36-Issue 2

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https://diglib.eg.org/handle/10.2312/2631245

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Makeup Lamps: Live Augmentation of Human Faces via Projection
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Bermano, Amit Haim; Billeter, Markus; Iwai, Daisuke; Grundhöfer, Anselm; Loic Barthe and Bedrich Benes
We propose the first system for live dynamic augmentation of human faces. Using projector-based illumination, we alter the appearance of human performers during novel performances. The key challenge of live augmentation is latency - an image is generated according to a specific pose, but is displayed on a different facial configuration by the time it is projected. Therefore, our system aims at reducing latency during every step of the process, from capture, through processing, to projection. Using infrared illumination, an optically and computationally aligned high-speed camera detects facial orientation as well as expression. The estimated expression blendshapes are mapped onto a lower dimensional space, and the facial motion and non-rigid deformation are estimated, smoothed and predicted through adaptive Kalman filtering. Finally, the desired appearance is generated interpolating precomputed offset textures according to time, global position, and expression. We have evaluated our system through an optimized CPU and GPU prototype, and demonstrated successful low latency augmentation for different performers and performances with varying facial play and motion speed. In contrast to existing methods, the presented system is the first method which fully supports dynamic facial projection mapping without the requirement of any physical tracking markers and incorporates facial expressions.
Sparse Inertial Poser: Automatic 3D Human Pose Estimation from Sparse IMUs
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Marcard, Timo von; Rosenhahn, Bodo; Black, Michael J.; Pons-Moll, Gerard; Loic Barthe and Bedrich Benes
We address the problem of making human motion capture in the wild more practical by using a small set of inertial sensors attached to the body. Since the problem is heavily under-constrained, previous methods either use a large number of sensors, which is intrusive, or they require additional video input. We take a different approach and constrain the problem by: (i) making use of a realistic statistical body model that includes anthropometric constraints and (ii) using a joint optimization framework to fit the model to orientation and acceleration measurements over multiple frames. The resulting tracker Sparse Inertial Poser (SIP) enables motion capture using only 6 sensors (attached to the wrists, lower legs, back and head) and works for arbitrary human motions. Experiments on the recently released TNT15 dataset show that, using the same number of sensors, SIP achieves higher accuracy than the dataset baseline without using any video data.We further demonstrate the effectiveness of SIP on newly recorded challenging motions in outdoor scenarios such as climbing or jumping over a wall.
Spatial Adjacency Maps for Translucency Simulation under General Illumination
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Maisch, Sebastian; Ropinski, Timo; Loic Barthe and Bedrich Benes
Rendering translucent materials in real time is usually done by using surface diffusion and/or (translucent) shadow maps. The downsides of these approaches are, that surface diffusion cannot handle translucency effects that show up when rendering thin objects, and that translucent shadow maps are only available for point light sources. Furthermore, translucent shadow maps introduce limitations to shadow mapping techniques exploiting the same maps. In this paper we present a novel approach for rendering translucent materials at interactive frame rates. Our approach allows for an efficient calculation of translucency with native support for general illumination conditions, especially area and environment lighting, at high accuracy. The proposed technique's only parameter is the used diffusion profile, and thus it works out of the box without any parameter tuning. Furthermore, it can be used in combination with any existing surface diffusion techniques to add translucency effects. Our approach introduces Spatial Adjacency Maps that depend on precalculations to be done for fixed meshes. We show that these maps can be updated in real time to also handle deforming meshes and that our results are of superior quality as compared to other well known real-time techniques for rendering translucency.
Texture Stationarization: Turning Photos into Tileable Textures
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Moritz, Joep; James, Stuart; Haines, Tom S. F.; Ritschel, Tobias; Weyrich, Tim; Loic Barthe and Bedrich Benes
Texture synthesis has grown into a mature field in computer graphics, allowing the synthesis of naturalistic textures and images from photographic exemplars. Surprisingly little work, however, has been dedicated to synthesizing tileable textures, that is, textures that when laid out in a regular grid of tiles form a homogeneous appearance suitable for use in memory-sensitive real-time graphics applications. One of the key challenges in doing so is that most natural input exemplars exhibit uneven spatial variations that, when tiled, show as repetitive patterns. We propose an approach to synthesize tileable textures while enforcing stationarity properties that effectively mask repetitions while maintaining the unique characteristics of the exemplar. We explore a number of alternative measures for texture stationarity and show how each measure can be integrated into a standard texture synthesis method (PatchMatch) to enforce stationarity at user-controlled scales. We demonstrate the efficacy of our approach using a database of 118 exemplar images, both from publicly available sources as well as new ones captured under uncontrolled conditions, and we quantitatively analyze alternative stationarity measures for their robustness across many test runs using different random seeds. In conclusion, we suggest a novel synthesis approach that employs local histogram matching to reliably turn input photographs of natural surfaces into tiles well suited for artifact-free tiling.
ShapeGenetics: Using Genetic Algorithms for Procedural Modeling
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Haubenwallner, Karl; Seidel, Hans-Peter; Steinberger, Markus; Loic Barthe and Bedrich Benes
In this paper, we show that genetic algorithms (GA) can be used to control the output of procedural modeling algorithms. We propose an efficient way to encode the choices that have to be made during a procedural generation as a hierarchical genome representation. In combination with mutation and reproduction operations specifically designed for controlled procedural modeling, our GA can evolve a population of individual models close to any high-level goal. Possible scenarios include a volume that should be filled by a procedurally grown tree or a painted silhouette that should be followed by the skyline of a procedurally generated city. These goals are easy to set up for an artist compared to the tens of thousands of variables that describe the generated model and are chosen by the GA. Previous approaches for controlled procedural modeling either use Reversible Jump Markov Chain Monte Carlo (RJMCMC) or Stochastically-Ordered Sequential Monte Carlo (SOSMC) as workhorse for the optimization. While RJMCMC converges slowly, requiring multiple hours for the optimization of larger models, it produces high quality models. SOSMC shows faster convergence under tight time constraints for many models, but can get stuck due to choices made in the early stages of optimization. Our GA shows faster convergence than SOSMC and generates better models than RJMCMC in the long run.
On Realism of Architectural Procedural Models
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Beneš, Jan; Kelly, Tom; Děchtěrenko, Filip; Křivánek, Jaroslav; Müller, Pascal; Loic Barthe and Bedrich Benes
The goal of procedural modeling is to generate realistic content. The realism of this content is typically assessed by qualitatively evaluating a small number of results, or, less frequently, by conducting a user study. However, there is a lack of systematic treatment and understanding of what is considered realistic, both in procedural modeling and for images in general. We conduct a user study that primarily investigates the realism of procedurally generated buildings. Specifically, we investigate the role of fine and coarse details, and investigate which other factors contribute to the perception of realism. We find that realism is carried on different scales, and identify other factors that contribute to the realism of procedural and non-procedural buildings.
Sparse Rig Parameter Optimization for Character Animation
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Song, Jaewon; Ribera, Roger Blanco i; Cho, Kyungmin; You, Mi; Lewis, J. P.; Choi, Byungkuk; Noh, Junyong; Loic Barthe and Bedrich Benes
We propose a novel motion retargeting method that efficiently estimates artist-friendly rig space parameters. Inspired by the workflow typically observed in keyframe animation, our approach transfers a source motion into a production friendly character rig by optimizing the rig space parameters while balancing the considerations of fidelity to the source motion and the ease of subsequent editing. We propose the use of an intermediate object to transfer both the skeletal motion and the mesh deformation. The target rig-space parameters are then optimized to minimize the error between the motion of an intermediate object and the target character. The optimization uses a set of artist defined weights to modulate the effect of the different rig space parameters over time. Sparsity inducing regularizers and keyframe extraction streamline any additional editing processes. The results obtained with different types of character rigs demonstrate the versatility of our method and its effectiveness in simplifying any necessary manual editing within the production pipeline.
Unbiased Light Transport Estimators for Inhomogeneous Participating Media
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Szirmay-Kalos, László; Georgiev, Iliyan; Magdics, Milán; Molnár, Balázs; Légrády, Dávid; Loic Barthe and Bedrich Benes
This paper presents a new stochastic particle model for efficient and unbiased Monte Carlo rendering of heterogeneous participating media. We randomly add and remove material particles to obtain a density with which free flight sampling and transmittance estimation are simple, while material particle properties are simultaneously modified to maintain the true expectation of the radiance. We show that meeting this requirement may need the introduction of light particles with negative energy and materials with negative extinction, and provide an intuitive interpretation for such phenomena. Unlike previous unbiased methods, the proposed approach does not require a-priori knowledge of the maximum medium density that is typically difficult to obtain for procedural models. However, the method can benefit from an approximate knowledge of the density, which can usually be acquired on-the-fly at little extra cost and can greatly reduce the variance of the proposed estimators. The introduced mechanism can be integrated in participating media renderers where transmittance estimation and free flight sampling are building blocks. We demonstrate its application in a multiple scattering particle tracer, in transmittance computation, and in the estimation of the inhomogeneous air-light integral.
Zooming on all Actors: Automatic Focus+Context Split Screen Video Generation
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Kumar, Moneish; Gandhi, Vineet; Ronfard, Rémi; Gleicher, Michael; Loic Barthe and Bedrich Benes
Recordings of stage performances are easy to capture with a high-resolution camera, but are difficult to watch because the actors' faces are too small. We present an approach to automatically create a split screen video that transforms these recordings to show both the context of the scene as well as close-up details of the actors. Given a static recording of a stage performance and tracking information about the actors positions, our system generates videos showing a focus+context view based on computed close-up camera motions using crop-and zoom. The key to our approach is to compute these camera motions such that they are cinematically valid close-ups and to ensure that the set of views of the different actors are properly coordinated and presented. We pose the computation of camera motions as convex optimization that creates detailed views and smooth movements, subject to cinematic constraints such as not cutting faces with the edge of the frame. Additional constraints link the close up views of each actor, causing them to merge seamlessly when actors are close. Generated views are placed in a resulting layout that preserves the spatial relationships between actors. We demonstrate our results on a variety of staged theater and dance performances.
Performance-Based Biped Control using a Consumer Depth Camera
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Lee, Yoonsang; Kwon, Taesoo; Loic Barthe and Bedrich Benes
We present a technique for controlling physically simulated characters using user inputs from an off-the-shelf depth camera. Our controller takes a real-time stream of user poses as input, and simulates a stream of target poses of a biped based on it. The simulated biped mimics the user's actions while moving forward at a modest speed and maintaining balance. The controller is parameterized over a set of modulated reference motions that aims to cover the range of possible user actions. For real-time simulation, the best set of control parameters for the current input pose is chosen from the parameterized sets of pre-computed control parameters via a regression method. By applying the chosen parameters at each moment, the simulated biped can imitate a range of user actions while walking in various interactive scenarios.
Computational Light Painting Using a Virtual Exposure
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Salamon, Nestor Z.; Lancelle, Marcel; Eisemann, Elmar; Loic Barthe and Bedrich Benes
Light painting is an artform where a light source is moved during a long-exposure shot, creating trails resembling a stroke on a canvas. It is very difficult to perform because the light source needs to be moved at the intended speed and along a precise trajectory. Additionally, images can be corrupted by the person moving the light. We propose computational light painting, which avoids such artifacts and is easy to use. Taking a video of the moving light as input, a virtual exposure allows us to draw the intended light positions in a post-process. We support animation, as well as 3D light sculpting, with high-quality results.
Analysis and Controlled Synthesis of Inhomogeneous Textures
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Zhou, Yang; Shi, Huajie; Lischinski, Dani; Gong, Minglun; Kopf, Johannes; Huang, Hui; Loic Barthe and Bedrich Benes
Many interesting real-world textures are inhomogeneous and/or anisotropic. An inhomogeneous texture is one where various visual properties exhibit significant changes across the texture's spatial domain. Examples include perceptible changes in surface color, lighting, local texture pattern and/or its apparent scale, and weathering effects, which may vary abruptly, or in a continuous fashion. An anisotropic texture is one where the local patterns exhibit a preferred orientation, which also may vary across the spatial domain. While many example-based texture synthesis methods can be highly effective when synthesizing uniform (stationary) isotropic textures, synthesizing highly non-uniform textures, or ones with spatially varying orientation, is a considerably more challenging task, which so far has remained underexplored. In this paper, we propose a new method for automatic analysis and controlled synthesis of such textures. Given an input texture exemplar, our method generates a source guidance map comprising: (i) a scalar progression channel that attempts to capture the low frequency spatial changes in color, lighting, and local pattern combined, and (ii) a direction field that captures the local dominant orientation of the texture. Having augmented the texture exemplar with this guidance map, users can exercise better control over the synthesized result by providing easily specified target guidance maps, which are used to constrain the synthesis process.
Fully Spectral Partial Shape Matching
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Litany, Or; Rodolà, Emanuele; Bronstein, Alex M.; Bronstein, Michael M.; Loic Barthe and Bedrich Benes
We propose an efficient procedure for calculating partial dense intrinsic correspondence between deformable shapes performed entirely in the spectral domain. Our technique relies on the recently introduced partial functional maps formalism and on the joint approximate diagonalization (JAD) of the Laplace-Beltrami operators previously introduced for matching non-isometric shapes. We show that a variant of the JAD problem with an appropriately modified coupling term (surprisingly) allows to construct quasi-harmonic bases localized on the latent corresponding parts. This circumvents the need to explicitly compute the unknown parts by means of the cumbersome alternating minimization used in the previous approaches, and allows performing all the calculations in the spectral domain with constant complexity independent of the number of shape vertices. We provide an extensive evaluation of the proposed technique on standard non-rigid correspondence benchmarks and show state-of-the-art performance in various settings, including partiality and the presence of topological noise.
STD: Student's t-Distribution of Slopes for Microfacet Based BSDFs
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Ribardière, Mickael; Bringier, Benjamin; Meneveaux, Daniel; Simonot, Lionel; Loic Barthe and Bedrich Benes
This paper focuses on microfacet reflectance models, and more precisely on the definition of a new and more general distribution function, which includes both Beckmann's and GGX distributions widely used in the computer graphics community. Therefore, our model makes use of an additional parameter g, which controls the distribution function slope and tail height. It actually corresponds to a bivariate Student's t-distribution in slopes space and it is presented with the associated analytical formulation of the geometric attenuation factor derived from Smith representation.We also provide the analytical derivations for importance sampling isotropic and anisotropic materials. As shown in the results, this new representation offers a finer control of a wide range of materials, while extending the capabilities of fitting parameters with captured data.
Informative Descriptor Preservation via Commutativity for Shape Matching
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Nogneng, Dorian; Ovsjanikov, Maks; Loic Barthe and Bedrich Benes
We consider the problem of non-rigid shape matching, and specifically the functional maps framework that was recently proposed to find correspondences between shapes. A key step in this framework is to formulate descriptor preservation constraints that help to encode the information (e.g., geometric or appearance) that must be preserved by the unknown map. In this paper, we show that considering descriptors as linear operators acting on functions through multiplication, rather than as simple scalar-valued signals, allows to extract significantly more information from a given descriptor and ultimately results in a more accurate functional map estimation. Namely, we show that descriptor preservation constraints can be formulated via commutativity with respect to the unknown map, which can be conveniently encoded by considering relations between matrices in the discrete setting. As a result, when the vector space spanned by the descriptors has a dimension smaller than that of the reduced basis, our optimization may still provide a fully-constrained system leading to accurate point-to-point correspondences, while previous methods might not. We demonstrate on a wide variety of experiments that our approach leads to significant improvement for functional map estimation by helping to reduce the number of necessary descriptor constraints by an order of magnitude, even given an increase in the size of the reduced basis.
Flicker Observer Effect: Guiding Attention Through High Frequency Flicker in Images
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Waldin, Nicholas; Waldner, Manuela; Viola, Ivan; Loic Barthe and Bedrich Benes
Drawing the user's gaze to an important item in an image or a graphical user interface is a common challenge. Usually, some form of highlighting is used, such as a clearly distinct color or a border around the item. Flicker can also be very salient, but is often perceived as annoying. In this paper, we explore high frequency flicker (60 to 72 Hz) to guide the user's attention in an image. At such high frequencies, the critical flicker frequency (CFF) threshold is reached, which makes the flicker appear to fuse into a stable signal. However, the CFF is not uniform across the visual field, but is higher in the peripheral vision at normal lighting conditions. Through experiments, we show that high frequency flicker can be easily detected by observers in the peripheral vision, but the signal is hardly visible in the foveal vision when users directly look at the flickering patch. We demonstrate that this property can be used to draw the user's attention to important image regions using a standard high refresh-rate computer monitor with minimal visible modifications to the image. In an uncalibrated visual search task, users could in a crowded image easily spot the specified search targets flickering with very high frequency. They also reported that high frequency flicker was distracting when they had to attend to another region, while it was hardly noticeable when looking at the flickering region itself.
Design Transformations for Rule-based Procedural Modeling
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Lienhard, Stefan; Lau, Cheryl; Müller, Pascal; Wonka, Peter; Pauly, Mark; Loic Barthe and Bedrich Benes
We introduce design transformations for rule-based procedural models, e.g., for buildings and plants. Given two or more procedural designs, each specified by a grammar, a design transformation combines elements of the existing designs to generate new designs. We introduce two technical components to enable design transformations. First, we extend the concept of discrete rule switching to rule merging, leading to a very large shape space for combining procedural models. Second, we propose an algorithm to jointly derive two or more grammars, called grammar co-derivation. We demonstrate two applications of our work: we show that our framework leads to a larger variety of models than previous work, and we show fine-grained transformation sequences between two procedural models.
Hybrid Mesh-volume LoDs for All-scale Pre-filtering of Complex 3D Assets
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Loubet, Guillaume; Neyret, Fabrice; Loic Barthe and Bedrich Benes
We address the problem of constructing appearance-preserving level of details (LoDs) of complex 3D models such as trees. We propose a hybrid method that combines the strengths of mesh and volume representations. Our main idea is to separate macroscopic (i.e. larger than the target spatial resolution) and microscopic (sub-resolution) surfaces at each scale and to treat them differently, because meshes are very efficient at representing macroscopic surfaces while sub-resolution geometry benefits from volumetric approximations. We introduce a new algorithm that detects the macroscopic surfaces of a mesh for a given resolution. We simplify these surfaces with edge collapses and we provide a method for pre-filtering their normal distributions and albedos. To approximate microscopic details, we use a heterogeneous microflake participating medium and we introduce a new artifact-free voxelization algorithm that preserves local occlusion. Thanks to our macroscopic surface analysis, our algorithm is fully automatic and it generates seamless LoDs at arbitrarily coarse resolutions for a wide range of 3D models.
Diffusion Diagrams: Voronoi Cells and Centroids from Diffusion
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Herholz, Philipp; Haase, Felix; Alexa, Marc; Loic Barthe and Bedrich Benes
We define Voronoi cells and centroids based on heat diffusion. These heat cells and heat centroids coincide with the common definitions in Euclidean spaces. On curved surfaces they compare favorably with definitions based on geodesics: they are smooth and can be computed in a stable way with a single linear solve. We analyze the numerics of this approach and can show that diffusion diagrams converge quadratically against the smooth case under mesh refinement, which is better than other common discretization of distance measures in curved spaces. By factorizing the system matrix in a preprocess, computing Voronoi diagrams or centroids amounts to just back-substitution. We show how to localize this operation so that the complexity is linear in the size of the cells and not the underlying mesh. We provide several example applications that show how to benefit from this approach.
Parallel BVH Construction using Progressive Hierarchical Refinement
(The Eurographics Association and John Wiley & Sons Ltd., 2017) Hendrich, Jakub; Meister, Daniel; Bittner, Jiří; Loic Barthe and Bedrich Benes
We propose a novel algorithm for construction of bounding volume hierarchies (BVHs) for multi-core CPU architectures. The algorithm constructs the BVH by a divisive top-down approach using a progressively refined cut of an existing auxiliary BVH. We propose a new strategy for refining the cut that significantly reduces the workload of individual steps of BVH construction. Additionally, we propose a new method for integrating spatial splits into the BVH construction algorithm. The auxiliary BVH is constructed using a very fast method such as LBVH based on Morton codes. We show that the method provides a very good trade-off between the build time and ray tracing performance. We evaluated the method within the Embree ray tracing framework and show that it compares favorably with the Embree BVH builders regarding build time while maintaining comparable ray tracing speed.

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