32-Issue 2

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https://diglib.eg.org/handle/10.2312/180

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Coupled Quasi-harmonic Bases
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Kovnatsky, Artiom; Bronstein, Michael M.; Bronstein, Alexander M.; Glashoff, Klaus; Kimmel, Ron; I. Navazo, P. Poulin
The use of Laplacian eigenbases has been shown to be fruitful in many computer graphics applications. Today, state-of-the-art approaches to shape analysis, synthesis, and correspondence rely on these natural harmonic bases that allow using classical tools from harmonic analysis on manifolds. However, many applications involving multiple shapes are obstacled by the fact that Laplacian eigenbases computed independently on different shapes are often incompatible with each other. In this paper, we propose the construction of common approximate eigenbases for multiple shapes using approximate joint diagonalization algorithms, taking as input a set of corresponding functions (e.g. indicator functions of stable regions) on the two shapes. We illustrate the benefits of the proposed approach on tasks from shape editing, pose transfer, correspondence, and similarity.
Stochastic Depth Buffer Compression using Generalized Plane Encoding
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Andersson, Magnus; Munkberg, Jacob; Akenine-Möller, Tomas; I. Navazo, P. Poulin
In this paper, we derive compact representations of the depth function for a triangle undergoing motion or defocus blur. Unlike a static primitive, where the depth function is planar, the depth function is a rational function in time and the lens parameters. Furthermore, we show how these compact depth functions can be used to design an efficient depth buffer compressor/decompressor, which significantly lowers total depth buffer bandwidth usage for a range of test scenes. In addition, our compressor/decompressor is simpler in the number of operations needed to execute, which makes our algorithm more amenable for hardware implementation than previous methods
Mutable Elastic Models for Sculpting Structured Shapes
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Milliez, Antoine; Wand, Michael; Cani, Marie-Paule; Seidel, Hans-Peter; I. Navazo, P. Poulin
In this paper, we propose a new paradigm for free-form shape deformation. Standard deformable models minimize an energy measuring the distance to a single target shape. We propose a new, ''mutable'' elastic model. It represents complex geometry by a collection of parts and measures the distance of each part measures to a larger set of alternative rest configurations. By detecting and reacting to local switches between best-matching rest states, we build a 3D sculpting system: It takes a structured shape consisting of parts and replacement rules as input. The shape can subsequently be elongated, compressed, bent, cut, and merged within a constraints-based free-form editing interface, where alternative rest-states model to such changes. In practical experiments, we show that the approach yields a surprisingly intuitive and easy to implement interface for interactively designing objects described by such discrete shape grammars, for which direct shape control mechanisms were typically lacking.
Material Editing in Complex Scenes by Surface Light Field Manipulation and Reflectance Optimization
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Nguyen, Chuong H.; Scherzer, Daniel; Ritschel, Tobias; Seidel, Hans-Peter; I. Navazo, P. Poulin
This work addresses the challenge of intuitive appearance editing in scenes with complex geometric layout and complex, spatially-varying indirect lighting. In contrast to previous work, that aimed to edit surface reflectance, our system allows a user to freely manipulate the surface light field. It then finds the best surface reflectance that ''explains'' the surface light field manipulation. Instead of classic L2 fitting of reflectance to a combination of incoming and exitant illumination, our system infers a sparse L0 change of shading parameters instead. Consequently, our system does not require ''diffuse'' or ''glossiness'' brushes or any such understanding of the underlying reflectance parametrization. Instead, it infers reflectance changes from scribbles made by a single simple color brush tool alone: Drawing a highlight will increase Phong specular; blurring a mirror reflection will decrease glossiness; etc. A sparse-solver framework operating on a novel point-based, pre-convolved lighting representation in combination with screen-space edit upsampling allows to perform editing interactively on a GPU.
Primitive Trees for Precomputed Distance Queries
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Lee, Sung-Ho; Park, Taejung; Kim, Chang-Hun; I. Navazo, P. Poulin
We propose the primitive tree, a novel and compact space-partition method that samples and reconstructs a distance field with high accuracy, even for regions far from the surfaces. The primitive tree is based on the octree and stores the indices of the nearest primitives in its leaf nodes. Most previous approaches have involved a trade-off between accuracy and speed in distance queries, but our method can improve both aspects simultaneously. In addition, our method can sample unsigned distance fields effectively, even for self-intersecting and nonmanifold models. We present test results showing that our method can sample and represent large scenes, with more than ten million triangles, rapidly and accurately.
Computing and Fabricating Multiplanar Models
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Chen, Desai; Sitthi-amorn, Pitchaya; Lan, Justin T.; Matusik, Wojciech; I. Navazo, P. Poulin
We present a method for converting computer 3D models into physical equivalents. More specifically, we address the problem of approximating a 3D textured mesh using a small number of planar polygonal primitives that form a closed surface. This simplified representation allows us to easily manufacture individual components using computer controlled cutters (e.g., laser cutters or CNC machines). These polygonal pieces can be assembled into the final 3D model using internal planar connectors that are manufactured simultaneously. Our shape approximation algorithm iteratively assigns mesh faces to planar segments and slowly deforms these faces towards corresponding segments. This approach ensures that the output for a given closed mesh is still a closed mesh and avoids introducing self-intersections. After this step we also compute the shape of polygonal connectors that internally hold the whole mesh surface. Both the polygonal surface elements and connectors can be manufactured in a single cutting pass. We validate the use of our method by computing and manufacturing a variety of textured polyhedral models.
Example-based Interpolation and Synthesis of Bidirectional Texture Functions
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Ruiters, Roland; Schwartz, Christopher; Klein, Reinhard; I. Navazo, P. Poulin
Bidirectional Texture Functions (BTF) have proven to be a well-suited representation for the reproduction of measured real-world surface appearance and provide a high degree of realism. We present an approach for designing novel materials by interpolating between several measured BTFs. For this purpose, we transfer concepts from existing texture interpolation methods to the much more complex case of material interpolation. We employ a separation of the BTF into a heightmap and a parallax compensated BTF to cope with problems induced by parallax, masking and shadowing within the material. By working only on the factorized representation of the parallax compensated BTF and the heightmap, it is possible to efficiently perform the material interpolation. By this novel method to mix existing BTFs, we are able to design plausible and realistic intermediate materials for a large range of different opaque material classes. Furthermore, it allows for the synthesis of tileable and seamless BTFs and finally even the generation of gradually changing materials following user specified material distribution maps.
Analytic Rasterization of Curves with Polynomial Filters
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Manson, Josiah; Schaefer, Scott; I. Navazo, P. Poulin
We present a method of analytically rasterizing shapes that have curved boundaries and linear color gradients using piecewise polynomial prefilters. By transforming the convolution of filters with the image from an integral over area into a boundary integral, we find closed-form expressions for rasterizing shapes. We show that a polynomial expression can be used to rasterize any combination of polynomial curves and filters. Our rasterizer also handles rational quadratic boundaries, which allows us to evaluate circles and ellipses. We apply our technique to rasterizing vector graphics and show that our derivation gives an efficient implementation as a scanline rasterizer.
Sparse Modeling of Intrinsic Correspondences
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Pokrass, Jonathan; Bronstein, Alexander M.; Bronstein, Michael M.; Sprechmann, Pablo; Sapiro, Guillermo; I. Navazo, P. Poulin
We present a novel sparse modeling approach to non-rigid shape matching using only the ability to detect repeatable regions. As the input to our algorithm, we are given only two sets of regions in two shapes; no descriptors are provided so the correspondence between the regions is not know, nor we know how many regions correspond in the two shapes. We show that even with such scarce information, it is possible to establish very accurate correspondence between the shapes by using methods from the field of sparse modeling, being this, the first non-trivial use of sparse models in shape correspondence. We formulate the problem of permuted sparse coding, in which we solve simultaneously for an unknown permutation ordering the regions on two shapes and for an unknown correspondence in functional representation. We also propose a robust variant capable of handling incomplete matches. Numerically, the problem is solved efficiently by alternating the solution of a linear assignment and a sparse coding problem. The proposed methods are evaluated qualitatively and quantitatively on standard benchmarks containing both synthetic and scanned objects.
Animal Locomotion Controllers From Scratch
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Wampler, Kevin; Popovic, Jovan; Popovic, Zoran; I. Navazo, P. Poulin
There exists a large body of research devoted to creating real time interactive locomotion controllers which are targeted at some specific class of character, most often humanoid bipeds. Relatively little work, however, has been done on approaches which are applicable to creatures with a wide range of different forms - partially due to the lack of easily obtainable motion-capture data for animals and fictional creatures. We show how a locomotion controller can be created despite this dearth of data by synthesizing it from scratch. Our method only requires as input a description of the shape of the animal, the gaits which it can perform, and a model of the task or tasks for which the controller will be used. From this a sequence of motion clips are automatically synthesized and assembled into a motion graph which defines a physically realistic controller capable of performing the specified tasks. The method attempts to minimize the computational time required to generate this controller and we show its effectiveness at creating interactive controllers for a range of tasks for bipeds, tripeds, and quadrupeds.
Removing the Noise in Monte Carlo Rendering with General Image Denoising Algorithms
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Kalantari, Nima Khademi; Sen, Pradeep; I. Navazo, P. Poulin
Monte Carlo rendering systems can produce important visual effects such as depth of field, motion blur, and area lighting, but the rendered images suffer from objectionable noise at low sampling rates. Although years of research in image processing has produced powerful denoising algorithms, most of them assume that the noise is spatially-invariant over the entire image and cannot be directly applied to denoise Monte Carlo rendering. In this paper, we propose a new approach that enables the use of any spatially-invariant image denoising technique to remove the noise in Monte Carlo renderings. Our key insight is to use a noise estimation metric to locally identify the amount of noise in different parts of the image, coupled with a multilevel algorithm that denoises the image in a spatially-varying manner using a standard denoising technique. We also propose a new way to perform adaptive sampling that uses the noise estimation metric to identify the noisy regions in which to place more samples. We show that our framework runs in a few seconds with modern denoising algorithms and produces results that outperform state-of-the-art techniques in Monte Carlo rendering.
Bilateral Hermite Radial Basis Functions for Contour-based Volume Segmentation
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Ijiri, Takashi; Yoshizawa, Shin; Sato, Yu; Ito, Masaaki; Yokota, Hideo; I. Navazo, P. Poulin
In this paper, we propose a novel contour-based volume image segmentation technique. Our technique is based on an implicit surface reconstruction strategy, whereby a signed scalar field is generated from user-specified contours. The key idea is to compute the scalar field in a joint spatial-range domain (i.e., bilateral domain) and resample its values on an image manifold. We introduce a new formulation of Hermite radial basis function (HRBF) interpolation to obtain the scalar field in the bilateral domain. In contrast to previous implicit methods, bilateral HRBF (BHRBF) generates a segmentation boundary that passes through all contours, fits high-contrast image edges if they exist, and has a smooth shape in blurred areas of images. We also propose an acceleration scheme for computing B-HRBF to support a real-time and intuitive segmentation interface. In our experiments, we achieved high-quality segmentation results for regions of interest with high-contrast edges and blurred boundaries.
Analytic Visibility on the GPU
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Auzinger, Thomas; Wimmer, Michael; Jeschke, Stefan; I. Navazo, P. Poulin
This paper presents a parallel, implementation-friendly analytic visibility method for triangular meshes. Together with an analytic filter convolution, it allows for a fully analytic solution to anti-aliased 3D mesh rendering on parallel hardware. Building on recent works in computational geometry, we present a new edge-triangle intersection algorithm and a novel method to complete the boundaries of all visible triangle regions after a hidden line elimination step. All stages of the method are embarrassingly parallel and easily implementable on parallel hardware. A GPU implementation is discussed and performance characteristics of the method are shown and compared to traditional sampling-based rendering methods.
DuctTake: Spatiotemporal Video Compositing
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Rüegg, Jan; Wang, Oliver; Smolic, Aljoscha; Gross, Markus; I. Navazo, P. Poulin
DuctTake is a system designed to enable practical compositing of multiple takes of a scene into a single video. Current industry solutions are based around object segmentation, a hard problem that requires extensive manual input and cleanup, making compositing an expensive part of the film-making process. Our method instead composites shots together by finding optimal spatiotemporal seams using motion-compensated 3D graph cuts through the video volume. We describe in detail the required components, decisions, and new techniques that together make a usable, interactive tool for compositing HD video, paying special attention to running time and performance of each section. We validate our approach by presenting a wide variety of examples and by comparing result quality and creation time to composites made by professional artists using current state-of-the-art tools.
Freeform Shadow Boundary Editing
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Mattausch, Oliver; Igarashi, Takeo; Wimmer, Michael; I. Navazo, P. Poulin
We present an algorithm for artistically modifying physically based shadows. With our tool, an artist can directly edit the shadow boundaries in the scene in an intuitive fashion similar to freeform curve editing. Our algorithm then makes these shadow edits consistent with respect to varying light directions and scene configurations, by creating a shadow mesh from the new silhouettes. The shadow mesh helps a modified shadow volume algorithm cast shadows that conform to the artistic shadow boundary edits, while providing plausible interaction with dynamic environments, including animation of both characters and light sources. Our algorithm provides significantly more fine-grained local and direct control than previous artistic light editing methods, which makes it simple to adjust the shadows in a scene to reach a particular effect, or to create interesting shadow shapes and shadow animations. All cases are handled with a single intuitive interface, be it soft shadows, or (self-)shadows on arbitrary receivers.
Scalable Music: Automatic Music Retargeting and Synthesis
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Wenner, Simon; Bazin, Jean-Charles; Sorkine-Hornung, Alexander; Kim, Changil; Gross, Markus; I. Navazo, P. Poulin
In this paper we propose a method for dynamic rescaling of music, inspired by recent works on image retargeting, video reshuffling and character animation in the computer graphics community. Given the desired target length of a piece of music and optional additional constraints such as position and importance of certain parts, we build on concepts from seam carving, video textures and motion graphs and extend them to allow for a global optimization of jumps in an audio signal. Based on an automatic feature extraction and spectral clustering for segmentation, we employ length-constrained least-costly path search via dynamic programming to synthesize a novel piece of music that best fulfills all desired constraints, with imperceptible transitions between reshuffled parts. We show various applications of music retargeting such as part removal, decreasing or increasing music duration, and in particular consistent joint video and audio editing.
Interactive Exploration and Flattening of Deformed Historical Documents
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Pal, Kazim; Terras, Melissa; Weyrich, Tim; I. Navazo, P. Poulin
We present an interactive application for browsing severely damaged documents and other cultural artefacts. Such documents often contain strong geometric distortions such as wrinkling, buckling, and shrinking and cannot be flattened physically due to the high risk of causing further damage. Previous methods for virtual restoration involve globally flattening a 3D reconstruction of the document to produce a static image. We show how this global approach can fail in cases of severe geometric distortion, and instead propose an interactive viewer which allows a user to browse a document while dynamically flattening only the local region under inspection. Our application also records the provenance of the reconstruction by displaying the reconstruction side by side with the original image data.
Fleshing: Spine-driven Bending with Local Volume Preservation
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Zhuo, Wei; Rossignac, Jarek; I. Navazo, P. Poulin
Several design and animation techniques use a one-dimensional proxyC (a spine curve in 3D) to control the deformation or behavior of a digital model of a 3D shape S. We propose a modification of these ''skinning'' techniques that ensures local volume preservation, which is important for the physical plausibility of digital simulations. In the proposed ''fleshing'' techniques, as input, we consider a smooth spine C0, a model S0 of a solid that lies ''sufficiently close'' to C0, and a deformed version C1 of C0 that is ''not overly bent''. (We provide a precise characterization of these restrictions.) As output, we produce a bijective mapping M, that maps any point X of S onto a point M(X) of M(S). M satisfies two properties: (1) The closest projection of X on C0 and of M(X) on C1 have the same arc length parameter. (2) U and M(U) have the same volume, where U is any subset of S. We provide three different closed form expressions for radial, normal and binormal fleshing and discuss the details of their practical real-time implementation.
Interactive Facades - Analysis and Synthesis of Semi-Regular Facades
(The Eurographics Association and Blackwell Publishing Ltd., 2013) AlHalawani, Sawsan; Yang, Yong-Liang; Liu, Han; Mitra, Niloy J.; I. Navazo, P. Poulin
Urban facades regularly contain interesting variations due to allowed deformations of repeated elements (e.g., windows in different open or close positions) posing challenges to state-of-the-art facade analysis algorithms. We propose a semi-automatic framework to recover both repetition patterns of the elements and their individual deformation parameters to produce a factored facade representation. Such a representation enables a range of applications including interactive facade images, improved multi-view stereo reconstruction, facade-level change detection, and novel image editing possibilities.
Exploring Local Modifications for Constrained Meshes
(The Eurographics Association and Blackwell Publishing Ltd., 2013) Deng, Bailin; Bouaziz, Sofien; Deuss, Mario; Zhang, Juyong; Schwartzburg, Yuliy; Pauly, Mark; I. Navazo, P. Poulin
Mesh editing under constraints is a challenging task with numerous applications in geometric modeling, industrial design, and architectural form finding. Recent methods support constraint-based exploration of meshes with fixed connectivity, but commonly lack local control. Because constraints are often globally coupled, a local modification by the user can have global effects on the surface, making iterative design exploration and refinement difficult. Simply fixing a local region of interest a priori is problematic, as it is not clear in advance which parts of the mesh need to be modified to obtain an aesthetically pleasing solution that satisfies all constraints. We propose a novel framework for exploring local modifications of constrained meshes. Our solution consists of three steps. First, a user specifies target positions for one or more vertices. Our algorithm computes a sparse set of displacement vectors that satisfies the constraints and yields a smooth deformation. Then we build a linear subspace to allow realtime exploration of local variations that satisfy the constraints approximately. Finally, after interactive exploration, the result is optimized to fully satisfy the set of constraints. We evaluate our framework on meshes where each face is constrained to be planar.

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