Short Presentations

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https://diglib.eg.org/handle/10.2312/244

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Adaptive Brush Stroke Generation for Painterly Rendering
(Eurographics Association, 2004) Park ChungAng, Youngsup; Yoon, Kyunghyun; M. Alexa and E. Galin
We propose adaptive brush stroke generation for source images, using reference data. Colors used are formed by actual palette colors from artists. To create the palette, we have referred mostly to colors used in Van Gogh’s works and determined the color of brush strokes by transferring it to the most similar one, through comparing colors used in source images and the palette colors. Also, by referring to the edge orientation of source images, we have applied a brush stroke orientation that surrounds the edges. The sizes were determined depending on the different sizes of the objects from wide to narrow brushes. Finally, we applied spline curve shapes. The brush strokes created in such method, were applied separately according to its segmented images, and composed after rendering.
A Color Decomposition Method for Preserving Ukiyo-e Woodblocks
(Eurographics Association, 2004) Terai, Tomokazu; Mizuno, Shinji; Okada, Minoru; M. Alexa and E. Galin
In this paper we propose a color decomposition method for multicolor printing of watercolors including areas overlapping each print layer. Watercolors have an important feature that the observed colors are different on the printing order. The proposed method is based on a particle density model for expressing the effects of watercolors. The approach of this method is to solve an inverse problem, that is, determining a printed area corresponding to a watercolor from an observed image. Our purpose in this study is to estimate woodblocks from a woodblock print. The authors have already proposed a non-photorealistic rendering method to produce virtual woodblock prints. This approach can be utilized to Ukiyo-e. An Ukiyo-e print is created from several woodblocks with several watercolors, and has a mixing color expression similar to the effects of watercolor painting. The color decomposition method can be applied to produce virtual woodblocks in the virtual woodblock printing. The results of woodblock estimation will be utilized to preserve the techniques and prints of Ukiyo-e.
Enriching Animation Databases
(Eurographics Association, 2004) Ahmed, Amr; Mokhtarian, Farzin; Hilton, Adrian; M. Alexa and E. Galin
The paper presents a framework for enriching an existing basic animation databse by modifying existing motions to generate a variety of new motions. Intuitively controlled motion varities are generated on demand which reduces the storage requirements, avoids recapturing missing variations, and provides greater flexibility and utilisation of existing clips. An improved root-trajectory blending is introduced that overcomes the limitations of ordinary blending (including flipping of the root trajectory when blending motions of opposite path-curvature or opposite directions). A novel synchronised mirror technique is also introduced.
Frontier Sets: A Partitioning Scheme to Enable Scalable Virtual Environments
(Eurographics Association, 2004) Steed, Anthony; Angus, Cameron; M. Alexa and E. Galin
We present a new spatial partitioning scheme called frontier sets. Frontier sets build on the notion of a potentially visible set (PVS) [ARB90, TS91]. In a PVS a world is sub-divided into cells and for each cell all the other cells that can be seen are computed. Frontier sets represent regions of mutual invisibility. One frontier in a frontier set considers pairs of cells, A and B. It lists two sets of cells, FAB and FBA. From no cell in FAB is any cell in FBA visible and vice-versa. We have used frontier sets to investigate peer-to-peer networking schemes for networked virtual environments. Preliminary investigation of simulations within the Quake II game engine shows that frontiers have significant promise and may allow a new class of scalable peer-to-peer game infrastructures to emerge.
A Generic Method for Geometric Contraints Detection
(Eurographics Association, 2004) Salvati, Marc; Lecallennec, Benoît; Boulic, Ronan; M. Alexa and E. Galin
In this paper, we present a generic method to automatically detect geometric constraints on motion capture animations. At each frame, elementary geometric constraints are computed with respect to a reference which can either be the world coordinate system or any moving object in the scene. We then use constraint-related concepts of union and intersection to merge the elementary constraints together and/or to generate new ones. Finally, our algorithm provides an exhaustive list of geometric constraints with an accurate evaluation of their duration. The detected constraints can characterize virtual human motion (e.g. footprints) as well as interactions with moving objects of the scene (e.g. a hand touching a ball). While our approach also detects sliding geometric constraints, we focus our discussion on detecting positional geometric constraints.
Interactive Modeling of Mushrooms
(Eurographics Association, 2004) Desbenoit, Brett; Vanderhaghe, David; Galin, Eric; Grosjean, Jerôme; M. Alexa and E. Galin
This paper presents a fast and efficient method for modeling mushrooms. Starting from a real world image, the designer defines a silhouette and specifies deformation parameters. Our system then automatically generates a textured triangle mesh model using a procedural modeling pipeline. This approach enables us to create a vast variety of shapes easily using shape morphing.
Interactive Physically-based Animation System for Dense Meshes
(Eurographics Association, 2004) Kondo, Ryo; Kanai, Takashi; M. Alexa and E. Galin
In this paper we describe an interactive physically-based animation system for dense meshes. Our method extracts a coarse mesh from an original mesh to make a tetrahedral mesh for the reduction of computational costs. For computing reaction forces we precompute penetration depth values and gradients at mesh vertices by creating a distance field. They are interpolated when collisions are detected and are used for the calculation of forces with a penalty method. Our method can handle dense meshes with physically-based animation and collision response at interactive frame rates.
Modeling clouds shape
(Eurographics Association, 2004) Bouthors, Antoine; Neyret, Fabrice; M. Alexa and E. Galin
We propose a model for representing the shape of cumulus clouds.We draw on several approaches that we combine and extend: We store a hierarchy of quasi-spherical particles (or blobs) living on top of each other. The shape of these particles is defined by an implicit field which deforms under the influence of neighbor particles. We define a set of shaders to simulate a volumetric appearance in the spirit of Gardner's textured ellipsoids, to make the shape appear continuous, and to account for dedicated shading effects. In this paper we deal only with the definition of the shape. However, we believe that this model is well suited to be integrated with particle animation and advanced rendering.
Modulating View-dependent Textures
(Eurographics Association, 2004) Jagersand, Martin; Cobzas, Dana; Yerex, Keith; M. Alexa and E. Galin
We present a texturing approach for image-based modeling and rendering, where instead of using one (or a blend of a few) sample images, new view dependent textures are synthesized by modulating a differential texture basis. The texture basis models the first order intensity variation due to image projection errors and parallax for a nonlinear projective camera. Experimentally we compare rendered views to ground truth real images and quantify how the texture basis can generate a more accurate rendering compared to conventional view dependent textures.
An Oriented Particle and Generalized Spring Model for Fast Prototyping Deformable Objects
(Eurographics Association, 2004) Jeong, Il-Kwon; Lee, Inho; M. Alexa and E. Galin
We present a new mass-spring system, in particular, by using an oriented particle and generalized spring model, which can be used for fast prototyping or animation of deformable objects. Conventional mass-spring system is widely used especially in cloth animation. However animating deformable objects such as a jelly cube requires extra diagonal springs in addition to structural springs in order to provide shear strain force and guarantee stability on the original shape formation. One has to use his a priori knowledge or trial-anderror method to construct a stable spring network for a given deformable object. This is due to the inherent one-dimensional nature of the conventional spring model. In order to overcome the difficulty in designing a spring network and make it possible to construct a stable network easily and intuitively, we propose an oriented particle and generalized spring model that reacts against bending and twisting force as well as stretching. By using our new mass-spring system, one can easily construct a spring network from a given geometric model. Moreover, one can animate one-dimensional flexible object such as a mobile as well as a thin twodimensional object with sharp folds or creases. In addition, we present an offsetting method for tweaking mass-spring system to have valuable properties that help animating deformable objects with various shapes.
Packing Square Tiles into One Texture
(Eurographics Association, 2004) Decaudin, Philippe; Neyret, Fabrice; M. Alexa and E. Galin
This paper deals with the packing of square tiles of the same size into one texture. Texture size is constrained by the graphics hardware. In particular, width and height resolutions must be powers of two. To cover the whole texture and avoid space loss, common schemes pack a number of tiles that is a power of two. We show that numbers of tiles like 5, 13, 17, 25, 34 and others can also be reached without wasting memory. To achieve this, our scheme takes advantage of texture rotation and the wrapping capability of texture-addressing, which gives a torus topology to the texture space.
A Quick and Automatic Image Based Modeling and Rendering System
(Eurographics Association, 2004) Yerex, Keith; Birkbeck, Neil; Cobzas, Dana; Jagersand, Martin; M. Alexa and E. Galin
We present a complete and automatic system for object capture from video, Internet delivery, and real-time photorealistic rendering. Shape from silhouette is used to capture an approximate enveloping geometry, the visual hull. Texture coordinates are generated automatically under a minimum distortion criterion. To account for the difference between the true shape of the object and the captured visual hull we use Dynamic texturing, a viewdependent texturing method, which explicitly captures geometric deviations and applies a texture based correction. These models are then efficiently coded, and delivered over the Internet.
A Real Time Light Probe
(Eurographics Association, 2004) Unger, Jonas; Gustavson, Stefan; Ollila, M.; Johannesson, M.; M. Alexa and E. Galin
We present a novel system capable of capturing high dynamic range (HDR) Light Probes at video speed. Each Light Probe frame is built from an individual full set of exposures, all of which are captured within the frame time. The exposures are processed and assembled into a mantissa-exponent representation image within the camera unit before output, and then streamed to a standard PC. As an example, the system is capable of capturing Light Probe Images with a resolution of 512x512 pixels using a set of 10 exposures covering 15 f-stops at a frame rate of up to 25 final HDR frames per second. The system is built around commercial special-purpose camera hardware with on-chip programmable image processing logic and tightly integrated frame buffer memory, and the algorithm is implemented as custom downloadable microcode software.
Realtime Isosurface Extraction with Graphics Hardware
(Eurographics Association, 2004) Reck, Frank; Dachsbacher, Carsten; Grosso, Roberto; Greiner, Günther; Stamminger, Marc; M. Alexa and E. Galin
In this paper we introduce a method for the display of isosurfaces extracted from unstructured tetrahedral grids. Our algorithm completely runs on the graphics hardware. The tetrahedra are streamed into a vertex program, which extracts the surface for the given isovalue and immediately renders it. The triangles are not stored explicitly but are computed during rendering time, so the user can modify the isovalue with immediate feedback. If the tetrahedra entirely fit into video memory, we achieve a throughput of more than nine million tetrahedra per second. Our performance can be further improved by using a hybrid method which pre-selects tetrahedra containing the isovalue. We compare our approach with a pure CPU based implementation which achieves about half the performance of our hardware accelerated method.
Region Completion in a Single Image
(Eurographics Association, 2004) Zhang, Yunjun; Xiao, Jiangjian; Shah, Mubarak; M. Alexa and E. Galin
Natural images and Photographs sometimes may contain stains or undesired objects covering significant portions of the images. Region completion is a method to fill in such significant portions of an image by using the information from the remaining area of the image. We propose a novel approach to achieve the completion in three steps. First, a spatial-range model is determined to establish the searching order of the target patch. Second, a source patch is selected by measuring the adjusted appearance of the source patch with the target patch and enforcing the searching area in the neighborhood around the previous source patch. Third, a graphcut patch updating algorithm is designed to ensure the non-blurring updating. A number of examples are given to demonstrate the effectiveness of our method.
SP-Octrees Visualization Using Impostors
(Eurographics Association, 2004) Melero Rus, Francisco J.; Cano Olivares, Pedro; Torres Cantero, Juan Carlos; M. Alexa and E. Galin
SP-Octrees (Space-Partition Octrees) allow a multiresolution representation of polyhedral objects, and have been successfully used in progressive transmission. Nonetheless, the SP-Octree is a solid modeling structure, intended to solve problems as solid intersections and point inclusion tests. At intermediate levels of the SP-Octree, the visualization is a rough approximation of the object due to the fact that grey nodes are shown as the convex hull of the part of the solid included in that node. In this paper we present an approach to use SP-Octrees for adaptative visualization, that improves the visualization of these multiresolution models by applying impostors over those planes of the hierarchical structure that belongs to the convex hull but are not part of the solid boundary (ficticious planes). By doing so, it is possible to obtain a better approximating visualization of the object, although the maximum LOD is not used. At every moment, the impostor is selected depending on the viewpoint.
A Spectral Gamut-Mapping Environment with Rendering Parameter Feedback
(Eurographics Association, 2004) Bell, Ian E.; Alexander, Simon K.; M. Alexa and E. Galin
This paper proposes a prototypical environment for gamut mapping in spectral space. Images are rendered in terms of light and material parameters by a symbolic ray tracer, and the parameter ranges are adjusted, without re-rendering, to bring the image into the output device's spectral gamut. There is a growing disparity between the high dynamic range images produced by spectral renderers and the limitations of display gamuts and lowdimensional colour management standards. While in rendering tone mapping has helped compress luminance ranges, and in colour science 3D gamut mapping has helped compress chrominance ranges, only high-dimensional spectral methods will fully bridge the gap. This paper's environment for gamuts in spectral space is a step toward spectral gamut mapping, which we demonstrate by using the ray tracer to predict feasible ranges of rendering parameters for an in-gamut image. The environment can be easily extended to support interactive or automatic image correction, and more sophisticated rendering and gamut-mapping methods of arbitrary dimensionality.
Steerable Texture Synthesis
(Eurographics Association, 2004) Taponecco, Francesca; Alexa, Marc; M. Alexa and E. Galin
Texture synthesis is typically concerned with the creation of an arbitrarily sized texture from a small sample, where the pattern of the generated texture should be perceived as resembling the example. Most of the current work follows a Markov model approach. The texture is generated by finding best matching pixels or patches in the sample and then copying them to the target. Here we extend this concept to incorporate arbitrary filters acting on the sample before matching and transferring. The filters may vary over the generated texture. Steering the filters with properties connected to the output image allows generating a variety of effects.
Tone Mapping in VR Environments
(Eurographics Association, 2004) Hausner, Alexander; Stamminger, Marc; M. Alexa and E. Galin
Tone mapping is the process of mapping high dynamic range images to the low dynamic range of current displays. So far, tone mapping research was focused on static images, but with powerful graphics hardware available today, real time tone mapping becomes possible. In this paper we describe tone mapping within a VR environment. The tone mapping operator utilizes information about the user's line of sight obtained by a tracking system. Adaptation is optimized for the current view point and costly image operations are restricted to the central view field. Since all computations are completely performed by graphics hardware, we achieve interactive frame rates.
Uniform Sampling for Image-based Rendering Shiny Objects
(Eurographics Association, 2004) Gong, Minglun; Yang, Yee-Hong; M. Alexa and E. Galin
A novel sampling technique is presented, which can evenly sample all rays that pass through a rectangular surface. Different view directions are uniformly sampled based on the shape of a spiral. Projection positions are then sampled adaptively according to the view direction to provide a constant sampling rate. The experimental results show that our approach can faithfully represent shiny real objects with a reasonable number of samples.

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