Improved Computation of Attenuated Light with Application in Scenes with Many Light Sources

The grand challenge for the global illumination community is the successful rendering of complex scenes containing arbitrary reflectance properties and numerous light sources. Even for completely diffuse scenes, high geometric complexity and large numbers of light sources present a problem which current algorithms cannot solve in a practical amount of time. However, recent research by Rushmeier et. al. [7] utilizes geometric simplification to offer a promising solution to the problem of high geometric complexity and work by Shirley et. al. [9, 10] presents shadow ray optimization techniques for efficient handling of large numbers of luminaires. We present an approach which combines and improves upon ideas from these works. Our work adds to the growing toolbox of importance sampling techniques used in realistic image synthesis (e.g. [4, 14]).

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.

For a long time shape from shading had problems to work on real scenes. It was formulated with too simplified physical models which made its application to real scenes difficult and the integration with other modules inconsistent because the physical models of the other modules were more complex and different. These limiting physical models have been: the orthogonal projection, the restriction to a light source at infinity and the lambertian diffusion mode. It also could only calculate either depth or photometric characteristics. One of them had to be known, which is a priori difficult for real scenes. This work present shape from shading in a general formulation using more complex physical models which can cope with the complexity of real scenes and which are consistent with other modules. The physical models are: the perspective projection, point light sources and ambient light as well as the Phong's reflection model dealing with diffuse and specular reflection. In order to overcome the problem of the shape from shading module to be ill-posed and to calculate consistently both depth and photometric characteristics at the same time we use stereo photometry and the cooperation with stereo vision.

The number of luminaires in an office in the field of lighting design is usually determined with the lumen method, which uses utilization factors. These factors are calculated by luminous flux incident on the working plane to that irradiated from the light source, assuming a non-obstructed room. Lighting design techniques with the lumen method are very useful if they are applied to an office with fixtures and task ambient lighting, which is a combination of local-lighting and general-lighting systems. We applied lighting design to a working plane within shadow under task ambient lighting, and paid attention to utilization factors with the lumen method. That is, we evaluated the correction coefficients where the utilization factors in setting up fixtures and a shadow caster (i.e., a globe the size of a human head) could easily be predicted by multiplying the utilization factors for a non-obstructed office and the correction coefficients. The utilization factors using the lumen method on the working plane within shadow for ambient light sources and a task light source were first examined based on results derived from illuminance calculations using the Monte Carlo method that treats notion of the luminous flux as a set of numerous particles. The validity of correction coefficients used to calculate utilization factors within shadow under task ambient lighting was then evaluated. As a result, utilization factors within shadow can be predicted by simply multiplying them by the correction coefficients in non-obstructed rooms with ambient light sources or from direct components without a shadow caster for a task light source.

22 - LEDs for projectors

Light-Source Modeling Using Pyramidal Light Maps

Transmitting information with visible light requires controlling the intensity of the light source. Many light sources in our environments, however, cannot be controlled (not only the sun but also plenty of light bulbs). These uncontrollable light sources provide an immense amount of ambient light that could be used for wireless communication, yet few studies are exploiting this opportunity. We provide a detailed analysis of a Hardware- and Physical-Layer to create safe and reliable wireless links relying solely on ambient light and simple photosensors. Motivated by recent studies, our platform builds upon liquid crystal displays (LCDs) to backscatter ambient light, but it provides a unique and novel feature: our platform utilizes frequency signals to modulate ambient light. Compared to the state-of-the-art, which rely on either pulse- or color-based modulation, our approach allows us to provide simultaneously: a simple and energy-efficient platform (no cameras), flicker-free communication (safe), and the ability to work reliably in spite of the interference and light fluctuations caused by uncontrollable light sources (reliable). We test our platform in indoor and outdoor environments, and show that an LCD surface of 6×8 cm can transmit 80 bps at ranges between 4 meters (indoors) and 60 meters (outdoors), consuming a fraction of the energy required by comparable systems using cameras.

Graphs play an increasingly important role in various big data applications. However, existing graph data structures cannot simultaneously address the performance bottlenecks caused by the dynamic updates, large scale, and high query complexity of current graphs. This paper proposes a novel data structure for large-scale dynamic graphs called CuckooGraph. It does not require any prior knowledge of the upcoming graphs, and can adaptively resize to the most memory-efficient form while requiring few memory accesses for very fast graph data processing. The key techniques of CuckooGraph include TRANSFORMATION and DENYLIST. TRANSFORMATION fully utilizes the limited memory by designing related data structures that allow flexible space transformations to smoothly expand/tighten the required space depending on the number of incoming items. DENYLIST efficiently handles item insertion failures and further improves processing speed. Our experimental results show that compared with the most competitive solution Spruce, Cuckoo-Graph achieves about 33× higher insertion throughput while requiring only about 68% of the memory space.

Inverse rendering, a technique for reconstructingthree-dimensional (3D) geometric structures and surface materials from two-dimensional (2D) images, is of great significance in fields such as robotic manipulation, virtual reality, and augmented reality. However, existing inverse rendering methods based on neural implicit representations are primarily suitable for scenarios with fixed light sources and struggle with dynamic point lighting. This paper introduces a novel 3D inverse rendering method that estimates the positions of point light sources, facilitating the 3D reconstruction of geometrical structures and the determination of light source locations from a collection of images captured from various perspectives, even under dynamic illumination conditions from an unknown point light source.

Surface exploration by the distributed robots is a countermeasure way to the solo exploration by using a large and expensive rover. The distributed rover can explore a large area at the same time, and it is expected to improve the exploration speed. However, the mass resource of the distributed small rover is limited. A small and lightweight position and attitude estimation system is also required for rover guidance and control. In this paper, we propose a compact, lightweight attitude and position estimation system for distributed rover using light from the leader agent. A small photodiodes are used as a sensor of a position estimation system using light for the small exploration rover. Photodiodes mounted on the follower rover in different directions detect the light from the leader to estimate the vector in the light source direction with respect to the rover body coordinate system. The attitude is decided by using the estimated light source direction vector and the gravitational vector by the acceleration sensor in the rover. After determining the attitude, the distance between the leader rover and the follower rover is estimated using the elevation angle of the light source and the light source height information. If there is communication between the leader and followers, more complicated mutual position recognition is possible, but here we discuss the limits that can be achieved with minimum hardware. We also describe the light source recognition from the leader rover under ambient light, and also discuss the overall scheme of the exploration system.

Tracheal intubation is older than the recognized his-tory of general anesthesia itself. In the late 18th cen-tury, The Royal Humane Society of London used tra-cheal intubation for resuscitating the near-drowned.Approximately 100 years later, MacEwan (1) per-formed a digital tracheal intubation in an awake pa-tient before a chloroform and air general endotrachealanesthetic for the resection of a tongue tumor, and in1928, Magill (2) incorporated blind nasal tracheal in-tubation as a part of a general anesthetic. Althoughlaryngoscopes were invented in the 19th century, tra-cheal intubation under direct visualization was greatlyenhanced by the development of a special laryngo-scope blade by Macintosh (3) in 1943.The first reported use of a lighted stylet used tofacilitate intubation came in 1957 when (by now SirRobert) Macintosh (4) described an 18-inch illumi-nated tracheal tube introducer, which was designed tostiffen the tube and better illuminate the cords bysupplementing the light of the laryngoscope. Berman(5) described a similar device in 1959 and said it wasuseful “when the fickle light of the laryngoscope hasgone out at the most inopportune time.” In the sameyear, Yamamura et al. (6) described a light bulb-tippedwire that was inserted into the tracheal tube beforeblind nasal intubation in awake patients. The tubeposition was then determined by the medial transillu-mination of the external throat and neck.In 1977, Foster (7) used a transilluminating fiberop-tic bundle to facilitate tracheal intubation in a youngchild with trismus, and Ducrow (8), in the followingyear, used a flexible surgical light (Flexi-lum™, Con-cept Corporation, Clearwater, FL) to achieve the sameend by first passing a guide (two plastic suction cath-eters connected end-to-end) into the trachea followedby passage of the tracheal tube over the guide. In acorrespondence to the latter article, Rayburn (9) com-mented that the Flexi-lum™ could be positioned in-side the tracheal tube, thereby shortening the intuba-tion sequence and claimed that the technique,nicknamed “lightwand intubation,” had been used forsome years at the Brooke Army Medical Center.

We present a light position calibration technique based on a general arrangement of at least two reflective spheres in a single image. Contrary to other techniques we do not directly intersect rays for triangulation but instead solve for the optimal light position by evaluating the image-space error of the light highlights reflected from the spheres. This approach has been very successful in the field of Structure-from-Motion estimation. It has not been applied to light source calibration because determining the reflection point on the sphere to project the highlight back in the image is a challenging problem. We show a solution and define a novel, non-linear error function to recover the position of a point light source. We also introduce a light position estimation that is based on observing the light source directly in multiple images which does not use any reflections. Finally, we evaluate both proposed techniques and the classical ray intersection method in several scenarios with real data.

In a scene observed from a fixed viewpoint, the set of shadow curves in an image changes as a point light source (nearby or at infinity) assumes different locations. We show that for any finite set of point light sources illuminating an object viewed under either orthographic or per- spective projection, there is an equivalence class of object shapes having the same set of shadows. Members of this equivalence class differ by a four parameter family of projective transformations, and the shadows of a transformed object are identical when the same transformation is applied to the light source locations. Under orthographic projection, this family is the generalized bas-relief (GBR) transformation, and we show that the GBR transformation is the only family of transformations of an object’s shape for which the complete set of imaged shadows is identical. Furthermore, for objects with Lambertian surfaces illuminated by dis- tant light sources, the equivalence class of object shapes which preserves shadows also preserves surface shading. Finally, we show that given mul- tiple images under differing and unknown light source directions, it is possible to reconstruct an object’s shape up to these transformations from the shadows alone.KeywordsLight SourceProjective TransformationCast ShadowPoint Light SourceCamera CenterThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

The graph model enables a broad range of analysis, thus graph processing is an invaluable tool in data analytics. At the heart of every graph-processing system lies a concurrent graph data structure storing the graph. Such a data structure needs to be highly efficient for both graph algorithms and queries. Due to the continuous evolution, the sparsity, and the scale-free nature of real-world graphs, graph-processing systems face the challenge of providing an appropriate graph data structure that enables both fast analytical workloads and low-memory graph mutations. Existing graph structures offer a hard trade-off between read-only performance, update friendliness, and memory consumption upon updates. In this paper, we introduce CSR++, a new graph data structure that removes these trade-offs and enables both fast read-only analytics and quick and memory-friendly mutations. CSR++ combines ideas from CSR, the fastest read-only data structure, and adjacency lists to achieve the best of both worlds. We compare CSR++ to CSR, adjacency lists from the Boost Graph Library, and LLAMA, a state-of-the-art update-friendly graph structure. In our evaluation, which is based on popular graph-processing algorithms executed over real-world graphs, we show that CSR++ remains close to CSR in read-only concurrent performance (within 10% on average), while significantly outperforming CSR (by an order of magnitude) and LLAMA (by almost 2×) with frequent updates.

We discuss the sources and levels of background light that should be expected on space based laser communication (lasercom) crosslinks and uplinks, as well as on downlinks to ground stations. The analyses are valid for both Earth orbiting satellites and inter-planetary links. Fundamental equations are derived suitable for first order system engineering analyses of potential lasercom systems. These divide sources of background light into two general categories: extended sources which fill the field of view of a receiver’s optics, and point sources which cannot be resolved by the optics. Specific sources of background light are discussed, and expected power levels are estimated. For uplinks, reflected sunlight and blackbody radiation from the Earth dominates. For crosslinks, depending on specific link geometry, sources of background light may include the Sun in the field of view (FOV), reflected sunlight and blackbody radiation from planets and other bodies in the solar system, individual bright stars in the FOV, the amalgam of dim stars in the FOV, zodiacal light, and reflected sunlight off of the transmitting spacecraft. For downlinks, all of these potentially come into play, and the effects of the atmosphere, including turbulence, scattering, and absorption contribute as well. Methods for accounting for each of these are presented. Specific examples are presented to illustrate the relative contributions of each source for various link geometries.