Accelerating the Rendering Process Using Impostors

Stefan Jeschke
Accelerating the Rendering Process Using Impostors
Supervisor: Heidrun Schumann
Duration: 2002-2005
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Abstract

The interactive rendering of three-dimensional geometric models is a research area of big interest in computer graphics. The generation of a fluent animation for complex models, consisting of multiple million primitives, with more than 60 frames per second is a special challenge. Possible applications include ship-, driving- and flight simulators, virtual reality and computer games. Although the performance of common computer graphics hardware has dramatically increased in recent years, the demand for more realism and complexity in common scenes is growing even faster. This dissertation is about one approach for accelerating the rendering of such complex scenes. We take advantage of the fact that the appearance of distant scene parts hardly changes for several successive output images. Those scene parts are replaced by precomputed image-based representations, so-called impostors. Impostors are very fast to render while maintaining the appearance of the scene part as long as the viewer moves within a bounded viewing region, a so-called view cell. However, unsolved problems of impostors are the support of a satisfying visual quality with reasonable computational effort for the impostor generation, as well as very high memory requirements for impostors for common scenes. Until today, these problems are the main reason why impostors are hardly used for rendering acceleration. This thesis presents two new impostor techniques that are based on partitioning the scene part to be represented into image layers with different distances to the observer. A new error metric allows a guarantee for a minimum visual quality of an impostor even for large view cells. Furthermore, invisible scene parts are efficiently excluded from the representation without requiring any knowledge about the scene structure, which provides a more compact representation. One of the techniques combines every image layer separately with geometric information. This allows a fast generation of memory-efficient impostors for distant scene parts. In the other technique, the geometry is independent from the depth layers, which allows a compact representation for near scene parts. The second part of this work is about the efficient usage of impostors for a given scene. The goal is to guarantee a minimum frame rate for every view within the scene while at the same time minimizing the memory requirements for all impostors. The presented algorithm automatically selects impostors and view cells so that for every view, only the most suitable scene parts are represented as impostors. Previous approaches generated numerous similar impostors for neighboring view cells, thus wasting memory. The new algorithm overcomes this problem. i The simultaneous use of additional acceleration techniques further reduces the required impostor memory and allows making best use of all available techniques at the same time. The approach is general in the sense that it can handle arbitrary scenes and a broad range of impostor techniques, and the acceleration provided by the impostors can be adapted to the bottlenecks of different rendering systems. In summary, the provided techniques and algorithms dramatically reduce the required impostor memory and simultaneously guarantee a minimum output image quality. This makes impostors useful for numerous scenes and applications where they could hardly be used before.

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BibTeX

@phdthesis{jeschke-05-ARI,
  title =      "Accelerating the Rendering Process Using Impostors",
  author =     "Stefan Jeschke",
  year =       "2005",
  abstract =   "The interactive rendering of three-dimensional geometric
               models is a research area of big interest in computer
               graphics. The generation of a fluent animation for complex
               models, consisting of multiple million primitives, with more
               than 60 frames per second is a special challenge. Possible
               applications include ship-, driving- and flight simulators,
               virtual reality and computer games. Although the performance
               of common computer graphics hardware has dramatically
               increased in recent years, the demand for more realism and
               complexity in common scenes is growing even faster. This
               dissertation is about one approach for accelerating the
               rendering of such complex scenes. We take advantage of the
               fact that the appearance of distant scene parts hardly
               changes for several successive output images. Those scene
               parts are replaced by precomputed image-based
               representations, so-called impostors. Impostors are very
               fast to render while maintaining the appearance of the scene
               part as long as the viewer moves within a bounded viewing
               region, a so-called view cell. However, unsolved problems of
               impostors are the support of a satisfying visual quality
               with reasonable computational effort for the impostor
               generation, as well as very high memory requirements for
               impostors for common scenes. Until today, these problems are
               the main reason why impostors are hardly used for rendering
               acceleration. This thesis presents two new impostor
               techniques that are based on partitioning the scene part to
               be represented into image layers with different distances to
               the observer. A new error metric allows a guarantee for a
               minimum visual quality of an impostor even for large view
               cells. Furthermore, invisible scene parts are efficiently
               excluded from the representation without requiring any
               knowledge about the scene structure, which provides a more
               compact representation. One of the techniques combines every
               image layer separately with geometric information. This
               allows a fast generation of memory-efficient impostors for
               distant scene parts. In the other technique, the geometry is
               independent from the depth layers, which allows a compact
               representation for near scene parts. The second part of this
               work is about the efficient usage of impostors for a given
               scene. The goal is to guarantee a minimum frame rate for
               every view within the scene while at the same time
               minimizing the memory requirements for all impostors. The
               presented algorithm automatically selects impostors and view
               cells so that for every view, only the most suitable scene
               parts are represented as impostors. Previous approaches
               generated numerous similar impostors for neighboring view
               cells, thus wasting memory. The new algorithm overcomes this
               problem. i The simultaneous use of additional acceleration
               techniques further reduces the required impostor memory and
               allows making best use of all available techniques at the
               same time. The approach is general in the sense that it can
               handle arbitrary scenes and a broad range of impostor
               techniques, and the acceleration provided by the impostors
               can be adapted to the bottlenecks of different rendering
               systems. In summary, the provided techniques and algorithms
               dramatically reduce the required impostor memory and
               simultaneously guarantee a minimum output image quality.
               This makes impostors useful for numerous scenes and
               applications where they could hardly be used before.",
  month =      mar,
  address =    "Favoritenstrasse 9-11/186, A-1040 Vienna, Austria",
  school =     "Institute of Computer Graphics and Algorithms, Vienna
               University of Technology",
  keywords =   "image-based rendering, impostors, rendering acceleration",
  URL =        "https://www.cg.tuwien.ac.at/research/publications/2005/jeschke-05-ARI/",
}