal elastomer based structures such as optically sensors, photo-mechanical energy harvesters, or other reversible opto-mechanically active structures.

Estimating Reflectance Parameters, Light Direction, and Shape From a Single Multispectral Image

This paper presents a novel approach for estimating the light direction, shape, and reflectance parameters from a single multispectral image. We start from a general formulation that hinges in the notion that the light reflected from an object can be deemed to be a linear combination of specular and diffuse reflections. This permits the recovery of the reflection parameters through an iterative optimization scheme, which we render well posed by adopting a novel reparameterization that reduces the number of degrees of freedom in the cost function. With the estimated specular reflectance parameters, we recover the single point light source position from specular highlights by applying two novel constraints, coplanarity and Kullback–Leibler divergence. Then, by integrating the knowledge of light source and diffuse reflectance parameters, we recover shape of the scene from the diffuse component. Our approach is quite general in nature and can be applied to a family of reflectance models that are based on the Fresnel reflection theory. We demonstrate the utility of our method on synthetic and real world imagery. We also compare our results to several alternatives in the literature.

Specular highlight reduction with known surface geometry

The separation of reflection components is an important issue in computer graphics, computer vision, and image processing. This is a highly ill-posed problem since the number of unknowns to solve is much larger than the number of equations. We present a method to reduce the difficulty of this problem by assuming that surface geometry is known. A novel objective function based on robust principal component analysis is proposed to simultaneously separate specularities and estimate the position of light source. We develop an Augmented Lagrangian Multiplier based algorithm to solve the objective function efficiently and effectively. Experimental results on real-world and synthetic data demonstrate the effectiveness of our method.

Point Light Source Position Estimation From RGB-D Images by Learning Surface Attributes.

Light source position (LSP) estimation is a difficult yet an important problem in computer vision. A common approach for estimating the LSP assumes Lambert's law. However, in real-world scenes, Lambert's law does not hold for all different types of surfaces. Instead of assuming all that surfaces follow Lambert's law, our approach classifies image surface segments based on their photometric and geometric surface attributes (i.e. glossy, matte, curved, and so on) and assigns weights to image surface segments based on their suitability for LSP estimation. In addition, we propose the use of the estimated camera pose to globally constrain LSP for RGB-D video sequences. Experiments on Boom and a newly collected RGB-D video data sets show that the state-of-the-art methods are outperformed by the proposed method. The results demonstrate that weighting image surface segments based on their attributes outperform the state-of-the-art methods in which the image surface segments are considered to equally contribute. In particular, by using the proposed surface weighting, the angular error for LSP estimation is reduced from 12.6° to 8.2° and 24.6° to 4.8° for Boom and RGB-D video data sets, respectively. Moreover, using the camera pose to globally constrain LSP provides higher accuracy (4.8°) compared with using single frames (8.5°).

Fuzzy Theory Using in Image Contrast Enhancement Technology

In the process of image acquisition, due to different light source distributions and positions, the problem of overexposure or underexposure will be generated during imaging. Such problems are relatively weak in the detailed information of an image, and the purpose of image enhancement technology is to solve them. Based on the fuzzy problem, this study proposed adaptive parameter image contrast enhancement technology, in order to solve the problems of overexposed and underexposed images. The analysis of the characteristics of the exposure value of an image could determine its adaptive adjustment parameters. The proposed fuzzy decision-making theory was used, and its membership function was applied for re-transformation, in order to achieve image enhancement. The experimental result proved that the fuzzy theory-based adaptive parameter image enhancement algorithm can smoothly optimize image visual quality, without over-enhancing the image, can highlight the detailed information of an image, and can conform to the feeling of human vision.

Quadcopter localization and health monitoring method based on multiple virtual silhouette sensor integration

With the widespread deployment of quadcopters, the flight safety issue attracts increasingly public and academic attentions. This article presents a quadcopter flight regime extraction algorithm for quadcopter localization and health monitoring using imageries captured by general purpose monocular cameras. First, contour information is extracted from quadcopter shadows on the ground. In order to better illustrate the three-dimensional silhouette information contained in shadow contour on the ground, a virtual sensor named Shadow Projection Tunnel is designed. Then, multiple Shadow Projection Tunnels are generated according to the extracted silhouette information and corresponding light source positions. Finally, three-dimensional quadcopter positions and flight regimes are extracted based on the aggregation between multiple Shadow Projection Tunnels. The proposed method is validated to be accurate and efficient in monitoring quadcopter position and flight regimes based on the comparative analyses. In comparison with traditional quadcopter health monitoring methods, the proposed method has advantages on deployment convenience, system robustness, precision expandability, and scenario adaptability, making it an ideal solution for quadcopter monitoring in outdoor scenarios.

Passive lighting responsive three-dimensional integral imaging

A three dimensional (3D) integral imaging (II) technique with a real-time passive lighting responsive ability and vivid 3D performance has been proposed and demonstrated. Some novel lighting responsive phenomena, including light-activated 3D imaging, and light-controlled 3D image scaling and translation, have been realized optically without updating images. By switching the on/off state of a point light source illuminated on the proposed II system, the 3D images can show/hide independent of the diffused illumination background. By changing the position or illumination direction of the point light source, the position and magnification of the 3D image can be modulated in real time. The lighting responsive mechanism of the 3D II system is deduced analytically and verified experimentally. A flexible thin film lighting responsive II system with a 0.4 mm thickness was fabricated. This technique gives some additional degrees of freedom in order to design the II system and enable the virtual 3D image to interact with the real illumination environment in real time.

Stacking illumination of a confocal reflector light emitting diode automobile headlamp with an asymmetric triangular prism.

A confocal reflector lamp with an asymmetric triangular prism was designed for a stacking illumination of a light emitting diode (LED) automobile headlamp fitting ECE R112 asymmetrical regulation. The optical system includes three 1st elliptic reflectors, three 2nd parabolic reflectors, and one asymmetric triangular prism. Three elliptic and parabolic reflectors were assembled with three confocal reflector modules; two modules projected the cut-off line of a 0° angle, and the other module projected the cut-off line of a 15° angle using of an asymmetric triangular prism. The ray tracing, optical simulation, and mockup experiment results exhibited that the illumination distribution met the regulation of ECE R112 class B, and the ideal efficiency could reach 96.8% in theory. The tolerance analysis showed the efficiency remained above 98% under the error values of ±0.2 mm of the position of the LED light source, and the y direction of the up-down movement was more sensitive than the x and z directions. The measurement results of the mockup sample safety factor were all larger than 1.15 and supported the regulation of the ECE R112 Class B.

Editorial Issue 28.1

This issue contains five papers. In the first paper, Angel Zaldivar Pino, Manuel Gonzalez Bedia, and Francisco J. Seron, from Universidad Zaragoza, Spain, present a simulation framework in which the agents are endowed with a sensing device, an oscillator network as controller, and actuators to interact with the environment. The perception device is designed as an optic array emulating the principles of the animal retina, which assimilates stimuli resembling optic flow to be captured from the environment. The controller modulates informational variables to action variables in a sensory motor flow. Their approach is based on the Kuramoto model that describes mathematically a network of coupled phase oscillators and the use of evolutionary algorithms, which is proved to be capable of synthesizing minimal synchronization strategies based on the dynamical coupling between agents and environment. In the second paper, Congkun Chen, Yun Sheng, Fang Li, Guixu Zhang, from East China Normal University, Shanghai, China, and Hassan Ugail, from University of Bradford, UK, propose an extension of the use of the partial differential equation (PDE) method to head visualization with CT data and show how the two primary medical visualization means, surface reconstruction, and volume rendering can be integrated into one single framework through PDEs. Their scheme first performs head segmentation from CT slices using a variational approach; with the extracted boundary conditions, head surface reconstruction is then executed. Since only a few slices are used, their method can perform head surface reconstruction more efficiently in both computational time and storage cost than the widely used marching cubes algorithm. By elaborately introducing a third parameter ω to the PDE method, a solid head can be created, based on which the head volume is subsequently rendered with 3-D texture mapping. In the third paper, Francis Laclé, Utrecht University, the Netherlands, and Nicolas Pronost, Université Claude Bernard, Lyon, France, focus on combining, by a controllable enhancement process, a functional and biomechanical model of musculotendon units with its high-resolution geometrical counterpart. The method was developed in order to be invariant to spatial and polygonal configurations and to be scalable in both longitudinal and latitudinal directions. Results with 48 musculotendon units for the lower body show a drop of 84% with respect to the number of vertices when compared to the high-resolution model, while maintaining the functional information. A real-time simulation experiment resulted in a runtime of 135 Hz. Sergio Orts-Escolano, from University of Alicante, Spain, Johannes Bastiaan Boom, Xin Xin Ning, Steven McDonagh, Peter Sandilands, and Robert B. Fisher, from University of Edinburgh, UK, propose in the fourth paper, the first hybrid CPU-GPU based method for estimating a point light source position in a scene recorded by an RGB-D camera. The image and depth information from the Kinect is enough to estimate a light position in a scene, which allows for the rendering of synthetic objects into a scene that appear realistic enough for augmented reality purposes. This method does not require a light probe or other physical device. To make this method suitable for augmented reality, the authors developed a hybrid implementation that performs light estimation in less than 1 s. By rendering synthetic objects into the recorded scene, they illustrate that this accuracy is good enough for the rendered objects to look realistic. Finally, Jorge Eduardo Ramirez Flores and Antonio Susin Sanchez, from Universitat Politecnica de Catalunya, Barcelona, Spain, present an approach based on mesh segmentation for skinning and skeleton-driven computer animation. They propose a novel and fast method, based in watershed segmentation to deal with characters in T-Pose and arbitrary poses; they also introduce a simple weight assign algorithm based in the rigid skinning obtained with the segmentation algorithm for the linear blend skinning (LBS) deformation method. They ultimately propose a modified version of the LBS that avoids the loss of volume in twist rotations using the segmentation stage output values.

Light source optimization for automatic visual inspection of piston surface defects

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.

Optical signal processing for indoor positioning using a-SiCH technology

We use the nonlinear property of silicon carbon (SiC) multilayer devices under UV irradiation to design an optical processor for indoor positioning. The transducer combines the simultaneous demultiplexing operation with photodetection and self-amplification. The proposed coding is based on SiC technology. Based on that, we present a way to achieve indoor localization using the parity bits and a navigation syndrome. A representation with a 4-bit original string color message and the transmitted 7-bit string, the encoding and decoding of accurate positional information processes, and the design of SiC navigation syndrome generators are discussed and tested. A visible multilateration method estimates the position of the device using the decoded information received from several noncollinear transmitters. The location and motion information is found by mapping position and estimates the location areas. Since the indoor position of the light-emitting diode light source is known from building floor plans and lighting plans, the corresponding indoor position and travel direction of a mobile device can be determined.

Colour Helmholtz Stereopsis for Reconstruction of Dynamic Scenes with Arbitrary Unknown Reflectance

Helmholtz Stereopsis is a powerful technique for reconstruction of scenes with arbitrary reflectance properties. However, previous formulations have been limited to static objects due to the requirement to sequentially capture reciprocal image pairs (i.e. two images with the camera and light source positions mutually interchanged). In this paper, we propose colour Helmholtz Stereopsis—a novel framework for Helmholtz Stereopsis based on wavelength multiplexing. To address the new set of challenges introduced by multispectral data acquisition, the proposed Colour Helmholtz Stereopsis pipeline uniquely combines a tailored photometric calibration for multiple camera/light source pairs, a novel procedure for spatio-temporal surface chromaticity calibration and a state-of-the-art Bayesian formulation necessary for accurate reconstruction from a minimal number of reciprocal pairs. In this framework, reflectance is spatially unconstrained both in terms of its chromaticity and the directional component dependent on the illumination incidence and viewing angles. The proposed approach for the first time enables modelling of dynamic scenes with arbitrary unknown and spatially varying reflectance using a practical acquisition set-up consisting of a small number of cameras and light sources. Experimental results demonstrate the accuracy and flexibility of the technique on a variety of static and dynamic scenes with arbitrary unknown BRDF and chromaticity ranging from uniform to arbitrary and spatially varying.

English

A method for light sources estimation is proposed in this paper. The method utilizes feature points in cast shadows to estimate near light source positions from estimated source directions using specular highlights. There are several methods that can be used to estimate light sources from scene images, using either cast shadows or specular highlights. However, most of them are limited to directional light sources. The proposed method can estimate the positions and intensities of multiple near point light sources. Specular highlights on an object of known geometry are first used for light source direction estimation. Then, a discontinuity point in the object shape and the corresponding cast shadow on a ground plane are used for light source position estimation. Feature points obtained from an image of the cast shadow, however, can be inaccurate due to various factors. Information on diffused light reflected from Lambertian ground-plane surface is subsequently used to improve estimation accuracy. Experimental results were used to evaluate the performance of the proposed method.   Key words: Light source estimation, light source recovery, augmented reality.

Seeing "the Dress" in the Right Light: Perceived Colors and Inferred Light Sources.

In the well-known "dress" photograph, people either see the dress as blue with black stripes or as white with golden stripes. We suggest that the perception of colors is guided by the scene interpretation and the inferred positions of light sources. We tested this hypothesis in two online studies using color matching to estimate the colors observers see, while controlling for individual differences in gray point bias and color discrimination. Study 1 demonstrates that the interpretation of the dress corresponds to differences in perceived colors. Moreover, people who perceive the dress as blue-and-black are two times more likely to consider the light source as frontal, than those who see the white-and-gold dress. The inferred light sources, in turn, depend on the circadian changes in ambient light. The interpretation of the scene background as a wall or a mirror is consistent with the perceived colors as well. Study 2 shows that matching provides reliable results on differing devices and replicates the findings on scene interpretation and light sources. Additionally, we show that participants' environmental lighting conditions are an important cue for perceiving the dress colors. The exact mechanisms of how environmental lighting and circadian changes influence the perceived colors of the dress deserve further investigation.

Interaction with gravitropism, reversibility and lateral movements of phototropically stimulated potato shoots.

Phototropic (PT) and gravitropic (GT) bending are the two major tropic movements that determine the spatial position of potato shoots. We studied PT bending of potato plantlets grown under long-day photoperiods in several prearranged position setups providing different interactions with the GT response. Starting with the standard PT stimulation setup composed of unilateral irradiation of vertically positioned shoots, experiments were also done in antagonistic and synergistic setups and in treatments with horizontal displacement of the light source. In the standard setup, PT bending suppressed the GT bending, which could occur only if the PT stimulation was cancelled. The antagonistic position, with phototropism and gravitropism attempting to bend shoots in opposite directions, showed phototropism and gravitropism as independent bending events with the outcome varying throughout the day reflecting diurnal changes in the competence of individual tropic components. Whilst gravitropism was constant, phototropism had a marked daily fluctuation of its magnitude with a prominent morning maximum starting an hour after the dawn in the growth room and lasting for the next 6 h. When phototropism and gravitropism were aligned in a synergistic position, stimulating shoot bending in the same direction, there was little quantitative addition of their individual effects. The long period of morning PT bending maximum enabled multiple PT bending events to be conducted in succession, each one preceded by a separate lag phase. Studies of secondary PT events showed that potato plantlets can follow and adjust their shoot position in response to both vertical and horizontal movements of a light source. PT bending was reversible, since the 180° horizontal change of a blue light (BL) source position resulted in reversal of bending direction after a 20-min-long lag phase.Electronic supplementary materialThe online version of this article (doi:10.1007/s10265-016-0821-4) contains supplementary material, which is available to authorized users.

Online dosimetry for temoporfin-mediated interstitial photodynamic therapy using the canine prostate as model.

Online light dosimetry with real-time feedback was applied for temoporfin-mediated interstitial photodynamic therapy (PDT) of dog prostate. The aim was to investigate the performance of online dosimetry by studying the correlation between light dose plans and the tissue response, i.e., extent of induced tissue necrosis and damage to surrounding organs at risk. Light-dose planning software provided dose plans, including light source positions and light doses, based on ultrasound images. A laser instrument provided therapeutic light and dosimetric measurements. The procedure was designed to closely emulate the procedure for whole-prostate PDT in humans with prostate cancer. Nine healthy dogs were subjected to the procedure according to a light-dose escalation plan. About 0.15 mg/kg temoporfin was administered 72 h before the procedure. The results of the procedure were assessed by magnetic resonance imaging, and gross pathology and histopathology of excised tissue. Light dose planning and online dosimetry clearly resulted in more focused effect and less damage to surrounding tissue than interstitial PDT without dosimetry. A light energy dose-response relationship was established where the threshold dose to induce prostate gland necrosis was estimated from 20 to 30 J/cm2.

Anisotropic Ambient Volume Shading.

We present a novel method to compute anisotropic shading for direct volume rendering to improve the perception of the orientation and shape of surface-like structures. We determine the scale-aware anisotropy of a shading point by analyzing its ambient region. We sample adjacent points with similar scalar values to perform a principal component analysis by computing the eigenvectors and eigenvalues of the covariance matrix. In particular, we estimate the tangent directions, which serve as the tangent frame for anisotropic bidirectional reflectance distribution functions. Moreover, we exploit the ratio of the eigenvalues to measure the magnitude of the anisotropy at each shading point. Altogether, this allows us to model a data-driven, smooth transition from isotropic to strongly anisotropic volume shading. In this way, the shape of volumetric features can be enhanced significantly by aligning specular highlights along the principal direction of anisotropy. Our algorithm is independent of the transfer function, which allows us to compute all shading parameters once and store them with the data set. We integrated our method in a GPU-based volume renderer, which offers interactive control of the transfer function, light source positions, and viewpoint. Our results demonstrate the benefit of anisotropic shading for visualization to achieve data-driven local illumination for improved perception compared to isotropic shading.

A new method and device of aligning patient setup lasers in radiation therapy.

The aim of this study is to develop a new method to align the patient setup lasers in a radiation therapy treatment room and examine its validity and efficiency. The new laser alignment method is realized by a device composed of both a metallic base plate and a few acrylic transparent plates. Except one, every plate has either a crosshair line (CHL) or a single vertical line that is used for alignment. Two holders for radiochromic film insertion are prepared in the device to find a radiation isocenter. The right laser positions can be found optically by matching the shadows of all the CHLs in the gantry head and the device. The reproducibility, accuracy, and efficiency of laser alignment and the dependency on the position error of the light source were evaluated by comparing the means and the standard deviations of the measured laser positions. After the optical alignment of the lasers, the radiation isocenter was found by the gantry and collimator star shots, and then the lasers were translated parallel to the isocenter. In the laser position reproducibility test, the mean and standard deviation on the wall of treatment room were 32.3±0.93 mm for the new method whereas they were 33.4±1.49 mm for the conventional method. The mean alignment accuracy was 1.4 mm for the new method, and 2.1 mm for the conventional method on the walls. In the test of the dependency on the light source position error, the mean laser position was shifted just by a similar amount of the shift of the light source in the new method, but it was greatly magnified in the conventional method. In this study, a new laser alignment method was devised and evaluated successfully. The new method provided more accurate, more reproducible, and faster alignment of the lasers than the conventional method.PACS numbers: 87.56.Fc, 87.53.Bn, 87.53.Kn, 87.53.Ly, 87.55.Gh

Interactive light source position estimation for augmented reality with an RGB‐D camera

AbstractThe first hybrid CPU‐GPU based method for estimating a point light source position in a scene recorded by an RGB‐D camera is presented. The image and depth information from the Kinect is enough to estimate a light position in a scene, which allows for the rendering of synthetic objects into a scene that appears realistic enough for augmented reality purposes. This method does not require a light probe or other physical device. To make this method suitable for augmented reality, we developed a hybrid implementation that performs light estimation in under 1second. This is sufficient for most augmented reality scenarios because both the position of the light source and the position of the Kinect are typically fixed. The method is able to estimate the angle of the light source with an average error of 20°. By rendering synthetic objects into the recorded scene, we illustrate that this accuracy is good enough for the rendered objects to look realistic. Copyright © 2015 John Wiley & Sons, Ltd.