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We present a novel and effective method for modeling a developable surface to simulate paper bending in interactive and animation applications. The method exploits the representation of a developable surface as the envelope of rectifying planes of a curve in 3D, which is therefore necessarily a geodesic on the surface. We manipulate the geodesic to provide intuitive shape control for modeling paper bending. Our method ensures a natural continuous isometric deformation from a piece of bent paper to its flat state without any stretching. Test examples show that the new scheme is fast, accurate, and easy to use, thus providing an effective approach to interactive paper bending. We also show how to handle non-convex piecewise smooth developable surfaces. [ABSTRACT FROM AUTHOR]

We present a physically inspired model of wax crayons, which synthesizes drawings from collections of user-specified strokes. Paper is represented by a height-field texture, and a crayon is modeled with a 2D mask that evolves as it interacts with the paper. The amount of wax deposition is computed based on the crayon contact profile, contact force and friction. Previously deposited wax is smeared by crayon action, based on wax softness and contact information. Deposited wax can also be carved from the paper by the crayon and redeposited at another location. The distributed wax is rendered using a simplified Kubelka–Monk model, which approximates light transmission and scattering effects. [ABSTRACT FROM AUTHOR]

The article presents information on selected papers from the 18th Brazilian Symposium on Computer Graphics and Image Processing Rio Grande do Norte, Brazil. The paper "A Randomized Approach for Patch-based Texture Synthesis Using Wavelets" by Leandro Tonietto, Marcelo Walter and Claudio R. Jung, discusses a wavelet-based approach for selecting blocks in patch-based texture synthesis. The second paper was "GEncode: Geometry-driven Compression for General Meshes" by Thomas Lewiner and colleagues.

Papercraft models can serve as inexpensive prototypes in shape design applications. However, in making the models some geometric detail is necessarily lost, and artificial creases may be visible, thereby limiting the utility of these models. To compensate for these practical limitations, we introduce the use of printed patterns on papercraft models to enhance the perception of the shape they are intended to represent. We propose pattern generation schemes that modulate the sizes, directions, and densities of glyphs of patterns based on geometric attributes. We present a psychophysical experiment designed to explore the effect that printed patterns have on the perception of the papercraft model shapes. We find that models with printed patterns are perceived to represent the intended shape more accurately, and, further, that the type of printed pattern has an impact on the perceived shape. [ABSTRACT FROM AUTHOR]

We propose a generic pigment model suitable for digital painting in a wide range of genres including traditional Chinese painting and water-based painting. The model embodies a simulation of the pigment-water solution and its interaction with the brush and the paper at the level of pigment particles; such a level of detail is needed for achieving highly intricate effects by the artist. The simulation covers pigment diffusion and sorption processes at the paper surface, and aspects of pigment particle deposition on the paper. We follow rules and formulations from quantitative studies of adsorption and diffusion processes in surface chemistry and the textile industry. The result is a pigment model that spans a continuum from the very wet to the very dry brush stroke effects. We also propose a new pigment mixing method based on machine learning techniques to emulate pigment mixing in real life as well as to support the creation of new artificial pigments. To experiment with the proposed model, we embedded the model in a sophisticated digital brush system. The combined system exhibits interactive speed on a modest PC platform. provides supplementary materials for this paper. [ABSTRACT FROM AUTHOR]

It remains a challenge to robustly and rapidly extract high quality curve skeletons from 3D models of closed surfaces, especially when there are nearby surface sheets. In this paper, we address this challenge by improving the use of LOP (Locally Optimal Projection) to adaptively contract medial surfaces of 3D models. LOP was originally designed to optimize a raw scanned point cloud to its corresponding geometry surface. It has the effect of contraction, and the contraction amplitude is controlled by a support radius. Our improvements are twofold. First, we constrain the LOP operator applied in the 2D medial surface instead of in the 3D space and take a local region growing strategy to find neighborhoods for implementing LOP. Thus, we avoid interference between disconnected surface parts and accelerate the process due to the reduced search space. Second, we adaptively adjust the support radii to have different parts of the medial surface contracted adaptively and synchronously for generating connected skeletal curves. In this paper, we demonstrate that our method allows for each part of the medial surface to be contracted symmetrically to its center line and is insensitive to surface noises. Thus, with our method, centered and connected high quality curve skeletons can be extracted robustly and rapidly, even for models with nearby surface sheets. Experimental results highlight the effectiveness and high efficiency of the method, even for noisy and topologically complex models, making it superior to other state‐of‐the‐art methods. [ABSTRACT FROM AUTHOR]

Abstract: Watercolor paintings have a unique look that mixes subtle color gradients and sophisticated diffusion patterns. This makes them immediately recognizable and gives them a unique appeal. Creating such paintings requires advanced skills that are beyond the reach of most people. Even for trained artists, producing several copies of a painting is a tedious task. One can resort to scanning an existing painting and printing replicas, but these are all identical and have lost an essential characteristic of a painting, its uniqueness. We address these two issues with a technique to fabricate woodblocks that we later use to create watercolor prints. The woodblocks can be reused to produce multiple copies but each print is unique due to the physical process that we introduce. We also design an image processing pipeline that helps users to create the woodblocks and describe a protocol that produces prints by carefully controlling the interplay between the paper, ink pigments, and water so that the final piece depicts the desired scene while exhibiting the distinctive features of watercolor. Our technique enables anyone with the resources to produce watercolor prints. [ABSTRACT FROM AUTHOR]

The article reports on the education program at Eurographics 2006. The program was developed to show exemplary work of educators who teach courses in computer graphics or use computer graphics to teach another topic. The session on the use of computer graphics in education included methods for using computer graphics for teaching topics. The session on teaching advanced concepts in computer graphics is centered on computer graphics education in more advanced computer science courses.

This paper shows how the Virtual Reality (VR) course can naturally extend and practice a wide range of Computer Graphics (CG) principles and programming techniques. Thanks to real-time processing requirements, attention is paid to efficient modeling conventions, time-saving rendering approaches, and user interfaces allowing a smooth navigation in a virtual environment. All these issues play an important role especially when designing virtual worlds targeted to the web, i.e. utilizing VRML/X3D standards. The paper presents a structure and related information of the VR course that has been taught at various universities during the last 6 years. Our experience clearly demonstrates that students appreciate its contents even if they already completed courses on 3D graphics. [ABSTRACT FROM AUTHOR]

In this paper we propose a method to synthesize a virtual copperplate print image based on physical model as a non-photorealistic rendering in Computer Graphics. In particular we pick out the drypoint from many existing copperplate printing techniques. A drypoint print has a remarkable feature that ridged burrs are arising out of the copperplate and the printed lines are slightly ragged and fuzzy. Our method consists of four sub-processes: plate making, ink applying, wiping and printing. Each process simulates the physical actions and phenomena observed in the actual copperplate printing. In this study we use a small-scale print and an actual print created by a real copperplate artist for some experiments to indicate effects and availability of proposed method to synthesize a print image with the feature of drypoint. Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism [ABSTRACT FROM AUTHOR]

In a photo, motion blur can be used as an artistic style to convey motion and to direct attention. In panning or tracking shots, a moving object of interest is followed by the camera during a relatively long exposure. The goal is to get a blurred background while keeping the object sharp. Unfortunately, it can be difficult to impossible to precisely follow the object. Often, many attempts or specialized physical setups are needed. This paper presents a novel approach to create such images. For capturing, the user is only required to take a casually recorded hand‐held video that roughly follows the object. Our algorithm then produces a single image which simulates a stabilized long time exposure. This is achieved by first warping all frames such that the object of interest is aligned to a reference frame. Then, optical flow based frame interpolation is used to reduce ghosting artifacts from temporal undersampling. Finally, the frames are averaged to create the result. As our method avoids segmentation and requires little to no user interaction, even challenging sequences can be processed successfully. In addition, artistic control is available in a number of ways. The effect can also be applied to create videos with an exaggerated motion blur. Results are compared with previous methods and ground truth simulations. The effectiveness of our method is demonstrated by applying it to hundreds of datasets. The most interesting results are shown in the paper and in the supplemental material. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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 γ, 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. [ABSTRACT FROM AUTHOR]

This paper presents an efficient technique for synthesizing motions by stitching, or splicing, an upper-body motion retrieved from a motion space on top of an existing lower-body locomotion of another motion. Compared to the standard motion splicing problem, motion space splicing imposes new challenges as both the upper and lower body motions might not be known in advance. Our technique is the first motion (space) splicing technique that propagates temporal and spatial properties of the lower-body locomotion to the newly generated upper-body motion and vice versa. Whereas existing techniques only adapt the upper-body motion to fit the lower-body motion, our technique also adapts the lower-body locomotion based on the upper body task for a more coherent full-body motion. In this paper, we will show that our decoupled approach is able to generate high-fidelity full-body motion for interactive applications such as games. [ABSTRACT FROM AUTHOR]

Diffusion curves are a powerful vector graphic representation that stores an image as a set of 2D Bezier curves with colors defined on either side. These colors are diffused over the image plane, resulting in smooth color regions as well as sharp boundaries. In this paper, we introduce a new automatic diffusion curve coloring algorithm. We start by defining a geometric heuristic for the maximum density of color control points along the image curves. Following this, we present a new algorithm to set the colors of these points so that the resulting diffused image is as close as possible to a source image in a least squares sense. We compare our coloring solution to the existing one which fails for textured regions, small features, and inaccurately placed curves. The second contribution of the paper is to extend the diffusion curve representation to include texture details based on Gabor noise. Like the curves themselves, the defined texture is resolution independent, and represented compactly. We define methods to automatically make an initial guess for the noise texure, and we provide intuitive manual controls to edit the parameters of the Gabor noise. Finally, we show that the diffusion curve representation itself extends to storing any number of attributes in an image, and we demonstrate this functionality with image stippling an hatching applications. [ABSTRACT FROM AUTHOR]

In this paper, a novel concept, Affective Modelling, is introduced to encapsulate the idea of creating 3D models based on the emotional responses that they may invoke. Research on perceptually-related issues in Computer Graphics focuses mostly on the rendering aspect. Low-level perceptual criteria taken from established Psychology theories or identified by purposefully-designed experiments are utilised to reduce rendering effort or derive quality evaluation schemes. For modelling, similar ideas have been applied to optimise the level of geometrical details. High-level cognitive responses such as emotions/feelings are less addressed in graphics literatures. This paper investigates the possibility of incorporating emotional/affective factors for 3D model creations. Using a glasses frame model as our test case, we demonstrate a methodological framework to build the links between human emotional responses and geometrical features. We design and carry out a factorial experiment to systematically analyse how certain shape factors individually and interactively influence the viewer's impression of the shape of glasses frames. The findings serve as a basis for establishing computational models that facilitate emotionally-guided 3D modelling. [ABSTRACT FROM AUTHOR]

This paper proposes a real-time simulation technique for thin shells undergoing large deformation. Shells are thin objects such as leaves and papers that can be abstracted as 2D structures. Development of a satisfactory physical model that runs in real-time but produces visually convincing animation of thin shells has been remaining a challenge in computer graphics. Rather than resorting to shell theory which involves the most complex formulations in continuum mechanics, we adopt the energy functions from the discrete shells proposed by Grinspun et al. [ GHDS03 ]. For real-time integration of the governing equation, we develop a modal warping technique for shells. This new simulation framework results from making extensions to the original modal warping technique [ CK05 ] which was developed for the simulation of 3D solids. We report experimental results, which show that the proposed method runs in real-time even for large meshes, and that it can simulate large bending and/or twisting deformations with acceptable realism. [ABSTRACT FROM AUTHOR]

This paper presents a universal method for constructing interpolatory subdivision schemes from known approximatory subdivisions. The method establishes geometric rules of the associated interpolatory subdivision through addition of further weighted averaging operations to the approximatory subdivision. The paper thus provides a novel approach for designing new interpolatory subdivision schemes. In addition, a family of subdivision surfaces varying from the given approximatory scheme to its associated interpolatory scheme, namely the blending subdivisions, can also be established. Based on the proposed method, variants of several known interpolatory subdivision schemes are constructed. A new interpolatory subdivision scheme is also developed using the same technique. Brief analysis of a family of blending subdivisions associated with the Loop subdivision scheme demonstrates that this particular family of subdivisions are globally C1 continuous while maintaining bounded curvature for regular meshes. As a further extension of the blending subdivisions, a volume-preserving subdivision strategy is also proposed in the paper. [ABSTRACT FROM AUTHOR]

Real-time rendering of photo-realistic humans is considerably outside the scope of current consumer-level computer hardware. There are many techniques, which attempt to bridge the gap between what is desired and what is possible. This paper aims to give an overview of the techniques designed to alter the complexity of the model's geometry (level of detail), or replace it with a flat image (visual impostor) and to improve the lighting model (lighting and shadows). Recent years have shown a boom in the power and availability of consumer-level programmable graphics processors, thus techniques that make use of these features are coming to the forefront. [ABSTRACT FROM AUTHOR]

Voxel traversing along a line in a uniformly divided voxel space is frequently needed in different applications of computer graphics. The paper presents a new integer one-pass algorithm for this problem. In 2D, the proposed approach is based on a modification of the well-known Bresenham algorithm. The algorithm is then extended in 3D where a special case may occur. It is characterized by a simple discriminator. A derivation for this discriminator given in the paper confirms that all calculations can be realized using only integer arithmetic. In this way, the accumulation of rounding errors is completely eliminated, and a robust and compact implementation can be easily achieved. One of the main advantages of the proposed algorithm is that it visits 1–3 voxels during each iteration thus assuring its efficiency. The algorithm has been compared with other algorithms for voxel traversing by measuring spent CPU time. For comparison, Cleary & Wyvill's, Amanatides & Woo's, and Code-based algorithm have been used. The proposed algorithm is faster than the referenced algorithms. [ABSTRACT FROM AUTHOR]

This paper presents an efficient approach for generating weathering effects with detailed appearance variations in a single image. Previous approaches merely change chroma or reflectance of weathered objects, which is not sufficient for materials with detailed shading and texture variations, such as growing moss and peeling plaster. Our method propagates such detailed features via seamless patch-based synthesis driven by weathering degree distribution. Unlike previous methods, the weathering degrees are calculated efficiently using Radial Basis Functions even for materials with wide color variations. We use graph cut-based optimization to identify the most weathered region as a 'weathering exemplar', from which we sample weathering patches. We demonstrate our method enables us to generate various types of detailed weathering effects interactively. [ABSTRACT FROM AUTHOR]

This paper poses the problem of fabricating physical construction sets from example geometry: A construction set provides a small number of different types of building blocks from which the example model as well as many similar variants can be reassembled. This process is formalized by tiling grammars. Our core contribution is an approach for simplifying tiling grammars such that we obtain physically manufacturable building blocks of controllable granularity while retaining variability, i.e., the ability to construct many different, related shapes. Simplification is performed by sequences of two types of elementary Operations: non-local joint edge collapses in the tile graphs reduce the granularity of the decomposition and approximate replacement Operations reduce redundancy. We evaluate our method on abstract graph grammars in addition to computing several physical construction sets, which are manufactured using a commodity 3D printer. [ABSTRACT FROM AUTHOR]

Spectral methods have recently gained popularity in many domains of computer graphics and geometry processing, especially shape processing, computation of shape descriptors, distances, and correspondence. Spectral geometric structures are intrinsic and thus invariant to isometric deformations, are efficiently computed, and can be constructed on shapes in different representations. A notable drawback of these constructions, however, is that they are isotropic, i.e., insensitive to direction. In this paper, we show how to construct direction-sensitive spectral feature descriptors using anisotropic diffusion on meshes and point clouds. The core of our construction are directed local kernels acting similarly to steerable filters, which are learned in a task-specific manner. Remarkably, while being intrinsic, our descriptors allow to disambiguate reflection symmetries. We show the application of anisotropic descriptors for problems of shape correspondence on meshes and point clouds, achieving results significantly better than state-of-the-art methods. [ABSTRACT FROM AUTHOR]

This paper generalizes the well-known Diffusion Curves Images (DCI), which are composed of a set of Bezier curves with colors specified on either side. These colors are diffused as Laplace functions over the image domain, which results in smooth color gradients interrupted by the Bezier curves. Our new formulation allows for more color control away from the boundary, providing a similar expressive power as recent Bilaplace image models without introducing associated issues and computational costs. The new model is based on a special Laplace function blending and a new edge blur formulation. We demonstrate that given some user-defined boundary curves over an input raster image, fitting colors and edge blur from the image to the new model and subsequent editing and animation is equally convenient as with DCIs. Numerous examples and comparisons to DCIs are presented. [ABSTRACT FROM AUTHOR]

Current HDR acquisition techniques are based on either (i) fusing multibracketed, low dynamic range (LDR) images, (ii) modifying existing hardware and capturing different exposures simultaneously with multiple sensors, or (iii) reconstructing a single image with spatially-varying pixel exposures. In this paper, we propose a novel algorithm to recover high-quality HDRI images from a single, coded exposure. The proposed reconstruction method builds on recently-introduced ideas of convolutional sparse coding (CSC); this paper demonstrates how to make CSC practical for HDR imaging. We demonstrate that the proposed algorithm achieves higher-quality reconstructions than alternative methods, we evaluate optical coding schemes, analyze algorithmic parameters, and build a prototype coded HDR camera that demonstrates the utility of convolutional sparse HDRI coding with a custom hardware platform. [ABSTRACT FROM AUTHOR]

In this paper, we study a method to synthesize a multicolor virtual woodblock print by using several virtual woodblocks. It consists of two sections: carving and printing, to synthesize a virtual print. In the carving section, virtual woodblocks are generated by a user with supporting of an automatically carving method based on feature extraction of a gray value image. And woodblocks are also generated automatically by using a full-color image as a draft. In the printing section, a “paper sheet", a “printing brush" and “ink" are prepared in addition to the “woodblock" in the virtual space and the user synthesizes a woodblock print interactively. As the printing factors, a color of ink, a moisture value and a grain change the finish of the print. Using several virtual woodblocks and printing to a paper sheet in succession, a printing image of each woodblock is combined based on the printing factors and a multicolor virtual prints is synthesized. [ABSTRACT FROM AUTHOR]

Sparse localized decomposition is a useful technique to extract meaningful deformation components out of a training set of mesh data. However, existing methods cannot capture large rotational motion in the given mesh dataset. In this paper we present a new decomposition technique based on deformation gradients. Given a mesh dataset, the deformation gradient field is extracted, and decomposed into two groups: rotation field and stretching field, through polar decomposition. These two groups of deformation information are further processed through the sparse localized decomposition into the desired components. These sparse localized components can be linearly combined to form a meaningful deformation gradient field, and can be used to reconstruct the mesh through a least squares optimization step. Our experiments show that the proposed method addresses the rotation problem associated with traditional deformation decomposition techniques, making it suitable to handle not only stretched deformations, but also articulated motions that involve large rotations. [ABSTRACT FROM AUTHOR]

This paper proposes a novel hybrid particle-grid approach to liquid simulation, which uses the fluid-implicit-particle (FLIP) method to resolve the liquid motion and a grid-based particle correction method to complement FLIP. The correction process addresses the high-frequency errors in FLIP ensuring that the particles are properly distributed. The proposed approach enables the corrective procedure to avoid directly processing the particle relationships and supports flexible corrective forces. The proposed technique effectively and efficiently improves the distribution of the particles and therefore enhances the overall simulation quality. The experimental results confirm that the technique is able to conserve the liquid volume and to produce dynamic surface motions, thin liquid sheets, and smooth surfaces without disturbing artifacts such as bumpy noise. [ABSTRACT FROM AUTHOR]

Visual cryptography is an encryption technique that hides a secret image by distributing it between some shared images made up of seemingly random black-and-white pixels. Extended visual cryptography (EVC) goes further in that the shared images instead represent meaningful binary pictures. The original approach to EVC suffered from low contrast, so later papers considered how to improve the visual quality of the results by enhancing contrast of the shared images. This work further improves the appearance of the shared images by preserving edge structures within them using a framework of dithering followed by a detail recovery operation. We are also careful to suppress noise in smooth areas. [ABSTRACT FROM AUTHOR]

The basic idea of curve network-based design is to construct smoothly connected surface patches, that interpolate boundaries and cross-derivatives extracted from the curve network. While the majority of applications demands only tangent plane (G1) continuity between the adjacent patches, curvature continuous connections (G2) may also be required. Examples include special curve network configurations with supplemented internal edges, 'master-slave' curvature constraints, and general topology surface approximations over meshes. The first step is to assign optimal surface curvatures to the nodes of the curve network; we discuss different optimization procedures for various types of nodes. Then interpolant surfaces called parabolic ribbons are created along the patch boundaries, which carry first and second derivative constraints. Our construction guarantees that the neighboring ribbons, and thus the respective transfinite patches, will be G2 continuous. We extend Gregory's multi-sided surface scheme in order to handle parabolic ribbons, involving the blending functions, and a new sweepline parameterization. A few simple examples conclude the paper. [ABSTRACT FROM AUTHOR]

This paper proposes a new approach for color transfer between two images. Our method is unique in its consideration of the scene illumination and the constraint that the mapped image must be within the color gamut of the target image. Specifically, our approach first performs a white-balance step on both images to remove color casts caused by different illuminations in the source and target image. We then align each image to share the same 'white axis' and perform a gradient preserving histogram matching technique along this axis to match the tone distribution between the two images. We show that this illuminant-aware strategy gives a better result than directly working with the original source and target image's luminance channel as done by many previous methods. Afterwards, our method performs a full gamut-based mapping technique rather than processing each channel separately. This guarantees that the colors of our transferred image lie within the target gamut. Our experimental results show that this combined illuminant-aware and gamut-based strategy produces more compelling results than previous methods. We detail our approach and demonstrate its effectiveness on a number of examples. [ABSTRACT FROM AUTHOR]

A practical way to generate a high dynamic range (HDR) video using off‐the‐shelf cameras is to capture a sequence with alternating exposures and reconstruct the missing content at each frame. Unfortunately, existing approaches are typically slow and are not able to handle challenging cases. In this paper, we propose a learning‐based approach to address this difficult problem. To do this, we use two sequential convolutional neural networks (CNN) to model the entire HDR video reconstruction process. In the first step, we align the neighboring frames to the current frame by estimating the flows between them using a network, which is specifically designed for this application. We then combine the aligned and current images using another CNN to produce the final HDR frame. We perform an end‐to‐end training by minimizing the error between the reconstructed and ground truth HDR images on a set of training scenes. We produce our training data synthetically from existing HDR video datasets and simulate the imperfections of standard digital cameras using a simple approach. Experimental results demonstrate that our approach produces high‐quality HDR videos and is an order of magnitude faster than the state‐of‐the‐art techniques for sequences with two and three alternating exposures. [ABSTRACT FROM AUTHOR]

Extracting a faithful and compact representation of an animated surface mesh is an important problem for computer graphics. However, the surface‐based methods have limited approximation power for volume preservation when the animated sequences are extremely simplified. In this paper, we introduce Deformable Medial Axis Transform (DMAT), which is deformable medial mesh composed of a set of animated spheres. Starting from extracting an accurate and compact representation of a static MAT as the template and partitioning the vertices on the input surface as the correspondences for each medial primitive, we present a correspondence‐based approximation method equipped with an As‐Rigid‐As‐Possible (ARAP) deformation energy defined on medial primitives. As a result, our algorithm produces DMAT with consistent connectivity across the whole sequence, accurately approximating the input animated surfaces. [ABSTRACT FROM AUTHOR]

Accurate high‐resolution simulation of cloth is a highly desired computational tool in graphics applications. As single‐resolution simulation starts to reach the limit of computational power, we believe the future of cloth simulation is in multi‐resolution simulation. In this paper, we explore nonlinearity, adaptive smoothing, and parallelization under a full multigrid (FMG) framework. The foundation of this research is a novel nonlinear FMG method for unstructured meshes. To introduce nonlinearity into FMG, we propose to formulate the smoothing process at each resolution level as the computation of a search direction for the original high‐resolution nonlinear optimization problem. We prove that our nonlinear FMG is guaranteed to converge under various conditions and we investigate the improvements to its performance. We present an adaptive smoother which is used to reduce the computational cost in the regions with low residuals already. Compared to normal iterative solvers, our nonlinear FMG method provides faster convergence and better performance for both Newton's method and Projective Dynamics. Our experiment shows our method is efficient, accurate, stable against large time steps, and friendly with GPU parallelization. The performance of the method has a good scalability to the mesh resolution, and the method has good potential to be combined with multi‐resolution collision handling for real‐time simulation in the future. [ABSTRACT FROM AUTHOR]

This paper presents a non‐local low‐rank normal filtering method for mesh denoising. By exploring the geometric similarity between local surface patches on 3D meshes in the form of normal fields, we devise a low‐rank recovery model that filters normal vectors by means of patch groups. In summary, our method has the following key contributions. First, we present the guided normal patch covariance descriptor to analyze the similarity between patches. Second, we pack normal vectors on similar patches into the normal‐field patch‐group (NPG) matrix for rank analysis. Third, we formulate mesh denoising as a low‐rank matrix recovery problem based on the prior that the rank of the NPG matrix is high for raw meshes with noise, but can be significantly reduced for denoised meshes, whose normal vectors across similar patches should be more strongly correlated. Furthermore, we devise an objective function based on an improved truncated γ norm, and derive an optimization procedure using the alternative direction method of multipliers and iteratively re‐weighted least squares techniques. We conducted several experiments to evaluate our method using various 3D models, and compared our results against several state‐of‐the‐art methods. Experimental results show that our method consistently outperforms other methods and better preserves the fine details. [ABSTRACT FROM AUTHOR]

The article discusses various reports published within the issue. The last issue of the 25th volume of "Computer Graphics Forum" appropriately reflects the themes that summarize what Eurographics is about. The themes are innovative research, best practice and the global community. The paper by Atty, Xu and Sun reports new results in rendering soft shadow maps. The work of Fattal and Lischinski in the field of animation explores the use of pose control in physically-based motion.

This paper presents a novel content-based method for transferring the colour patterns between images. Unlike previous methods that rely on image colour statistics, our method puts an emphasis on high-level scene content analysis. We first automatically extract the foreground subject areas and background scene layout from the scene. The semantic correspondences of the regions between source and target images are established. In the second step, the source image is re-coloured in a novel optimization framework, which incorporates the extracted content information and the spatial distributions of the target colour styles. A new progressive transfer scheme is proposed to integrate the advantages of both global and local transfer algorithms, as well as avoid the over-segmentation artefact in the result. Experiments show that with a better understanding of the scene contents, our method well preserves the spatial layout, the colour distribution and the visual coherence in the transfer process. As an interesting extension, our method can also be used to re-colour video clips with spatially-varied colour effects. [ABSTRACT FROM AUTHOR]

When navigating in crowds, humans are able to move efficiently between people. They look ahead to know which path would reduce the complexity of their interactions with others. Current navigation systems for virtual agents consider long-term planning to find a path in the static environment and short-term reactions to avoid collisions with close obstacles. Recently some mid-term considerations have been added to avoid high density areas. However, there is no mid-term planning among static and dynamic obstacles that would enable the agent to look ahead and avoid difficult paths or find easy ones as humans do. In this paper, we present a system for such mid-term planning. This system is added to the navigation process between pathfinding and local avoidance to improve the navigation of virtual agents. We show the capacities of such a system using several case studies. Finally we use an energy criterion to compare trajectories computed with and without the mid-term planning. [ABSTRACT FROM AUTHOR]

An indispensable element of any practical 3D/VR/AR application is synthetic three-dimensional (3D) content. Such content is characterized by a variety of features-geometry, structure, space, appearance, animation and behaviour-which makes the modelling of 3D content a much more complex, difficult and time-consuming task than in the case of other types of content. One of the promising research directions aiming at simplification of modelling 3D content is the use of the semantic web approach. The formalism provided by semantic web techniques enables declarative knowledge-based modelling of content based on ontologies. Such modelling can be conducted at different levels of abstraction, possibly domain-specific, with inherent separation of concerns. The use of semantic web ontologies enables content representation independent of particular presentation platforms and facilitates indexing, searching and analysing content, thus contributing to increased content re-usability. A range of approaches have been proposed to permit semantic representation and modelling of synthetic 3D content. These approaches differ in the methodologies and technologies used as well as their scope and application domains. This paper provides a review of the current state of the art in representation and modelling of 3D content based on semantic web ontologies, together with a classification, characterization and discussion of the particular approaches. [ABSTRACT FROM AUTHOR]

Split-depth images use an optical illusion, which can enhance the 3D impression of a 2D animation. In split-depth images (also often called split-depth GIFs due to the commonly used file format), static virtual occluders inform of vertical or horizontal bars are added to a video clip, which leads to occlusions that are interpreted by the observer as a depth cue. In this paper, we study different factors that contribute to the illusion and propose a solution to generate split-depth images for a given RGB + depth image sequence. The presented solution builds upon a motion summarization of the object of interest (OOI) through space and time. It allows us to formulate the bar positioning as an energy-minimization problem, which we solve efficiently. We take a variety of important features into account, such as the changes of the 3D effect due to changes in the motion topology, occlusion, the proximity of bars or the OOI, and scene saliency. We conducted a number of psycho-visual experiments to derive an appropriate energy formulation. Our method helps in finding optimal positions for the bars and, thus, improves the 3D perception of the original animation. We demonstrate the effectiveness of our approach on a variety of examples. Our study with novice users shows that our approach allows them to quickly create satisfying results even for complex animations. [ABSTRACT FROM AUTHOR]

Many image editing applications rely on the analysis of image patches. In this paper, we present a method to analyze patches by embedding them to a vector space, in which the Euclidean distance reflects patch similarity. Inspired by Word2Vec, we term our approach Patch2Vec. However, there is a significant difference between words and patches. Words have a fairly small and well defined dictionary. Image patches, on the other hand, have no such dictionary and the number of different patch types is not well defined. The problem is aggravated by the fact that each patch might contain several objects and textures. Moreover, Patch2Vec should be universal because it must be able to map never-seen-before texture to the vector space. The mapping is learned by analyzing the distribution of all natural patches. We use Convolutional Neural Networks (CNN) to learn Patch2Vec. In particular, we train a CNN on labeled images with a triplet-loss objective function. The trained network encodes a given patch to a 128D vector. Patch2Vec is evaluated visually, qualitatively, and quantitatively. We then use several variants of an interactive single-click image segmentation algorithm to demonstrate the power of our method. [ABSTRACT FROM AUTHOR]

While the 3D printing technology has become increasingly popular in recent years, it suffers from two critical limitations: expensive printing material and long printing time. An effective solution is to hollow the 3D model into a shell and print the shell by parts. Unfortunately, making shell pieces tightly assembled and easy to disassemble seem to be two contradictory conditions, and there exists no easy way to satisfy them at the same time yet. In this paper, we present a computational system to design an interlocking structure of a partitioned shell model, which uses only male and female connectors to lock shell pieces in the assembled configuration. Given a mesh segmentation input, our system automatically finds an optimal installation plan specifying both the installation order and the installation directions of the pieces, and then builds the models of the shell pieces using optimized shell thickness and connector sizes. To find the optimal installation plan, we develop simulation-based and data-driven metrics, and we incorporate them into an optimal plan search algorithm with fast pruning and local optimization strategies. The whole system is automatic, except for the shape design of the key piece. The interlocking structure does not introduce new gaps on the outer surface, which would become noticeable inevitably due to limited printer precision. Our experiment shows that the assembled object is strong against separation, yet still easy to disassemble. [ABSTRACT FROM AUTHOR]

This paper presents a new two-step color transfer method which includes color mapping and detail preservation. To map source colors to target colors, which are from an image or palette, the proposed similarity-preserving color mapping algorithm uses the similarities between pixel color and dominant colors as existing algorithms and emphasizes the similarities between source image pixel colors. Detail preservation is performed by an ℒ0 gradient-preserving algorithm. It relaxes the large gradients of the sparse pixels along color region boundaries and preserves the small gradients of pixels within color regions. The proposed method preserves source image color similarity and image details well. Extensive experiments demonstrate that the proposed approach has achieved a state-of-art visual performance. [ABSTRACT FROM AUTHOR]

This paper presents a novel approach to compute high quality and noise-free soft shadows using exact visibility computations. This work relies on a theoretical framework allowing to group lines according to the geometry they intersect. From this study, we derive a new algorithm encoding lazily the visibility from a polygon. Contrary to previous works on from-polygon visibility, our approach is very robust and straightforward to implement. We apply this algorithm to solve exactly and efficiently the visibility of an area light source from any point in a scene. As a consequence, results are not sensitive to noise, contrary to soft shadows methods based on area light source sampling. We demonstrate the reliability of our approach on different scenes and configurations. [ABSTRACT FROM AUTHOR]

Despite their high popularity, common high dynamic range (HDR) methods are still limited in their practical applicability: They assume that the input images are perfectly aligned, which is often violated in practise. Our paper does not only free the user from this unrealistic limitation, but even turns the missing alignment into an advantage: By exploiting the multiple exposures, we can create a super-resolution image. The alignment step is performed by a modern energy-based optic flow approach that takes into account the varying exposure conditions. Moreover, it produces dense displacement fields with subpixel precision. As a consequence, our approach can handle arbitrary complex motion patterns, caused by severe camera shake and moving objects. Additionally, it benefits from several advantages over existing strategies: (i) It is robust under outliers (noise, occlusions, saturation problems) and allows for sharp discontinuities in the displacement field. (ii) The alignment step neither requires camera calibration nor knowledge of the exposure times. (iii) It can be efficiently implemented on CPU and GPU architectures. After the alignment is performed, we use the obtained subpixel accurate displacement fields as input for an energy-based, joint super-resolution and HDR (SR-HDR) approach. It introduces robust data terms and anisotropic smoothness terms in the SR-HDR literature. Our experiments with challenging real world data demonstrate that these novelties are pivotal for the favourable performance of our approach. [ABSTRACT FROM AUTHOR]

This paper introduces the use of a visual attention model to improve the accuracy of gaze tracking systems. Visual attention models simulate the selective attention part of the human visual system. For instance, in a bottom-up approach, a saliency map is defined for the image and gives an attention weight to every pixel of the image as a function of its colour, edge or intensity. Our algorithm uses an uncertainty window, defined by the gaze tracker accuracy, and located around the gaze point given by the tracker. Then, using a visual attention model, it searches for the most salient points, or objects, located inside this uncertainty window, and determines a novel, and hopefully, better gaze point. This combination of a gaze tracker together with a visual attention model is considered as the main contribution of the paper. We demonstrate the promising results of our method by presenting two experiments conducted in two different contexts: (1) a free exploration of a visually rich 3D virtual environment without a specific task, and (2) a video game based on gaze tracking involving a selection task. Our approach can be used to improve real-time gaze tracking systems in many interactive 3D applications such as video games or virtual reality applications. The use of a visual attention model can be adapted to any gaze tracker and the visual attention model can also be adapted to the application in which it is used. [ABSTRACT FROM AUTHOR]

Ambient occlusion has proven to be a useful tool for producing realistic images, both in offline rendering and interactive applications. In production rendering, ambient occlusion is typically computed by casting a large number of short shadow rays from each visible point, yielding unparalleled quality but long rendering times. Interactive applications typically use screen-space approximations which are fast but suffer from systematic errors due to missing information behind the nearest depth layer. In this paper, we present two efficient methods for calculating ambient occlusion so that the results match those produced by a ray tracer. The first method is targeted for rasterization-based engines, and it leverages the GPU graphics pipeline for finding occlusion relations between scene triangles and the visible points. The second method is a drop-in replacement for ambient occlusion computation in offline renderers, allowing the querying of ambient occlusion for any point in the scene. Both methods are based on the principle of simultaneously computing the result of all shadow rays for a single receiver point. [ABSTRACT FROM AUTHOR]

Collages have been a common form of artistic expression since their first appearance in China around 200 BC. Recently, with the advance of digital cameras and digital image editing tools, collages have gained popularity also as a summarization tool. This paper proposes an approach for automating collage construction, which is based on assembling regions of interest of arbitrary shape in a puzzle-like manner. We show that this approach produces collages that are informative, compact, and eye-pleasing. This is obtained by following artistic principles and assembling the extracted cutouts such that their shapes complete each other. [ABSTRACT FROM AUTHOR]

Woven cloth can commonly be seen in daily life and also in animation. Unless prevented in some way, woven cloth usually frays at the edges. However, in computer graphics, woven cloth is typically modeled as a continuum sheet, which is not suitable for representing frays. This paper proposes a model that allows yarn movement and slippage during cloth tearing. Drawing upon techniques from textile and mechanical engineering fields, we model cloth as woven yarn crossings where each yarn can be independently torn when the strain limit is reached. To make the model practical for graphics applications, we simulate only tearing part of cloth with a yarn-level model using a simple constrained mass-spring system for computational efficiency. We designed conditions for switching from a standard continuum sheet model to our yarn-level model, so that frays can be initiated and propagated along the torn lines. Results show that our method can achieve plausible tearing cloth animation with frayed edges. [ABSTRACT FROM AUTHOR]

Color transfer is an image processing technique which can produce a new image combining one source image's contents with another image's color style. While being able to produce convincing results, however, Reinhard et al.'s pioneering work has two problems—mixing up of colors in different regions and the fidelity problem. Many local color transfer algorithms have been proposed to resolve the first problem, but the second problem was paid few attentions. In this paper, a novel color transfer algorithm is presented to resolve the fidelity problem of color transfer in terms of scene details and colors. It's well known that human visual system is more sensitive to local intensity differences than to intensity itself. We thus consider that preserving the color gradient is necessary for scene fidelity. We formulate the color transfer problem as an optimization problem and solve it in two steps—histogram matching and a gradient-preserving optimization. Following the idea of the fidelity in terms of color and gradient, we also propose a metric for objectively evaluating the performance of example-based color transfer algorithms. The experimental results show the validity and high fidelity of our algorithm and that it can be used to deal with local color transfer. [ABSTRACT FROM AUTHOR]