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.

[paper]

- Publication Type: Conference Paper
- Workgroup(s)/Project(s):
- Date: February 2010
- Booktitle: Proceedings of the ACM SIGGRAPH Symposium on Interactive 3D Graphics and Games 2010
- Date (from): 1. March 2010
- Date (to): 21. February 2010
- ISBN: 978-1-60558-939-8
- Lecturer: Ralf Habel
- Location: Washington D.C.
- Pages (from): 189
- Pages (to): 195
- Publisher: ACM
- Keywords: irradiance, real-time rendering, normal mapping, lightmap

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.

@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/", }

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