Continuous collision detection (CCD) between deforming triangle mesh elements in 3D is a critical tool for many applications. The standard method involving a cubic polynomial solver is vulnerable to rounding error, requiring the use of ad hoc tolerances, and nevertheless is particularly fragile in (near-)planar cases. Even with per-simulation tuning, it may still cause problems by missing collisions or erroneously flagging non-collisions. We present a geometrically exact alternative guaranteed to produce the correct Boolean result (significant collision or not) as if calculated with exact arithmetic, even in degenerate scenarios. Our critical insight is that only the parity of the number of collisions is needed for robust simulation, and this parity can be calculated with simpler non-constructive predicates. In essence we analyze the roots of the nonlinear system of equations defining CCD through careful consideration of the boundary of the parameter domain. The use of new conservative culling and interval filters allows typical simulations to run as fast as with the non-robust version, but without need for tuning or worries about failure cases even in geometrically degenerate scenarios. We demonstrate the effectiveness of geometrically exact detection with a novel adaptive cloth simulation, the first to guarantee to remain intersection-free despite frequent curvature-driven remeshing.

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Efficient geometrically exact continuous collision detection

In computer graphics, ray tracing has become a powerful tool for generating realistically looking images. Even though ray tracing offers high flexibility, a logarithmic scalability in scene complexity, and is known to be efficiently parallelizable, its demand for compute power has in the past lead to its limitation to high-quality off-line rendering. This thesis focuses on the question of how realtime ray tracing can be realized on current processor architectures. To this end, it provides a detailed analysis of the weaknesses and strengths of current processor architectures, for the purpose of allowing for highly optimized implementation. The combination of processor-specific optimizations with algorithms that exploit the coherence of ray tracing, makes it possible to achieve realtime performance on a single CPU. Besides the optimization of the ray tracing algorithm itself, this thesis focuses on the efficient building of spatial index structures. By building these structures from scratch for every frame, interactive ray tracing of fully dynamic scenes becomes possible. Moreover, a parallelization framework for ray tracing is discussed that efficiently exploits the compute power of a cluster of commodity PCs. Finally, a global illumination algorithm is proposed that efficiently combines optimized ray tracing and the parallelization framework. The combination makes it possible to compute complete global illumination at interactive frame rates.

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Realtime ray tracing on current CPU architectures

Tone-mapping constitutes a key component within the field of high dynamic range HDR imaging. Its importance is manifested in the vast amount of tone-mapping methods that can be found in the literature, which are the result of an active development in the area for more than two decades. Although these can accommodate most requirements for display of HDR images, new challenges arose with the advent of HDR video, calling for additional considerations in the design of tone-mapping operators TMOs. Today, a range of TMOs exist that do support video material. We are now reaching a point where most camera captured HDR videos can be prepared in high quality without visible artifacts, for the constraints of a standard display device. In this report, we set out to summarize and categorize the research in tone-mapping as of today, distilling the most important trends and characteristics of the tone reproduction pipeline. While this gives a wide overview over the area, we then specifically focus on tone-mapping of HDR video and the problems this medium entails. First, we formulate the major challenges a video TMO needs to address. Then, we provide a description and categorization of each of the existing video TMOs. Finally, by constructing a set of quantitative measures, we evaluate the performance of a number of the operators, in order to give a hint on which can be expected to render the least amount of artifacts. This serves as a comprehensive reference, categorization and comparative assessment of the state-of-the-art in tone-mapping for HDR video.

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A comparative review of tone-mapping algorithms for high dynamic range video

Recent subjective studies showed that current tone mapping operators either produce disturbing temporal artifacts, or are limited in their local contrast reproduction capability. We address both of these issues and present an HDR video tone mapping operator that can greatly reduce the input dynamic range, while at the same time preserving scene details without causing significant visual artifacts. To achieve this, we revisit the commonly used spatial base-detail layer decomposition and extend it to the temporal domain. We achieve high quality spatiotemporal edge-aware filtering efficiently by using a mathematically justified iterative approach that approximates a global solution. Comparison with the state-of-the-art, both qualitatively, and quantitatively through a controlled subjective experiment, clearly shows our method's advantages over previous work. We present local tone mapping results on challenging high resolution scenes with complex motion and varying illumination. We also demonstrate our method's capability of preserving scene details at user adjustable scales, and its advantages for low light video sequences with significant camera noise.

Temporally coherent local tone mapping of HDR video

One of the main goals of digital imagery is to improve the capture and the reproduction of real or synthetic scenes on display devices with restricted capabilities. Standard imagery techniques are limited with respect to the dynamic range that they can capture and reproduce. High Dynamic Range (HDR) imagery aims at overcoming these limitations by capturing, representing and displaying the physical value of light measured in a scene. However, current commercial displays will not vanish instantly hence backward compatibility between HDR content and those displays is required. This compatibility is ensured through an operation called tone mapping that retargets the dynamic range of HDR content to the restricted dynamic range of a display device. Although many tone mapping operators exist, they focus mostly on still images. The challenges of tone mapping HDR videos are more complex than those of still images since the temporal dimensions is added. In this work, the focus was on the preservation of temporal coherency when performing video tone mapping. Two main research avenues are investigated: the subjective quality of tone mapped video content and their compression efficiency. Indeed, tone mapping independently each frame of a video sequence leads to temporal artifacts. Those artifacts impair the visual quality of the tone mapped video sequence and need to be reduced. Through experimentations with HDR videos and Tone Mapping Operators (TMOs), we categorized temporal artifacts into six categories. We tested video tone mapping operators (techniques that take into account more than a single frame) on the different types of temporal artifact and we observed that they could handle only three out of the six types. Consequently, we designed a post-processing technique that adapts to any tone mapping operator and reduces the three types of artifact not dealt with. A subjective evaluation reported that our technique always preserves or increases the subjective quality of tone mapped content for the sequences and TMOs tested. The second topic investigated was the compression of tone mapped video content. So far, work on tone mapping and video compression focused on optimizing a tone map curve to achieve high compression ratio. These techniques changed the rendering of the video to reduce its entropy hence removing any artistic intent or constraint on the final results. That is why, we proposed a technique that reduces the entropy of a tone mapped video without altering its rendering.

/pdf/temporal-coherency-for-video-tone-mapping-qyorjws5fd.pdf

Temporal coherency for video tone mapping

Ray tracing and other techniques employ algorithms which require the intersection between a three-dimensional parametric ray and an object to be computed. The object to intersect is typically a sphere, triangle, or polygon but many surface types are possible. In this work we consider intersections between rays and the simplest parametric surface, the bilinear patch. Unlike other surfaces, solving the ray-bilinear patch intersection with simple algebraic manipulations fails. We present a complete, efficient, robust, and graceful formulation to solve ray-bilinear patch intersections quickly. Source code is available online.

Ray Bilinear Patch Intersections

Monitor intensity ranges are much lower than the range of intensities in the real world or even in high quality renderings. Rendering in high dynamic range (HDR) is becoming more common in computer graphics. HDR video cameras are also available. The process of compressing a single frame of HDR data (real or synthetic) into a range displayable by monitors is called tone mapping. Videos (a real or synthetic sequence of images) require this technique as well. Tone mapping video introduces a temporal constraint to maintain consistent intensities between frames. We present a novel method, called adaptive temporal tone mapping, which provides smooth intensity transitions in tone mapped video, while allowing for discontinuous dynamic lighting changes (such as turning on a light or exiting a tunnel).

Adaptive temporal tone mapping

Surface models containing billions of polygons are becoming more frequent in computer graphics. Mesh simplification is necessary for displaying such surfaces at interactive rates. We describe a novel method for simplifying polyhedral meshes while producing multiple levels of detail for progressive transmission and interactive exploration. Unlike previous work on mesh simplification, our method is not restricted to triangle meshes. We propose a highly efficient edge-collapsing algorithm for meshes composed of non-planar multi-sided polygons based on a simple edge-selection strategy.

Simplification of Arbitrary Polyhedral Meshes

Abstract:In Phaedrus, Plato invokes a mythic exemplum concerning the Egyptian deity Thoth. Though often interpreted as an overt critique of writing, this argument posits Thoth is offered analogically to contrast Plato’s rhetorical epistemology with that of the ancient Egyptians. To do so, this argument addresses why a mythic Egyptian figure might be so significant to Plato in the 4th Century B.C. Greece, whose culture already had multiple gods and cultural heroes to whom the invention of writing is attributed, when the episode in Phaedrus is axiomatically described as a critique of writing. Because Plato may have had some degree of firsthand knowledge of Egyptian traditions it explores those traditions personified in the figure of Thoth, which should be examined as an analogical device advised by Egyptian rhetorical epistemology. A closer examination of the comparative rhetorical epistemological perspective not only illuminates Thoth’s appearance in Phaedrus but also the Egyptian rhetorical-epistemic tradition. Thoth’s role as epistemic mediator between humans and truth, in the broadest terms, was to act as psychopomp who moves both between humanity and the arrival at knowledge that prefigures rhetorical action.

Psychopompos: Thoth, Plato’s Phaedrus, and the Context of Egyptian Mythic Rhetoric


 In 1193, King Richard I of England was taken captive by the Holy Roman emperor Henry VI. In several letters, the captive Richard’s mother, Eleanor of Aquitaine, exhorted Pope Celestine III to intercede on her son’s behalf. The specific topics on which she drew were ancient concepts within the topic of honestas, or virtue, and, more specifically, justice as one of the virtues. Justice occupied a preeminent place among the other virtues in medieval thought, and topics related to justice, as a species of honestas, were traditionally regarded as proper for deliberative argumentation. Eleanor’s letters set forth an argumentative schema regarding the nature of justice, asserting that it possesses an anatomy of subordinate parts that include friendship, pity, and the body politic of the kingdom. Her appeals illustrate the significance of ancient virtue theory in medieval political persuasion as an inheritance of Ciceronian thought, the place of virtue in geopolitical civic persuasion in her day, and how women implemented and conceived of social justice from classical rhetorical sources and employed them for civic ends.

Shaun D. Ramsey

Papers

Ray Bilinear Patch Intersections

Adaptive temporal tone mapping

Simplification of Arbitrary Polyhedral Meshes

Psychopompos: Thoth, Plato’s Phaedrus, and the Context of Egyptian Mythic Rhetoric

Honestas and the Angevin Queen: Eleanor of Aquitaine’s Letters and Their Classical Rhetorical Antecedents