Stefan Jeschke

A GPU Laplacian solver for diffusion curves and Poisson image editing

We present a new Laplacian solver for minimal surfaces---surfaces having a mean curvature of zero everywhere except at some fixed (Dirichlet) boundary conditions. Our solution has two main contributions: First, we provide a robust rasterization technique to transform continuous boundary values (diffusion curves) to a discrete domain. Second, we define a variable stencil size diffusion solver that solves the minimal surface problem. We prove that the solver converges to the right solution, and demonstrate that it is at least as fast as commonly proposed multigrid solvers, but much simpler to implement. It also works for arbitrary image resolutions, as well as 8 bit data. We show examples of robust diffusion curve rendering where our curve rasterization and diffusion solver eliminate the strobing artifacts present in previous methods. We also show results for real-time seamless cloning and stitching of large image panoramas.

Dart throwing on surfaces

In this paper we present dart throwing algorithms to generate maximal Poisson disk point sets directly on 3D surfaces. We optimize dart throwing by efficiently excluding areas of the domain that are already covered by existing darts. In the case of triangle meshes, our algorithm shows dramatic speed improvement over comparable sampling methods. The simplicity of our basic algorithm naturally extends to the sampling of other surface types, including spheres, NURBS, subdivision surfaces, and implicits. We further extend the method to handle variable density points, and the placement of arbitrary ellipsoids without overlap. Finally, we demonstrate how to adapt our algorithm to work with geodesic instead of Euclidean distance. Applications for our method include fur modeling, the placement of mosaic tiles and polygon remeshing.

Pixel-correct shadow maps with temporal reprojection and shadow test confidence

Shadow mapping suffers from spatial aliasing (visible as blocky shadows) as well as temporal aliasing (visible as flickering). Several methods have already been proposed for reducing such artifacts, but so far none is able to provide satisfying results in real time. This paper extends shadow mapping by reusing information of previously rasterized images, stored efficiently in a so-called history buffer. This buffer is updated in every frame and then used for the shadow calculation. In combination with a special confidence-based method for the history buffer update (based on the current shadow map), temporal and spatial aliasing can be completely removed. The algorithm converges in about 10 to 60 frames and during convergence, shadow borders are sharpened over time. Consequently, in case of real-time frame rates, the temporal shadow adaption is practically imperceptible. The method is simple to implement and is as fast as uniform shadow mapping, incurring only the minor speed hit of the history buffer update. It works together with advanced filtering methods like percentage closer filtering and more advanced shadow mapping techniques like perspective or light space perspective shadow maps.

Textured depth meshes for real-time rendering of arbitrary scenes

This paper presents a new approach to generate textured depth meshes (TDMs), an impostor-based scene representation that can be used to accelerate the rendering of static polygonal models. The TDMs are precalculated for a fixed viewing region (view cell).The approach relies on a layered rendering of the scene to produce a voxel-based representation. Secondary, a highly complex polygon mesh is constructed that covers all the voxels. Afterwards, this mesh is simplified using a special error metric to ensure that all voxels stay covered. Finally, the remaining polygons are resampled using the voxel representation to obtain their textures.The contribution of our approach is manifold: first, it can handle polygonal models without any knowledge about their structure. Second, only scene parts that may become visible from within the view cell are represented, thereby cutting down on impostor complexity and storage costs. Third, an error metric guarantees that the impostors are practically indistinguishable compared to the original model (i.e. no rubber-sheet effects or holes appear as in most previous approaches). Furthermore, current graphics hardware is exploited for the construction and use of the impostors.

Route Visualization Using Detail Lenses

We present a method designed to address some limitations of typical route map displays of driving directions. The main goal of our system is to generate a printable version of a route map that shows the overview and detail views of the route within a single, consistent visual frame. Our proposed visualization provides a more intuitive spatial context than a simple list of turns. We present a novel multifocus technique to achieve this goal, where the foci are defined by points of interest (POI) along the route. A detail lens that encapsulates the POI at a finer geospatial scale is created for each focus. The lenses are laid out on the map to avoid occlusion with the route and each other, and to optimally utilize the free space around the route. We define a set of layout metrics to evaluate the quality of a lens layout for a given route map visualization. We compare standard lens layout methods to our proposed method and demonstrate the effectiveness of our method in generating aesthetically pleasing layouts. Finally, we perform a user study to evaluate the effectiveness of our layout choices.

Rendering surface details with diffusion curves

Diffusion curve images (DCI) provide a powerful tool for efficient 2D image generation, storage and manipulation. A DCI consist of curves with colors defined on either side. By diffusing these colors over the image, the final result includes sharp boundaries along the curves with smoothly shaded regions between them. This paper extends the application of diffusion curves to render high quality surface details on 3D objects. The first extension is a view dependent warping technique that dynamically reallocates texture space so that object parts that appear large on screen get more texture for increased detail. The second extension is a dynamic feature embedding technique that retains crisp, anti-aliased curve details even in extreme closeups. The third extension is the application of dynamic feature embedding to displacement mapping and geometry images. Our results show high quality renderings of diffusion curve textures, displacements, and geometry images, all rendered interactively.

Interactive smooth and curved shell mapping

Shell mapping is a technique to represent three-dimensional surface details. This is achieved by extruding the triangles of an existing mesh along their normals, and mapping a 3D function (e.g., a 3D texture) into the resulting prisms. Unfortunately, such a mapping is nonlinear. Previous approaches perform a piece-wise linear approximation by subdividing the prisms into tetrahedrons. However, such an approximation often leads to severe artifacts. In this paper we present a correct (i.e., smooth) mapping that does not rely on a decomposition into tetrahedrons. We present an efficient GPU ray casting algorithm which provides correct parallax, self-occlusion, and silhouettes, at the cost of longer rendering times. The new formulation also allows modeling shells with smooth curvatures using Coons patches within the prisms. Tangent continuity between adjacent prisms is guaranteed, while the mapping itself remains local, i.e. every curved prism content is modeled at runtime in the GPU without the need for any precomputation. This allows instantly replacing animated triangular meshes with prism-based shells.

Estimating Color and Texture Parameters for Vector Graphics

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.

Automatic impostor placement for guaranteed frame rates and low memory requirements

Impostors are image-based primitives commonly used to replace complex geometry in order to reduce the rendering time needed for displaying complex scenes. However, a big problem is the huge amount of memory required for impostors. This paper presents an algorithm that automatically places impostors into a scene so that a desired frame rate and image quality is always met, while at the same time not requiring enormous amounts of impostor memory. The low memory requirements are provided by a new placement method and through the simultaneous use of other acceleration techniques like visibility culling and geometric levels of detail.

Image-based Representations for Accelerated Rendering of Complex Scenes.

This paper gives an overview of image-based representations commonly used for reducing the geometric complexity of a scene description in order to accelerate the rendering process. Several different types of representations and ways for using them have been presented, which are classified and discussed here. Furthermore, the overview includes techniques for accelerating the rendering of static scenes or scenes with animations and/or dynamic lighting effects. The advantages and drawbacks of the different approaches are illuminated, and unsolved problems and roads for further research are shown.