30-Issue 8

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https://diglib.eg.org/handle/10.2312/168

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Pre‐computed Gathering of Multi‐Bounce Glossy Reflections
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Laurijssen, Jurgen; Wang, Rui; Lagae, Ares; Dutré, Philip; Eduard Groeller and Holly Rushmeier
Recent work in interactive global illumination addresses diffuse and moderately glossy indirect lighting effects, but high‐frequency effects such as multi‐bounce reflections on highly glossy surfaces are often ignored. Accurately simulating such effects is important to convey the realistic appearance of materials such as chrome and shiny metal. In this paper, we present an efficient method for visualizing multi‐bounce glossy reflections at interactive rates under environment lighting. Our main contribution is a pre‐computation–based method which efficiently gathers subsequent highly glossy reflection passes modelled with a non‐linear transfer function representation based on the von Mises–Fisher distribution. We show that our gathering method is superior to scattered sampling. To exploit the sparsity of the pre‐computed data, we apply perfect spatial hashing. As a result, we are able to visualize multi‐bounce glossy reflections at interactive rates at a low pre‐computation cost.
A General BRDF Representation Based on Tensor Decomposition
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Bilgili, Ahmet; Öztürk, Aydn; Kurt, Murat; Eduard Groeller and Holly Rushmeier
Generating photo‐realistic images through Monte Carlo rendering requires efficient representation of light–surface interaction and techniques for importance sampling. Various models with good representation abilities have been developed but only a few of them have their importance sampling procedure. In this paper, we propose a method which provides a good bidirectional reflectance distribution function (BRDF) representation and efficient importance sampling procedure. Our method is based on representing BRDF as a function of tensor products. Four‐dimensional measured BRDF tensor data are factorized using Tucker decomposition. A large data set is used for comparing the proposed BRDF model with a number of well‐known BRDF models. It is shown that the underlying model provides good approximation to BRDFs.
A New QEM for Parametrization of Raster Images
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Yin, Xuetao; Femiani, John; Wonka, Peter; Razdan, Anshuman; Eduard Groeller and Holly Rushmeier
We present an image processing method that converts a raster image to a simplical two‐complex which has only a small number of vertices (base mesh) plus a parametrization that maps each pixel in the original image to a combination of the barycentric coordinates of the triangle it is finally mapped into. Such a conversion of a raster image into a base mesh plus parametrization can be useful for many applications such as segmentation, image retargeting, multi‐resolution editing with arbitrary topologies, edge preserving smoothing, compression, etc. The goal of the algorithm is to produce a base mesh such that it has a small colour distortion as well as high shape fairness, and a parametrization that is globally continuous visually and numerically. Inspired by multi‐resolution adaptive parametrization of surfaces and quadric error metric, the algorithm converts pixels in the image to a dense triangle mesh and performs error‐bounded simplification jointly considering geometry and colour. The eliminated vertices are projected to an existing face. The implementation is iterative and stops when it reaches a prescribed error threshold. The algorithm is feature‐sensitive, i.e. salient feature edges in the images are preserved where possible and it takes colour into account thereby producing a better quality triangulation.
Reviewers
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Eduard Groeller and Holly Rushmeier
Visualisation Techniques for Using Spatial Augmented Reality in the Design Process of a Car
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Menk, Christoffer; Jundt, Eduard; Koch, Reinhard; Eduard Groeller and Holly Rushmeier
If spatial augmented reality is used in the design process of a car, then one of the most important issues is that the virtual content is projected with a very high visual quality onto the real object, because based on this projection design decisions are made. Especially, the visualised colours on the real object should not be distinguishable from corresponding real reference colours. In this paper, we introduce a new approach for the augmentation of real objects which is able to match the requirements of a design process. We present a new rendering method with ray tracing which increases the visual quality of the projection images in comparison to existing methods. The desired values of these images have further to be adjusted according to the material, the ambient light and the local orientation of the projector. For this purpose, we develop a physically based computation which exactly determines the corresponding projection intensities for these values by using three‐dimensional lookup tables at every projector pixel. Since not all of the desired values can be represented with an intensity of the projector, an adjustment has to be computed for these values. Therefore, we conduct a user study with design experts who work in the automotive industry and use the results to propose a new adjustment method for such values. Finally, we compare our methods to existing procedures and conclude which ones are suitable for the design process of a car.
Learning Boundary Edges for 3D‐Mesh Segmentation
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Benhabiles, Halim; Lavoué, Guillaume; Vandeborre, Jean‐Philippe; Daoudi, Mohamed; Eduard Groeller and Holly Rushmeier
This paper presents a 3D‐mesh segmentation algorithm based on a learning approach. A large database of manually segmented 3D‐meshes is used to learn a boundary edge function. The function is learned using a classifier which automatically selects from a pool of geometric features the most relevant ones to detect candidate boundary edges. We propose a processing pipeline that produces smooth closed boundaries using this edge function. This pipeline successively selects a set of candidate boundary contours, closes them and optimizes them using a snake movement. Our algorithm was evaluated quantitatively using two different segmentation benchmarks and was shown to outperform most recent algorithms from the state‐of‐the‐art.
A Flexible Approach for Output‐Sensitive Rendering of Animated Characters
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Beacco, A.; Spanlang, B.; Andujar, C.; Pelechano, N.; Eduard Groeller and Holly Rushmeier
Rendering detailed animated characters is a major limiting factor in crowd simulation. In this paper we present a new representation for 3D animated characters which supports output‐sensitive rendering. Our approach is flexible in the sense that it does not require us to pre‐define the animation sequences beforehand, nor to pre‐compute a dense set of pre‐rendered views for each animation frame. Each character is encoded through a small collection of textured boxes storing colour and depth values. At runtime, each box is animated according to the rigid transformation of its associated bone and a fragment shader is used to recover the original geometry using a dual‐depth version of relief mapping. Unlike competing output‐sensitive approaches, our compact representation is able to recover high‐frequency surface details and reproduces view‐motion parallax effectively. Our approach drastically reduces both the number of primitives being drawn and the number of bones influencing each primitive, at the expense of a very slight per‐fragment overhead. We show that, beyond a certain distance threshold, our compact representation is much faster to render than traditional level‐of‐detail triangle meshes. Our user study demonstrates that replacing polygonal geometry by our impostors produces negligible visual artefacts.
Table of Contents
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Eduard Groeller and Holly Rushmeier
Stroke Correspondence Construction Using Manifold Learning
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Liu, Dongquan; Chen, Quan; Yu, Jun; Gu, Huiqin; Tao, Dacheng; Seah, Hock Soon; Eduard Groeller and Holly Rushmeier
Stroke correspondence construction is a precondition for generating inbetween frames from a set of key frames. In our case, each stroke in a key frame is a vector represented as a Disk B‐Spline Curve (DBSC) which is a flexible and compact vector format. However, it is not easy to construct correspondences between multiple DBSC strokes effectively because of the following points: (1) with the use of shape descriptors, the dimensionality of the feature space is high; (2) the number of strokes in different key frames is usually large and different from each other and (3) the length of corresponding strokes can be very different. The first point makes matching difficult. The other two points imply ‘many to many’ and ‘part to whole’ correspondences between strokes. To solve these problems, this paper presents a DBSC stroke correspondence construction approach, which introduces a manifold learning technique to the matching process. Moreover, in order to handle the mapping between unequal numbers of strokes with different lengths, a stroke reconstruction algorithm is developed to convert the ‘many to many’ and ‘part to whole’ stroke correspondences to ‘one to one’ compound stroke correspondence.
Visualizing Strain Anisotropy in Mantle Flow Fields
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Obermaier, H.; Billen, M. I.; Hagen, H.; Hering‐Bertram, M.; Hamann, B.; Eduard Groeller and Holly Rushmeier
The evolution of strain and development of material anisotropy in models of the Earth’s mantle flow convey important information about how to interpret the geometric relationship between observation of seismic anisotropy and the actual mantle flow field. By combining feature extraction techniques such as path line integration and tensor accumulation, we compute time‐varying strain vector fields that build the foundation for a number of feature extraction and visualization techniques. The proposed field segmentation, clustering, histograms and multi‐volume visualization techniques facilitate an intuitive understanding of three‐dimensional strain in such flow fields, overcoming limitations of previous methods such as 2‐D line plots and slicing. We present applications of our approach to an artificial time varying flow data set and a real world example of stationary flow in a subduction zone and discuss the challenges of processing these geophysical data sets as well as the insights gained.
Context‐Based Coding of Adaptive Multiresolution Meshes
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Tycowicz, Christoph von; Kälberer, Felix; Polthier, Konrad; Eduard Groeller and Holly Rushmeier
Multiresolution meshes provide an efficient and structured representation of geometric objects. To increase the mesh resolution only at vital parts of the object, adaptive refinement is widely used. We propose a lossless compression scheme for these adaptive structures that exploits the parent–child relationships inherent to the mesh hierarchy. We use the rules that correspond to the adaptive refinement scheme and store bits only where some freedom of choice is left, leading to compact codes that are free of redundancy. Moreover, we extend the coder to sequences of meshes with varying refinement. The connectivity compression ratio of our method exceeds that of state‐of‐the‐art coders by a factor of 2–7. For efficient compression of vertex positions we adapt popular wavelet‐based coding schemes to the adaptive triangular and quadrangular cases to demonstrate the compatibility with our method. Akin to state‐of‐the‐art coders, we use a zerotree to encode the resulting coefficients. Using improved context modelling we enhanced the zerotree compression, cutting the overall geometry data rate by 7% below those of the successful Progressive Geometry Compression. More importantly, by exploiting the existing refinement structure we achieve compression factors that are four times greater than those of coders which can handle irregular meshes.
Finding Syntactic Structures from Human Motion Data
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Park, Jong Pil; Lee, Kang Hoon; Lee, Jehee; Eduard Groeller and Holly Rushmeier
We present a new approach to motion rearrangement that preserves the syntactic structures of an input motion automatically by learning a context‐free grammar from the motion data. For grammatical analysis, we reduce an input motion into a string of terminal symbols by segmenting the motion into a series of subsequences, and then associating a group of similar subsequences with the same symbol. To obtain the most repetitive and precise set of terminals, we search for an optimial segmentation such that a large number of subsequences can be clustered into groups with little error. Once the input motion has been encoded as a string, a grammar induction algorithm is employed to build up a context‐free grammar so that the grammar can reconstruct the original string accurately as well as generate novel strings sharing their syntactic structures with the original string. Given any new strings from the learned grammar, it is straightforward to synthesize motion sequences by replacing each terminal symbol with its associated motion segment, and stitching every motion segment sequentially. We demonstrate the usefulness and flexibility of our approach by learning grammars from a large diversity of human motions, and reproducing their syntactic structures in new motion sequences.
Computational Plenoptic Imaging
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Wetzstein, Gordon; Ihrke, Ivo; Lanman, Douglas; Heidrich, Wolfgang; Eduard Groeller and Holly Rushmeier
The plenoptic function is a ray‐based model for light that includes the colour spectrum as well as spatial, temporal and directional variation. Although digital light sensors have greatly evolved in the last years, one fundamental limitation remains: all standard CCD and CMOS sensors integrate over the dimensions of the plenoptic function as they convert photons into electrons; in the process, all visual information is irreversibly lost, except for a two‐dimensional, spatially varying subset—the common photograph. In this state‐of‐the‐art report, we review approaches that optically encode the dimensions of the plenoptic function transcending those captured by traditional photography and reconstruct the recorded information computationally.
Computational Aesthetics 2011 in Vancouver, Canada, August 5–7, 2011, Sponsored by Eurographics, in Collaboration with ACM SIGGRAPH
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Isenberg, Tobias; Cunningham, Douglas; Eduard Groeller and Holly Rushmeier
An Optimal Control Approach for Texture Metamorphosis
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Kabul, Ilknur; Pizer, Stephen M.; Rosenman, Julian; Niethammer, Marc; Eduard Groeller and Holly Rushmeier
In this paper, we introduce a new texture metamorphosis approach for interpolating texture samples from a source texture into a target texture. We use a new energy optimization scheme derived from optimal control principles which exploits the structure of the metamorphosis optimality conditions. Our approach considers the change in pixel position and pixel appearance in a single framework. In contrast to previous techniques that compute a global warping based on feature masks of textures, our approach allows to transform one texture into another by considering both intensity values and structural features of textures simultaneously. We demonstrate the usefulness of our approach for different textures, such as stochastic, semi‐structural and regular textures, with different levels of complexities. Our method produces visually appealing transformation sequences with no user interaction.
Making Imperfect Shadow Maps View‐Adaptive: High‐Quality Global Illumination in Large Dynamic Scenes
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Ritschel, Tobias; Eisemann, Elmar; Ha, Inwoo; Kim, James D. K.; Seidel, Hans‐Peter; Eduard Groeller and Holly Rushmeier
We propose an algorithm to compute interactive indirect illumination in dynamic scenes containing millions of triangles. It makes use of virtual point lights (VPL) to compute bounced illumination and a point‐based scene representation to query indirect visibility, similar to Imperfect Shadow Maps (ISM). To ensure a high fidelity of indirect light and shadows, our solution is made view‐adaptive by means of two orthogonal improvements: First, the VPL distribution is chosen to provide more detail, that is, more dense VPL sampling, where these contribute most to the current view. Second, the scene representation for indirect visibility is adapted to ensure geometric detail where it affects indirect shadows in the current view.
Simplex and Diamond Hierarchies: Models and Applications
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Weiss, K.; Floriani, L. De; Eduard Groeller and Holly Rushmeier
Hierarchical spatial decompositions are a basic modelling tool in a variety of application domains. Several papers on this subject deal with hierarchical simplicial decompositions generated through regular simplex bisection. Such decompositions, originally developed for finite elements, are extensively used as the basis for multi‐resolution models of scalar fields, such as terrains, and static or time‐varying volume data. They have also been used as an alternative to quadtrees and octrees as spatial access structures. The primary distinction among all such approaches is whether they treat the simplex or clusters of simplices, called diamonds, as the modelling primitive. This leads to two classes of data structures and to different query approaches. We present the hierarchical models in a dimension‐independent manner, and organize the description of the various applications, primarily interactive terrain rendering and isosurface extraction, according to the dimension of the domain.
32nd EUROGRAPHICS General Assembly
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Eduard Groeller and Holly Rushmeier
Perceptually Based Appearance Modification for Compliant Appearance Editing
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Law, Alvin J.; Aliaga, Daniel G.; Sajadi, Behzad; Majumder, Aditi; Pizlo, Zygmunt; Eduard Groeller and Holly Rushmeier
Projection‐based appearances are used in a variety of computer graphics applications to impart different appearances onto physical surfaces using digitally controlled projector light. To achieve a compliant appearance, all points on the physical surface must be altered to the colours of the desired target appearance; otherwise, an incompliant appearance results in a misleading visualization. Previous systems typically assume to operate with compliant appearances or restrict themselves to the simpler case of white surfaces. To achieve compliancy, one may change the physical surface's albedo, increase the amount of projector light radiance available or modify the target appearance's colours. This paper presents an approach to modify a target appearance to achieve compliant appearance editing without altering the physical surface or the projector setup. Our system minimally alters the target appearance's colours while maintaining cues important for perceptual similarity (e.g. colour constancy). First, we discuss how to measure colour compliancy. Next, we describe our approach to partition the physical surface into patches based on the surface's colours and the target appearance's colours. Finally, we describe our appearance optimization process, which computes a compliant appearance that is as perceptually similar as possible to the target appearance's colours. We perform several real‐world projection‐based appearances and compare our results to naïve approaches, which either ignore compliancy or simply reduce the appearance's overall brightness.
Convolution‐Based Simulation of Homogeneous Subsurface Scattering
(The Eurographics Association and Blackwell Publishing Ltd., 2011) Munoz, Adolfo; Echevarria, Jose I.; Seron, Francisco J.; Gutierrez, Diego; Eduard Groeller and Holly Rushmeier
This paper introduces a new method for simulating homogeneous subsurface light transport in translucent objects. Our approach is based on irradiance convolutions over a multi‐layered representation of the volume for light transport, which is general enough to obtain plausible depictions of translucent objects based on the diffusion approximation. We aim at providing an efficient physically based algorithm that can apply arbitrary diffusion profiles to general geometries. We obtain accurate results for a wide range of materials, on par with the hierarchical method by Jensen and Buhler.

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