EGSR06: 17th Eurographics Symposium on Rendering

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https://diglib.eg.org/handle/10.2312/385

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Adaptive Visibility-Driven View Cell Construction
(The Eurographics Association, 2006) Mattausch, Oliver; Bittner, Jirí; Wimmer, Michael; Tomas Akenine-Moeller and Wolfgang Heidrich
We present a new method for the automatic partitioning of view space into a multi-level view cell hierarchy. We use a cost-based model in order to minimize the average rendering time. Unlike previous methods, our model takes into account the actual visibility in the scene, and the partition is not restricted to planes given by the scene geometry. We show that the resulting view cell hierarchy works for different types of scenes and gives lower average rendering time than previously used methods.
Ambient Occlusion for Animated Characters
(The Eurographics Association, 2006) Kontkanen, Janne; Aila, Timo; Tomas Akenine-Moeller and Wolfgang Heidrich
We present a novel technique for approximating ambient occlusion of animated objects. Our method automatically determines the correspondence between animation parameters and per-vertex ambient occlusion using a set of reference poses as its input. Then, at runtime, the ambient occlusion is approximated by taking a dot product between the current animation parameters and static per-vertex coefficients. According to our results, both the computational and storage requirements are low enough for the technique to be directly applicable to computer games running on current graphics hardware. The resulting images are also significantly more realistic than the commonly used static ambient occlusion solutions.
Antialiasing for Automultiscopic 3D Displays
(The Eurographics Association, 2006) Zwicker, Matthias; Matusik, Wojciech; Durand, Frédo; Pfister, Hanspeter; Tomas Akenine-Moeller and Wolfgang Heidrich
Automultiscopic displays show stereoscopic images that can be viewed from any viewpoint without special glasses. They hold great promise for the future of television and digital entertainment. However, the image quality on these 3D displays is currently not sufficient to appeal to the mass market. In this paper, we extend the frequency analysis of light fields to address some of the major issues in 3D cinematography for automultiscopic displays. First, we derive the bandwidth of 3D displays using ray-space analysis, and we introduce a method to quantify display depth of field. We show that this approach provides solid foundations to analyze and distinguish various aspects of aliasing. We then present an anti-aliasing technique for automultiscopic displays by combining a reconstruction and a display prefilter. Next, we show how to reparameterize multi-view inputs to optimally match the depth of field of a display to improve the image quality. Finally, we present guidelines for 3D content acquisition, such as optimal multi-view camera configuration and placement.
Ardeco: Automatic Region DEtection and COnversion
(The Eurographics Association, 2006) Lecot, Gregory; Levy, Bruno; Tomas Akenine-Moeller and Wolfgang Heidrich
We present Ardeco, a new algorithm for image abstraction and conversion from bitmap images into vector graphics. Given a bitmap image, our algorithm automatically computes the set of vector primitives and gradients that best approximates the image. In addition, more details can be generated in user-selected important regions, defined from eye-tracking data or from an importance map painted by the user. Our algorithm is based on a new two-level variational parametric segmentation algorithm, minimizing Mumford and Shah s energy and operating on an intermediate triangulation, well adapted to the features of the image.
Automatic Multiperspective Images
(The Eurographics Association, 2006) Román, Augusto; Lensch, Hendrik P. A.; Tomas Akenine-Moeller and Wolfgang Heidrich
Multiperspective images generated from a collection of photographs or a videostream can be used to effectively summarize long, roughly planar scenes such as city streets. The final image will span a larger field of view than any single input image. However, common projections used to make these images, including cross-slits and pushbroom projections, may suffer from depth-related distortions in non-planar scenes. In this paper, we use an aspect-ratio distortion metric to compare these images to standard perspective projections. By minimizing this error metric we can automatically define the picture surface and viewpoints of a multiperspective image that reduces distortion artifacts. This optimization requires only a coarse estimate of scene geometry which can be provided as a depth map or a 2D spatial importance map defining interesting parts of the scene. These maps can be automatically constructed in most cases, allowing rapid generation of images of very long scenes.
Bidirectional Instant Radiosity
(The Eurographics Association, 2006) Segovia, Benjamin; Iehl, Jean Claude; Mitanchey, Richard; Péroche, Bernard; Tomas Akenine-Moeller and Wolfgang Heidrich
This paper presents a new sampling strategy to achieve interactive global illumination on one commodity computer. The goal is to propose an efficient numerical stochastic scheme which can be well adapted to a fast rendering algorithm. As we want to provide an efficient sampling strategy to handle difficult settings without sacrificing performance in common cases, we developed an extension of Instant Radiosity [Kel97] in the same way bidirectional path tracing is an extension of path or light tracing. Our idea is to build several estimators and to efficiently combine them to find a set of virtual point light sources which are relevant for the areas of the scene seen by the camera. The resulting algorithm is faster than classical solutions to global illumination. Using today graphics hardware, an interactive frame rate and the convergence of the scheme can be easily obtained in scenes with many light sources, glossy materials or difficult visibility problems.
Directing Gaze in 3D Models with Stylized Focus
(The Eurographics Association, 2006) Cole, Forrester; DeCarlo, Doug; Finkelstein, Adam; Kin, Kenrick; Morley, Keith; Santella, Anthony; Tomas Akenine-Moeller and Wolfgang Heidrich
We present an interactive system for placing emphasis in stylized renderings of 3D models. The artist chooses a camera position, an area of interest, and a rendering style for the scene. The system then automatically renders the scene with emphasis in the area of interest, an effect we call "stylized focus." Stylized focus draws the viewer s gaze to the emphasized area, through local variations in shading effects such as color saturation and contrast as well as line qualities such as texture and density. We introduce a novel algorithm for local control of line density that exhibits a degree of temporal coherence suitable for animation. Animating the area of emphasis produces an effect we call the "stylized focus pull." Finally, an eye-tracking experiment verifies that the emphasis does indeed draw the viewer s gaze to the area of interest.
An Efficient Multi-View Rasterization Architecture
(The Eurographics Association, 2006) Hasselgren, Jon; Akenine-Möller, Tomas; Tomas Akenine-Moeller and Wolfgang Heidrich
TV have been designed and built. However, these displays have received relatively little attention in the context of real-time computer graphics. We present a novel rasterization architecture that rasterizes each triangle to multiple views simultaneously. When determining which tile in which view to rasterize next, we use an efficiency measure that estimates which tile is expected to get the most hits in the texture cache. Once that tile has been rasterized, the efficiency measure is updated, and a new tile and view are selected. Our traversal algorithm provides significant reductions in the amount of texture fetches, and bandwidth gains on the order of a magnitude have been observed. We also present an approximate rasterization algorithm that avoids pixel shader evaluations for a substantial amount (up to 95%) of fragments and still maintains high image quality.
Efficient Wavelet Rotation for Environment Map Rendering
(The Eurographics Association, 2006) Wang, Rui; Ng, Ren; Luebke, David; Humphreys, Greg; Tomas Akenine-Moeller and Wolfgang Heidrich
Real-time shading with environment maps requires the ability to rotate the global lighting to each surface point's local coordinate frame. Although extensive previous work has studied rotation of functions represented by spherical harmonics, little work has investigated efficient rotation of wavelets. Wavelets are superior at approximating high frequency signals such as detailed high dynamic range lighting and very shiny BRDFs, but present difficulties for interactive rendering due to the lack of an analytic solution for rotation. In this paper we present an efficient computational solution for wavelet rotation using precomputed matrices. Each matrix represents the linear transformation of source wavelet bases defined in the global coordinate frame to target wavelet bases defined in sampled local frames. Since wavelets have compact support, these matrices are very sparse, enabling efficient storage and fast computation at run-time. In this paper, we focus on the application of our technique to interactive environment map rendering. We show that using these matrices allows us to evaluate the integral of dynamic lighting with dynamic BRDFs at interactive rates, incorporating efficient non-linear approximation of both illumination and reflection. Our technique improves on previous work by eliminating the need for prefiltering environment maps, and is thus significantly faster for accurate rendering of dynamic environment lighting with high frequency reflection effects.
Exploiting Temporal Coherence for Incremental All-Frequency Relighting
(The Eurographics Association, 2006) Overbeck, Ryan; Ben-Artzi, Aner; Ramamoorthi, Ravi; Grinspun, Eitan; Tomas Akenine-Moeller and Wolfgang Heidrich
Precomputed radiance transfer (PRT) enables all-frequency relighting with complex illumination, materials and shadows. To achieve real-time performance, PRT exploits angular coherence in the illumination, and spatial coherence in the light transport. Temporal coherence of the lighting from frame to frame is an important, but unexplored additional form of coherence for PRT. In this paper, we develop incremental methods for approximating the differences in lighting between consecutive frames. We analyze the lighting wavelet decomposition over typical motion sequences, and observe differing degrees of temporal coherence across levels of the wavelet hierarchy. To address this, our algorithm treats each level separately, adapting to available coherence. The proposed method is orthogonal to other forms of coherence, and can be added to almost any all-frequency PRT algorithm with minimal implementation, computation or memory overhead. We demonstrate our technique within existing codes for nonlinear wavelet approximation, changing view with BRDF factorization, and clustered PCA. Exploiting temporal coherence of dynamic lighting yields a 3×-4× performance improvement, e.g., all-frequency effects are achieved with 30 wavelet coefficients per frame for the lighting, about the same as low-frequency spherical harmonic methods. Distinctly, our algorithm smoothly converges to the exact result within a few frames of the lighting becoming static.
Feature-Aware Texturing
(The Eurographics Association, 2006) Gal, Ran; Sorkine, Olga; Cohen-Or, Daniel; Tomas Akenine-Moeller and Wolfgang Heidrich
We present a method for inhomogeneous 2D texture mapping guided by a feature mask, that preserves some regions of the image, such as foreground objects or other prominent parts. The method is able to arbitrarily warp a given image while preserving the shape of its features by constraining their deformation to be a similarity transformation. In particular, our method allows global or local changes to the aspect ratio of the texture without causing undesirable shearing to the features. The algorithmic core of our method is a particular formulation of the Laplacian editing technique, suited to accommodate similarity constraints on parts of the domain. The method is useful in digital imaging, texture design and any other applications involving image warping, where parts of the image have high familiarity and should retain their shape after modification.
A GPU-driven Algorithm for Accurate Interactive Reflections on Curved Objects
(The Eurographics Association, 2006) Estalella, Pau; Martin, Ignacio; Drettakis, George; Tost, Dani; Tomas Akenine-Moeller and Wolfgang Heidrich
We present a GPU-driven method for the fast computation of specular reflections on curved objects. For every reflector of the scene, our method computes a virtual object for every other object reflected in it. This virtual reflected object is then rendered and blended with the scene. For each vertex of each virtual object, a reflection point is found on the reflector s surface. This point is used to find the reflected virtual vertex, enabling the reflected virtual scene to be rendered. Our method renders the 3D points and normals of the reflector into textures, and uses a local search in a fragment program on the GPU to find the reflection points. By reorganizing the data and the computation in this manner, and correctly treating special cases, we make excellent use of the parallelism and stream-processing power of the GPU. In our results we show that, with our method, we can display high-quality reflections of nearby objects interactively.
Handheld Pixels
(The Eurographics Association, 2006) Nordlund, Petri; Tomas Akenine-Moeller and Wolfgang Heidrich
During this decade, pixels have become mobile. Cell phones, PDAs, handheld gaming consoles and other similar devices start to have color displays by standard and color displays are hungry for high-quality graphics. QVGA and VGA display resolutions are common, requiring dedicated hardware for graphics acceleration. Color displays and open platforms also invite games and other applications, which build on the availability of robust graphics. Handheld graphics acceleration is close to its desktop and games console counterparts - with content running on an embedded version of OpenGL, the OpenGL ES 2.0, vertex and pixel shaders are a requirement. Floating-point accuracy, lots of texture surfaces, plenty of performance - handheld pixels are of good quality and there are lots of them. Handheld gaming drives the handheld 3D graphics performance, but unlike on desktops, vector graphics hardware acceleration will become an even widely spread requirement on new handheld platforms. Applications such as the device's main graphical user interface and interactive maps are driving these requirements. In addition to performance, a strong driver for vector graphics on handhelds is image quality. The first handheld devices, including cell phones, with dedicated 3D graphics accelerators have already hit the market. By 2010, a large number of new cell phones and PDAs will be enabled with hardware vector- and 3D graphics acceleration. The volume of graphics acceleration enabled silicon chips shipping for handheld devices is expected to be significantly higher than for desktop PCs and gaming consoles. This creates a lucrative platform for game and application developers who want to develop handheld content with high-quality graphics. As there are numerous different handheld devices, the industry is fighting against fragmentation - widely adopted platforms must be created to enable universal content development across a wide range of platforms and end devices - the platform race is already on. All in all, the industry is busy creating all the essential components to bring high-quality programmable pixels to handheld devices. Content developers are already up-to speed to provide winning content for these devices. All in all, the future of handheld pixels looks rosy!
Image-driven Navigation of Analytical BRDF Models
(The Eurographics Association, 2006) Ngan, Addy; Durand, Frédo; Matusik, Wojciech; Tomas Akenine-Moeller and Wolfgang Heidrich
Specifying parameters of analytic BRDF models is a difficult task as these parameters are often not intuitive for artists and their effect on appearance can be non-uniform. Ideally, a given step in the parameter space should produce a predictable and perceptually-uniform change in the rendered image. Systems that employ psychophysics have produced important advances in this direction; however, the requirement of user studies limits scalability of these approaches. In this work, we propose a new and intuitive method for designing material appearance. First, we define a computational metric between BRDFs that is based on rendered images of a scene under natural illumination. We show that our metric produces results that agree with previous perceptual studies. Next, we propose a user interface that allows for navigation in the remapped parameter space of a given BRDF model. For the current settings of the BRDF parameters, we display a choice of variations corresponding to uniform steps according to our metric, in the various parameter directions. In addition to the parametric navigation for a single model, we also support neighborhood navigation in the space of all models. By clustering a large number of neighbors and removing neighbors that are close to the current model, the user can easily visualize the alternate effects that can only be expressed with other models. We show that our interface is simple and intuitive. Furthermore, visual navigation in the BRDF space both in the local model and the union space is an effective way for reflectance design.
Instant Ray Tracing: The Bounding Interval Hierarchy
(The Eurographics Association, 2006) Wächter, Carsten; Keller, Alexander; Tomas Akenine-Moeller and Wolfgang Heidrich
We introduce a new ray tracing algorithm that exploits the best of previous methods: Similar to bounding volume hierarchies the memory of the acceleration data structure is linear in the number of objects to be ray traced and can be predicted prior to construction, while the traversal of the hierarchy is as efficient as the one of kd-trees. The construction algorithm can be considered a variant of quicksort and for the first time is based on a global space partitioning heuristic, which is much cheaper to evaluate than the classic surface area heuristic. Compared to spatial partitioning schemes only a fraction of the memory is used and a higher numerical precision is intrinsic. The new method is simple to implement and its high performance is demonstrated by extensive measurements including massive as well as dynamic scenes, where we focus on the total time to image including the construction cost rather than on only frames per second.
Interactive Screen-Space Accurate Photon Tracing on GPUs
(The Eurographics Association, 2006) Krüger, Jens; Bürger, Kai; Westermann, Rüdiger; Tomas Akenine-Moeller and Wolfgang Heidrich
Recent advances in algorithms and graphics hardware have opened the possibility to render caustics at interactive rates on commodity PCs. This paper extends on this work in that it presents a new method to directly render caustics on complex objects, to compute one or several refractions at such objects and to simulate caustics shadowing. At the core of our method is the idea to avoid the construction of photon maps by tracing photons in screen-space on programmable graphics hardware. Our algorithm is based on the rasterization of photon paths into texture maps. Intersection events are then resolved on a per-fragment basis using layered depth images. To correctly spread photon energy in screen-space we render aligned point sprites at the diffuse receivers where photons terminate. As our method does neither require any pre-processing nor an intermediate radiance representation it can efficiently deal with dynamic scenery and scenery that is modified, or even created on the GPU.
Making Radiance and Irradiance Caching Practical: Adaptive Caching and Neighbor Clamping
(The Eurographics Association, 2006) Krivánek, Jaroslav; Bouatouch, Kadi; Pattanaik, Sumanta; Zára, Jirí; Tomas Akenine-Moeller and Wolfgang Heidrich
Radiance and irradiance caching are efficient global illumination algorithms based on interpolating indirect illumination from a sparse set of cached values. In this paper we propose an adaptive algorithm for guiding spatial density of the cached values in radiance and irradiance caching. The density is adapted to the rate of change of indirect illumination in order to avoid visible interpolation artifacts and produce smooth interpolated illumination. In addition, we discuss some practical problems arising in the implementation of radiance and irradiance caching, and propose techniques for solving those problems. Namely, the neighbor clamping heuristic is proposed as a robust means for detecting small sources of indirect illumination and for dealing with problems caused by ray leaking through small gaps between adjacent polygons.
Near Optimal Hierarchical Culling: Performance Driven Use of Hardware Occlusion Queries
(The Eurographics Association, 2006) Guthe, Michael; Balázs, Ákos; Klein, Reinhard; Tomas Akenine-Moeller and Wolfgang Heidrich
The most efficient general occlusion culling techniques are based on hardware accelerated occlusion queries. Although in many cases these techniques can considerably improve performance, they may still reduce efficiency compared to simple view frustum culling, especially in the case of low depth complexity. This prevented the broad use of occlusion culling in most commercial applications. In this paper we present a new conservative method to solve this problem, where the main idea is to use a statistical model describing the occlusion probability for each occlusion query in order to reduce the number of wasted queries which are the reason for the reduction in rendering speed. We also describe an abstract parameterized model for the graphics hardware performance. The parameters are easily measurable at startup and thus the model can be adapted to the graphics hardware in use. Combining this model with the estimated occlusion probability our method is able to achieve a near optimal scheduling of the occlusion queries. The implementation of the algorithm is straightforward and it can be easily integrated in existing real-time rendering packages based on common hierarchical data structures.
A Novel Method for Fast and High-Quality Rendering of Hair
(The Eurographics Association, 2006) Xu, Songhua; Lau, Francis C. M.; Jiang, Hao; Pan, Yunhe; Tomas Akenine-Moeller and Wolfgang Heidrich
This paper proposes a new rendering approach for hair. The model we use incorporates semantics-related information directly in the appearance modeling function which we call a Semantics-Aware Texture Function (SATF). This new appearance modeling function is well suited for constructing an off-line/on-line hybrid algorithm to achieve fast and high-quality rendering of hair. The off-line phase generates intermediate results in a database for sample geometries under different viewing and lighting conditions, which can be used to complete a large part of the overall computation and leaves only a few dynamic tasks to be performed on-line. We propose a model having four levels, from the whole hair volume to the very fine hair density level. We further employ an efficient disk-like structure to represent hair distributions inside a hair cluster. As the intermediate database carries opacity information, self-shadows can be easily generated. We present experiment results which clearly show that our methodology can indeed produce high quality rendering results efficiently. Supplementary materials and supporting demos can be found in our project website http://www.cs.hku.hk/~songhua/hair-rendering/.
Painting With Texture
(The Eurographics Association, 2006) Ritter, Lincoln; Li, Wilmot; Curless, Brian; Agrawala, Maneesh; Salesin, David; Tomas Akenine-Moeller and Wolfgang Heidrich
We present an interactive texture painting system that allows the user to author digital images by painting with a palette of input textures. At the core of our system is an interactive texture synthesis algorithm that generates textures with natural-looking boundary effects and alpha information as the user paints. Furthermore, we describe an intuitive layered painting model that allows strokes of texture to be merged, intersected and overlapped while maintaining the appropriate boundaries between texture regions. We demonstrate the utility and expressiveness of our system by painting several images using textures that exhibit a range of different boundary effects.

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