Efficient Irradiance Normal Mapping

Ralf Habel, Michael Wimmer
Efficient Irradiance Normal Mapping
In Proceedings of the ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games 2010, pages 189-195. February 2010.
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Abstract

Irradiance normal mapping is a method to combine two popular techniques, light mapping and normal mapping, and is used in games such as Half-Life 2 or Halo 3. This combination allows using low-resolution light caching on surfaces with only a few coefficients which are evaluated by normal maps to render spatial high-frequency changes in the lighting. Though there are dedicated bases for this purpose such as the Half-Life 2 basis, higher order basis functions such as quadratic Spherical Harmonics are needed for an accurate representation. However, a full spherical basis is not needed since the irradiance is stored on the surface of a scene.

In order to represent the irradiance signals efficiently, we propose a novel polynomial, hemispherically orthonormal basis function set that is specifically designed to carry a directional irradiance signal on the hemisphere and which makes optimal use of the number of coefficients. To compare our results with previous work, we analyze the relations and attributes of previously proposed basis systems and show that 6 coefficients are sufficient to accurately represent an irradiance signal on the hemisphere. To create the necessary irradiance signals, we use Spherical Harmonics as an intermediate basis due to their fast filtering capabilities.

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BibTeX

@inproceedings{Habel-2010-EIN,
  title =      "Efficient Irradiance Normal Mapping",
  author =     "Ralf Habel and Michael Wimmer",
  year =       "2010",
  abstract =   "Irradiance normal mapping is a method to combine two popular
               techniques, light mapping and normal mapping, and is used in
               games such as Half-Life 2 or Halo 3. This combination allows
               using low-resolution light caching on surfaces with only a
               few coefficients which are evaluated by normal maps to
               render spatial high-frequency changes in the lighting.
               Though there are dedicated bases for this purpose such as
               the Half-Life 2 basis, higher order basis functions such as
               quadratic Spherical Harmonics are needed for an accurate
               representation. However, a full spherical basis is not
               needed since the irradiance is stored on the surface of a
               scene.  In order to represent the irradiance signals
               efficiently, we propose a novel polynomial, hemispherically
               orthonormal basis function set that is specifically designed
               to carry a directional irradiance signal on the hemisphere
               and which makes optimal use of the number of coefficients.
               To compare our results with previous work, we analyze the
               relations and attributes of previously proposed basis
               systems and show that 6 coefficients are sufficient to
               accurately represent an irradiance signal on the hemisphere.
               To create the necessary irradiance signals, we use Spherical
               Harmonics as an intermediate basis due to their fast
               filtering capabilities.",
  month =      feb,
  booktitle =  "Proceedings of the ACM SIGGRAPH Symposium on Interactive 3D
               Graphics and Games 2010",
  isbn =       "978-1-60558-939-8",
  location =   "Washington D.C.",
  publisher =  "ACM",
  pages =      "189--195",
  keywords =   "irradiance, real-time rendering, normal mapping, lightmap",
  URL =        "https://www.cg.tuwien.ac.at/research/publications/2010/Habel-2010-EIN/",
}