Virtual Light Source Research Articles

A virtual reality design for learning the basic concepts of synchrotron light source

This study investigated the virtual reality technology to develop a virtual synchrotron light source model and its learning contents for applications in the curriculum of science and life technology in elementary and junior high schools. The objective is to increase the interest and effectiveness of young students in learning this advanced technology and its applications. The factors of student age, gender and correlation with the performance in previous science courses were also investigated to see if they would affect the learning effectiveness. A teaching experiment was conducted and the results showed that the model was effective in helping students understand the basic concepts of synchrotron light source and its applications. Student age and gender had no obvious influence on the learning achievement, but a significant positive correlation was found between students' performance in their previous science courses and the learning achievement. Also, the questionnaire results revealed that most students were very interested in using the virtual light source model and its learning contents.

Photon streaming for interactive global illumination in dynamic scenes

While many methods exist for simulating diffuse light inter-reflections, relatively few of them are adapted to dynamic scenes. Despite approximations made on the formal rendering equation, managing dynamic environments at interactive or real-time frame rates still remains one of the most challenging problems. This paper presents a lighting simulation system based on photon streaming, performed continuously on the central processor unit. The power corresponding to each photon impact is accumulated onto predefined points, called virtual light accumulators (or VLA). VLA are used during the rendering phase as virtual light sources. We also introduce a priority management system that automatically adapts to brutal changes during lighting simulation (for instance due to visibility changes or fast object motion). Our system naturally benefits from multi-core architecture. The rendering process is performed in real time using a graphics processor unit, independently from the lighting simulation process. As shown in the results, our method provides high framerates for dynamic scenes, with moving viewpoint, objects and light sources.

Pencil Sketch Painting with Virtual Point Light Source on Image Plane

Pencil Sketch is a common artistic form which expresses the objects in the world by single color lines.The emphases in pencil sketch paintings are the high light and shadow regions which can be used to express the scene levels.The artists often exaggerate these light and shadow regions by artistic styles,to express the subject of their paintings better.This paper introduces a method to estimate the position of a virtual point light on 2D image plane,it computes the location of the virtual point light by distance field as well as luminance field to minimize the influence of luminance gradient field of source image.This paper also introduces a shadow enhanced method based on 2D virtual point light,by enhancing the contrast of light and shadow in real image,to illustrate the shading effect in pencil sketch paintings.With this method,the generated sketch paintings may achieve more contrast on the objects' edges,thus the final rendering images may obtain more characteristics of pencil sketch paintings.

Mapping local optical densities of states in silicon photonic structures with nanoscale electron spectroscopy

Relativistic electrons in a structured medium generate radiative losses such as Cherenkov and transition radiation that act as a virtual light source, coupling to the photonic densities of states. The effect is most pronounced when the imaginary part of the dielectric function is zero, a regime where in a nonretarded treatment no loss or coupling can occur. Maps of the resultant energy losses as a sub-5 nm electron probe scans across finite waveguide structures reveal spatial distributions of optical modes in a spectral domain ranging from near infrared to far ultraviolet.

Optical simulation study on the effect of reflecting properties of reflection films on the performances of collimating films for the LCD backlight applications

The dependence of optical performances of collimating films such as prism films and pyramid films on the reflecting properties of reflection films were investigated by using a ray tracing technique. The angular distribution of the luminance and the on‐axis luminance gain were obtained by using a simple backlight model composed of a reflection film, a virtual flat light source, and a collimating film. Three kinds of reflecting properties were used, which were a perfect Lambertian reflector, a perfect mirror reflector, and a reflector having both diffuse and specular properties. It was found that the on‐axis luminance gain was the highest in the simulation where a mirror reflector was used, while the viewing angle was the widest where the Lambertian reflector was used. This result indicates that it is necessary to optimize the simulation condition such as the reflecting properties in order to predict the optical performances of collimating films accurately. Quantitative correlation between the optical characteristics of collimating films and the reflecting properties of reflection films can be used to improve simulation technique for the development and the optimization of collimating films for LCD backlight applications.

Effect of smoking on the gingival capillary density: assessment of gingival capillary density with orthogonal polarization spectral imaging

Microvascular changes because of smoking are frequently presumed in models because of the negative effect of smoking portrayed on the microcirculation. We hypothesized that cigarette smoke might lead to a decrease in gingival capillary density. Capillary density was assessed with orthogonal polarization spectral (OPS) imaging, a technique using special optics by which a virtual light source is created at a depth of 1 mm within the mucosa. The light is absorbed by haemoglobin, resulting in an image of the capillaries in negative contrast. The gingival capillary density was measured in 20 healthy male dental students with a mean age of 25. Ten of the students were smokers and 10 were non-smokers. In each subject six images of the right maxillary pre-molar region were obtained, and the mean gingival capillary density was determined through the use of K&K software technology. The mean capillary density in smokers was 69.3 +/- 8.9 capillaries per visual field compared with a mean capillary density in non-smokers of 60.6 +/- 5.4 (p=0.33). No significant differences were found between the gingival capillary density of smokers and non-smokers.

Multibeam long-path differential optical absorption spectroscopy instrument: a device for simultaneous measurements along multiple light paths

A novel long-path differential optical absorption spectroscopy (DOAS) apparatus for measuring tropospheric trace gases and the first results from its use are presented: We call it the multibeam instrument. It is the first active DOAS device that emits several light beams simultaneously through only one telescope and with only one lamp as a light source, allowing simultaneous measurement along multiple light paths. In contrast to conventional DOAS instruments, several small mirrors are positioned near the lamp, creating multiple virtual light sources that emit one light beam each in one specific direction. The possibility of error due to scattering between the light beams is negligible. The trace-gas detection limits of NO2, SO2, O3, and H2CO are similar to those of the traditional long-path DOAS instrument.

Real‐time Light Animation

Abstract Light source animation is a particularly hard field of real‐time global illumination algorithms since moving light sources result in drastic illumination changes and make coherence techniques less effective. However, the animation of small (point‐like) light sources represents a special but practically very important case, for which the reuse of the results of other frames is possible. This paper presents a fast light source animation algorithm based on the virtual light sources illumination method. The speed up is close to the length of the animation, and is due to reusing paths in all frames and not only in the frame where they were obtained. The possible applications of this algorithm are the lighting design and systems to convey shape and features with relighting.

Spectral characteristics of light sources for S-cone stimulation.

Electrophysiological investigations of the short-wavelength sensitive pathway of the human eye require the use of a suitable light source as a S-cone stimulator. Different light sources with their spectral distribution properties were investigated and compared with the ideal S-cone stimulator. First, the theoretical background of the calculation of relative cone energy absorption from the spectral distribution function of the light source is summarized. From the results of the calculation, the photometric properties of the ideal S-cone stimulator will be derived. The calculation procedure was applied to virtual light sources (computer generated spectral distribution functions with different medium wavelengths and spectrum widths) and to real light sources (blue and green light emitting diodes, blue phosphor of CRT-monitor, multimedia projector, LCD monitor and notebook display). The calculated relative cone absorbencies are compared to the conditions of an ideal S-cone stimulator. Monochromatic light sources with wavelengths of less than 456 nm are close to the conditions of an ideal S-cone stimulator. Spectrum widths up to 21 nm do not affect the S-cone activation significantly (S-cone activation change < 0.2%). Blue light emitting diodes with peak wavelength at 448 nm and spectrum bandwidth of 25 nm are very useful for S-cone stimulation (S-cone activation approximately 95%). A suitable display for S-cone stimulation is the Trinitron computer monitor (S-cone activation approximately 87%). The multimedia projector has a S-cone activation up to 91%, but their spectral distribution properties depends on the selected intensity. LCD monitor and notebook displays have a lower S-cone activation (< or = 74%). Carefully selecting the blue light source for S-cone stimulation can reduce the unwanted L-and M-cone activation down to 4% for M-cones and 1.5% for L-cones.

Flexible Image-Based Photometric Reconstruction using Virtual Light Sources

Photometric reconstruction is the process of estimating the illumination and surface reflectance properties of an environment, given a geometric model of the scene and a set of photographs of its surfaces. For mixed-reality applications, such data is required if synthetic objects are to be correctly illuminated or if synthetic light sources are to be used to re-light the scene. Current methods of estimating such data are limited in the practical situations in which they can be applied, due to the fact that the geometric and radiometric models of the scene which are provided by the user must be complete, and that the position (and in some cases, intensity) of the light sources must also be specified a-priori. In this paper, a novel algorithm is presented which overcomes these constraints, and allows photometric data to be reconstructed in less restricted situations. This is achieved through the use of virtual light sources which mimic the effect of direct illumination from unknown luminaires, and indirect illumination reflected off unknown geometry. The intensity of these virtual light sources and the surface material properties are estimated using an iterative algorithm which attempts to match calculated radiance values to those observed in photographs. Results are presented for both synthetic and real scenes that show the quality of the reconstructed data and its use in off-line mixed-reality applications.

Interactive virtual relighting of real scenes

Computer augmented reality (CAR) is a rapidly emerging field which enables users to mix real and virtual worlds. Our goal is to provide interactive tools to perform common illumination, i.e., light interactions between real and virtual objects, including shadows and relighting (real and virtual light source modification). In particular, we concentrate on virtually modifying real light source intensities and inserting virtual lights and objects into a real scene; such changes can be very useful for virtual lighting design and prototyping. To achieve this, we present a three-step method. We first reconstruct a simplified representation of real scene geometry using semiautomatic vision-based techniques. With the simplified geometry, and by adapting recent hierarchical radiosity algorithms, we construct an approximation of real scene light exchanges. We next perform a preprocessing step, based on the radiosity system, to create unoccluded illumination textures. These replace the original scene textures which contained real light effects such as shadows from real lights. This texture is then modulated by a ratio of the radiosity (which can be changed) over a display factor which corresponds to the radiosity for which occlusion has been ignored. Since our goal is to achieve a convincing relighting effect, rather than an accurate solution, we present a heuristic correction process which results in visually plausible renderings. Finally, we perform an interactive process to compute new illumination with modified real and virtual light intensities.

An automatic crowd generation system using image processing techniques

In advertisements, movies, and virtual environment modeling, synthetic crowd generation and processing techniques are needed. Currently, the most common crowd generation techniques are simply overlaying pre-captured crowd images onto the background image. In this paper we introduce an automatic method to generate realistic crowds. The system handles the data of a person's image and its attributes in a database to merge with background image. The method includes: (1) zooming an image in/out, depending on the distance from virtual viewport to the center of an image; (2) blurring an image boundary; (3) shadowing an image of person with a virtual light source; and (4) mirroring an image. We also propose various distribution functions to make a realistic crowd model and give implementation results. Improvements in the system for virtual reality applications on the WWW are being studied.

A Light Hierarchy for Fast Rendering of Scenes with Many Lights

We introduce a new data structure in the form of a light hierarchy for efficiently ray-tracing scenes with many light sources. An octree is constructed with the point light sources in a scene. Each node represents all the light sources it contains by means of a virtual light source. We determine bounds on the error committed with this approximation to shade a point, both for the cases of diffuse and specular reflections. These bounds are then used to guide a hierarchical shading algorithm. If the current level of the light hierarchy provides shading of sufficient quality, the approximation is used, thus avoiding the cost of shading for all the light sources contained below this level. Otherwise the descent into the light hierarchy continues. Our approach has been implemented for scenes without occlusion. The results show important acceleration compared to standard ray-tracing (up to 90 times faster) and an important improvement compared to Ward’s adaptive shadow testing.

ＶＲを支える映像情報メディア技術 光線記述に基づく仮想光源画像の合成

The ray-based approach is powerful and useful for the description of 3-D images because of its neutrality to all types of 3-D displaying technologies This approach has been developed in order to reproduce the whole visual data captured at the transmitter However, for the purpose of augmented reality, not only is the reproduction of real visual data essential, but also the synthesis of virtual visual data For example, you may want to change the lightening condition of a scene which has already been captured in some photographs The goal of this work is to synthesize a virtual scene, in which we can easily move light sources The key feature is that the virtual scene is synthesized only from the photographs. From this point of view, this paper extends the concept of the ray-based description of 3-D visual data in order to cope with virtual light sources Experimental results show the potential applicability of this method to the augmented spatial communication systems.

Compact high‐efficiency nonimaging back reflector design for filament light sources

When filament light sources are used in nonimaging luminaires that are intended to ensure prescribed angular control and high optical efficiency, a 3-D back reflector must often be incorporated, so as to redirect rays emitted by the filaments that would otherwise miss the luminaire entrance aperture. The glass envelope precludes the filaments from filling the luminaire entrance aperture. The introduction of a back reflector can serve to create a virtual light source, away from the actual grid of filaments, which mitigates the problem. The back reflector should be compact, with high radiative efficiency, namely, a small number of reflections while accommodating all rays. We develop a new nonimaging back reflector design comprised of multiple rotated elliptical arcs in a rotationally symmetric device that is a good compromise.

Applications of three-dimensional display techniques in medical imaging

This paper outlines some of the current uses of three-dimensional techniques in medical imaging applications and their potential for the future. As an example, three-dimensional imaging is described using a CT scanner, as it applies to a case involving craniofacial surgery. This includes defining the relationship between the requirements on the data acquisition system, as well as the specification of the hardware and software for the display. A currently used algorithm is described for the display of surfaces as a function of local position, orientation of the surface and the position of a virtual light source. This includes the use of transparency and cut plane greyscale techniques, in addition to the display of the surfaces. A speculation is made regarding the use of a three-dimensional display as the standard viewing mode in CT, with slice and multiplanar imaging as submodes.

Two-dimensional remote air-pollution monitoring via tomography

We propose to apply computerized tomography to measure a two-dimensional pollutant-concentration map over an area that may contain several potential sources of pollution. A tunable-laser source at the center of the area generates secondary or virtual light sources around the perimeter of the area that play the role of x rays in conventional computerized tomography of the human body.