Developable surfaces have many desired properties in manufacturing process. Since most existing CAD systems utilize parametric surfaces as the design primitive, there is a great demand in industry to convert a parametric surface within a prescribed global error bound into developable patches. In this work we propose a simple and efficient solution to approximate a general parametric surface with a minimum set of C0-joint developable strips. The key contribution of the proposed algorithm is that, several global optimization problems are elegantly solved in a sequence that offers a controllable global error bound on the developable surface approximation. Experimental results are presented to demonstrate the effectiveness and stability of the proposed algorithm.
In this paper, we introduce an interactive tool for local color transfer. The new technique is based on the observation that color transfer operations are local in nature while at the same time should adhere global consistency. We introduce a brush by which the user specifies the source and destination image regions for color transfer. Color statistics in the source region are transferred to the destination region. A global optimization is then applied to eliminate vi- sual discontinuities that may result by the local operations. We demonstrate that our tool is easy to use yet effective in quickly generating diverse artistic effects.
A technology for automatically creating and adding the sound to interactive CG animations of spark discharges in real time has been developed. In the procedure proposed in this paper, the user inputs the electric charge distribution, boundary conditions and other parameters affecting the initiation of electric discharges in virtual space. The animation of the discharge is then created by generating the shape of the discharge pattern and rendering it, and the sound synchronized with the animation is automatically generated in real time. The noises from spark discharges are shock waves, which exhibit complicated behavior; but, in this study, an empirical shape for a shock wave is employed to efficiently generate the acoustic waveform. Effective procedures for expressing lightning discharges and continuous discharges are also proposed.
Interactive animation systems often use a level-of-detail (LOD) control to reduce the computational cost by eliminating unperceivable details of the scene.Most methods employ a multiresolutional representation of animation and geometrical data, and adaptively change the accuracy level according to the importance of each character.Multilinear analysis provides the efficient representation of multidimensional and multimodal data, including human motion data, based on statistical data correlations.This paper proposes a LOD control method of motion synthesis with a multilinear model.Our method first extracts a small number of principal components of motion samples by analyzing three-mode correlations among joints, time, and samples using high-order singular value decomposition.A new motion is synthesized by interpolating the reduced components using geostatistics, where the prediction accuracy of the resulting motion is controlled by adaptively decreasing the data dimensionality.We introduce a hybrid algorithm to optimize the reduction size and computational time according to the distance from the camera while maintaining visual quality.Our method provides a practical tool for creating an interactive animation of many characters while ensuring accurate and flexible controls at a modest level of computational cost.
We present a data-driven approach to build a human body model from a single photograph by performing Principal Component Analysis (PCA) on a database of body segments. We segment a collection of human bodies to compile the required database prior to performing the analysis. Our approach then builds a single PCA for each body segment - head, left and right arms, torso and left and right legs - yielding six PCAs in total. This strategy improves on the flexibility of conventional data-driven approaches in 3D modeling and allows our approach to take variations in ethnicity, age and body posture into account. We demonstrate our approach in practice by constructing models of a Caucasian male, an Asian male and a toddler from corresponding photographs and a Caucasian adult oriented database. We also discuss rapid consistent parameterization based on Radial Basis Functions (RBF) and non-optimization based learning systems to reduce execution time.
We present a Delaunay based algorithm for simplifying vector field datasets. Our aim is to reduce the size of the mesh on which the vector field is defined while preserving topological features of the original vector field. We leverage a simple paradigm, vertex deletion in Delaunay triangulations, to achieve this goal. This technique is effective for two reasons. First, we guide deletions by a local error metric that bounds the change of the vectors at the affected simplices and maintains regions near critical points to prevent topological changes. Second, piecewise-linear interpolation over Delaunay triangulations is known to give good approximations of scalar fields. Since a vector field can be regarded as a collection of component scalar fields, a Delaunay triangulation can preserve each component and thus the structure of the vector field as a whole. We provide experimental evidence showing the effectiveness of our technique and its ability to preserve features of both two and three dimensional vector fields.
We propose a technique for fusing a bracketed exposure sequence into a high quality image, without converting to HDR first. Skipping the physically-based HDR assembly step simplifies the acquisition pipeline. This avoids camera response curve calibration and is computationally efficient. It also allows for including flash images in the sequence. Our technique blends multiple exposures, guided by simple quality measures like saturation and contrast. This is done in a multiresolution fashion to account for the brightness variation in the sequence. The resulting image quality is comparable to existing tone mapping operators.
Video matting is the process of taking a sequence of frames, isolating the foreground, and replacing the background in each frame. We look at existing single-frame matting techniques and present a method that improves upon them by adding depth information acquired by a time-offlight range scanner. We use the depth information to automate the process so it can be practically used for video sequences. In addition, we show that we can improve the results from natural matting algorithms by adding a depth channel. The additional depth information allows us to reduce the artifacts that arise from ambiguities that occur when an object is a similar color to its background.
In this paper we propose a new volumetric implicit surface data structure as an alternative representation to perform mesh processing algorithms. We introduce a new triangulation algorithm suitable for our voxel-based volumetric structure which is a vector field distance transform from an explicit mesh. This new representation is an extension of the implicit scalar field distance function of a mesh. We show our new vector field function is more accurate than the classic scalar field function by comparing both representations with an error metric evaluation. We adapt to this new vector representation mesh integration operation in the reconstruction process of 3D objects from scanned data which was previously performed on the implicit scalar field function. Results show that using this new vector field representation, our mesh integration and mesh triangulation algorithm designs outperform the previous processes based on the implicit scalar field function representation.
Skinned Mesh Animation (SMA) well approximates a mesh animation with extracted bones and their transformations. However, unlike skeleton, bones in SMA are not organized in hierarchies, thus they need mesh dependent translation vectors which prevent other sources of motion (i.e. skeletal animations, MoCAP, SMAs etc) from being applied to the skinned mesh. In this paper, we propose a new and fast method to transplant motion to skinned meshes. By efficiently solving a linear least-squares system, we can compute new translation vectors which enable the motion to work on the skinned mesh. Based on the same idea, we have also devised a SMA editing tool which allows users to edit frames of the SMA interactively. Furthermore, the editing can be propagated to all subsequent frames.
In this paper we present a technique for image deformation in which the user is given flexible control over what kind of deformation to perform. Freeform image extends available image deformation techniques in that it provides a palette of intuitive tools including interactive ob- ject segmentation, stiffness editing and force-based controls to achieve both a natural look and realistic animations of deforming parts. The model underlying our approach is physics-based and it is amenable to a variety of different kinds of image manipulations ranging from as-rigid-as-possible to fully elastic deformations. We have developed a multigrid solver for quadrangular finite elements, which achieves real-time performance for high resolution pixel grids. On recent CPUs this solver can handle about 16K co-rotated finite elements at roughly 60 ms.
We describe a computer graphics system that supports conceptual architectural design and analysis. We use as a starting point the traditional sketchbook drawings that architects use to experiment with various views, sections, and details. Rather than interpret or infer 3D structure from drawings, our system is designed to allow the designer to organize concept drawings in 3D, and gradually fuse a series of possibly geometrically-inconsistent sketches into a set of 3D strokes. Our system uses strokes and planar "canvases" as basic primitives; the basic mode of input is traditional 2D drawing. We introduce methods for the user to control stroke visibility and transfer strokes between canvases. We also introduce methods for the user to position and orient the canvases that have infinite extent. We demonstrate the use of the system to analyze existing structures and conceive new designs.
Mesh editing methods based on differential surface representations are known for their efficiency and ease of implementation. For reconstruction from such representations, local frames have to be determined which is a non-linear problem. In linear approximations frames can either degenerate or become inconsistent with the geometry. Both results in contra-intuitive deformations. Existing non-linear approaches, however are comparatively slow and considerably more complex. In this paper we present a differential representation that implicitly enforces orthogonal and geometry consistent frames while allowing a simple and efficient implementation. In particular, it enforces conformal surface deformations preserving local texture features.
In 3D computer graphics, mesh parameterization is a key technique for digital geometry processings(DGP) such as morphing, shape blending, texture transfer, re-meshing and so on. This paper proposes a novel approach for parameterizing a mesh into another one directly. The main idea of our method is to combine a competitive learning and a leastsquare mesh techniques. It is enough to give some semantic feature correspondences between target meshes, even if they are in different shapes or in different poses. We show the effectiveness of our approach by giving some examples of its applications.
We present an appearance-based user interface for artists to efficiently design customized image-based lighting environments. 1 Our approach avoids typical iterations of parameter editing, rendering, and confirmation by providing a set of intuitive user interfaces for directly specifying the desired appearance of the model in the scene. Then the system automatically creates the lighting environment by solving the inverse shading problem. To obtain a realistic image, all-frequency lighting is used with a spherical radial basis function (SRBF) representation. Rendering is performed using precomputed radiance transfer (PRT) to achieve a responsive speed. User experiments demonstrated the effectiveness of the proposed system compared to a previous approach.
In this paper, we present a new and efficient spherical harmonics decomposition for spherical functions defining 3D triangulated objects. Such spherical functions are intrinsically associated to star-shaped objects. However our results can be extended to any triangular object after segmentation into star-shaped surface patches and recomposition of the results in the implicit framework. There is thus no restriction about the genus number of the object. We demonstrate that the evaluation of the spherical harmonics coefficients can be performed by a Monte Carlo integration over the edges, which makes the computation more accurate and faster than previous techniques, and provides a better control over the precision error in contrast to the voxel-based methods. We present several applications of our research, including fast spectral surface reconstruction from point clouds, local surface smoothing and interactive geometric texture transfer.
We present an approach to define shape deformations by constructing and interactively modifying C 1 continuous time-dependent divergence-free vector fields. The deformation is obtained by a path line integration of the mesh vertices. This way, the deformation is volume-preserving, free of (local and global) self-intersections, feature preserving, smoothness preserving, and local. Different modeling metaphors support the approach which is able to modify the vector field on-the-fly according to the user input. The approach works at interactive frame rates for moderate mesh sizes, and the numerical integration preserves the volume with a high accuracy.
Rendering global illumination effects for dynamic scenes at interactive frame rates is a computationally challenging task. Much of the computation time needed is spent during visibility queries between individual scene elements, and it is almost illusive to update this information at realtime even for moderately complex scenes. In this paper, we propose a global illumination approach for dynamic scenes that runs at near-real-time frame rates on a single PC. Our method is inspired by the principles of hierarchical radiosity and tackles the visibility problem by implicitly evaluating mutual visibility while constructing a hierarchical link structure between scene elements. By means of the same efficient and easy-to-implement framework, we are able to reproduce a large variety of complex lighting effects for moderately sized scenes, such as interreflections, environment map lighting as well as area light sources.
This paper presents an image-space approximation technique for real-time subsurface scattering. We first create transmitted irradiance samples on shadow maps and then estimate single scattering efficiently using a method similar to shadow mapping, with adaptive deterministic sampling. We incorporate this single-scattering with a recently proposed technique for multiple scattering. We demonstrate that our technique produces high-quality images of animated scenes. We archived hundreds of frames per second on graphics hardware without lengthy preprocessing.
We describe a new algorithm for the visualisation of implicit algebraic curves, which isolates the singular points, compute the topological degree around these points in order to check that the topology of the curve can be deduced from the points on the boundary of these singular regions. The other regions are divided into x or y regular regions, in which the branches of the curve are also determined from information on the boundary. Combined with enveloping techniques of the polynomial represented in the Bernstein basis, it is shown on examples that this algorithm is able to render curves defined by high degree polynomials with large coefficients, to identify regions of interest and to zoom safely on these regions.
