A Survey of Nonlinear Prefiltering Methods for Efficient and Accurate Surface Shading <s> Mesh Prefiltering <s> A method is described for switching smoothly between rendering algorithms as required by the amount of visible surface detail. The result will be more realism with less computation for displaying objects whose surface detail can be described by one or more bump maps. The three rendering algorithms considered are a BRDF, bump mapping, and displacement mapping. The bump mapping has been modified to make it consistent with the other two. For a given viewpoint, one of these algorithms will show a better trade-off between quality, computation time, and aliasing than the other two. The decision as to which algorithm is appropriate is a function of distance, viewing angle, and the frequency of bumps in the bump map. <s> BIB001 </s> A Survey of Nonlinear Prefiltering Methods for Efficient and Accurate Surface Shading <s> Mesh Prefiltering <s> A growing number of real-time applications need graphics with photorealistic quality, especially in the field of training (virtual operation, driving and flightsimulation), but also in the areas of design or ergonomic research. We take a closer look at main deficiencies of today's real time graphics hardware and present solutions for several of the identified problems in the areas of antialiasing and texture-, bumpand reflection mapping. In the second part of the paper, a new method for antialiasing bump maps is explained in more detail. CR Categories and Subject Desscriptors: I.3.1 [Computer Graphics]: Hardware Architecture – Graphics Processors, Raster Display Devices; I.3.3 [Computer Graphics]: Picture/Image generation. Additional <s> BIB002 </s> A Survey of Nonlinear Prefiltering Methods for Efficient and Accurate Surface Shading <s> Mesh Prefiltering <s> Abstract In many applications the need for an accurate simplification of surface meshes is becoming more and more urgent. This need is not only due to rendering speed reasons, but also to allow fast transmission of 3D models in network-based applications. Many different approaches and algorithms for mesh simplification have been proposed in the last few years. We present a survey and a characterization of the fundamental methods. Moreover, the results of an empirical comparison of the simplification codes available in the public domain are discussed. Five implementations, chosen to give a wide spectrum of different topology preserving methods, were run on a set of sample surfaces. We compared empirical computational complexities and the approximation accuracy of the resulting output meshes. <s> BIB003 </s> A Survey of Nonlinear Prefiltering Methods for Efficient and Accurate Surface Shading <s> Mesh Prefiltering <s> Rendering high quality digital terrains at interactive rates requires carefully crafted algorithms and data structures able to balance the competing requirements of realism and frame rates, while taking into account the memory and speed limitations of the underlying graphics platform. In this survey, we analyze multiresolution approaches that exploit a certain semi-regularity of the data. These approaches have produced some of the most efficient systems to date. After providing a short background and motivation for the methods, we focus on illustrating models based on tiled blocks and nested regular grids, quadtrees and triangle bin-trees triangulations, as well as cluster-based approaches. We then discuss LOD error metrics and system-level data management aspects of interactive terrain visualization, including dynamic scene management, out-of-core data organization and compression, as well as numerical accuracy. <s> BIB004 </s> A Survey of Nonlinear Prefiltering Methods for Efficient and Accurate Surface Shading <s> Mesh Prefiltering <s> Realistic animation and rendering of the ocean is an important aspect for simulators, movies and video games. By nature, the ocean is a difficult problem for Computer Graphics: it is a dynamic system, it combines wave trains at all scales, ranging from kilometric to millimetric. Worse, the ocean is usually viewed at several distances, from very close to the viewpoint to the horizon, increasing the multi-scale issue, and resulting in aliasing problems. The illumination comes from natural light sources (the Sun and the sky dome), is also dynamic, and often underlines the aliasing issues. In this paper, we present a new algorithm for modelling, animation, illumination and rendering of the ocean, in real-time, at all scales and for all viewing distances. Our algorithm is based on a hierarchical representation, combining geometry, normals and BRDF. For each viewing distance, we compute a simplified version of the geometry, and encode the missing details into the normal and the BRDF, depending on the level of detail required. We then use this hierarchical representation for illumination and rendering. Our algorithm runs in real-time, and produces highly realistic pictures and animations. <s> BIB005 </s> A Survey of Nonlinear Prefiltering Methods for Efficient and Accurate Surface Shading <s> Mesh Prefiltering <s> Whilst the Deep Shadow Maps algorithm for accelerating the rendering of volumetric shadows is a fitting solution for offline applications, it can consume an unbounded amount of memory and is difficult to map well to current graphics hardware. For these reasons alternative methods have been proposed for interactive applications based on the idea of accumulating opacity from volume primitives in depth-based buckets or slices. However, these slice-based methods can introduce objectionable and unstable slice-like artefacts due to undersampling of the depth range, and often many slices are required to overcome these artefacts. Further refinements have been proposed to address this, but they constrain the generality of the algorithm, for example by mandating an assumption of uniform opacity or by dropping support for pre-filtering. We introduce a novel algorithm called Fourier Opacity Mapping (FOM) and we show that it is a good choice for rendering artefact-free pre-filtered volumetric shadows in cases where spatial opacity variations are smooth (e.g. smoke, gas and low-opacity hair). We also show how the algorithm can be generalised to other orthonormal bases. <s> BIB006
The above silhouette and curvature problems are particular cases of a more general problem cited in the introduction, namely, that prefiltering the coarse mesh and its maps separately is inaccurate. Some mesh simplification algorithms take the maps into account to ensure that parallax errors introduced by the simplification step remain under a given threshold (see BIB003 and  for a survey of the mesh simplification algorithms, and BIB004 for the specific case of terrains). This is necessary but not . Performance in frames per second and scalars per texel (for 800 Â 800 images on an NVidia GeForce GTX 470). Ground truth images for a plane (orange frames) and for the complex surface S of Fig. 1 (red frames) are computed with a numerical integration of (1) with a Lanczos filter w. sufficient: the mesh details removed by the simplification must also be incorporated in the maps. Here, the methods proposed by Becker and Max BIB001 and Schilling BIB002 could be inspiring, although they start from a bump map instead of a mesh, as well as the ocean filtering method of Bruneton et al. BIB005 . Finally, at large distances or very grazing angles, when the simplified mesh becomes very different from the complex surface, it may become impossible to represent this surface with view-independent maps (e.g., the foliage of a tree cannot be defined with view-independent maps defined on an enclosing ellipsoid). At this stage, instead of using view-dependent surface maps, switching to a volumetric representation may be more appropriate. But this opens a new problem, out of the scope of this paper, namely, the prefiltering of volumetric data used in a nonlinear way for rendering (e.g., BIB006 ).