Irradiance Environment Mapping

The term Irradiance Environment Mapping encompasses all environment mapping methods for transmitting light to objects. Environment mapping is traditionally used to represent spatially independent, spherical functions, for example to represent reflections on a reflective object. However, diffuse light transmission can also be simulated. In this way, the light transfer can be precalculated for complex illuminated objects.

Calculation of irradiance maps

The diffuse luminance at a point in space with a normal vector can be viewed as the sum of all light sources , weighted with the ambient color , that radiate from the direction . With the help of Lambert's law of cosines this results ${\displaystyle B}$ ${\displaystyle \mathbf {n} }$ ${\displaystyle c}$ ${\displaystyle l_{i}}$ ${\displaystyle \omega _{i}}$

${\displaystyle B=c\sum _{i}\max(0,\mathbf {\omega _{i}} \cdot \mathbf {n} )\cdot l_{i}}$

This ratio can be derived from a 180 ° recording, e.g. B. a sphere map, by considering each pixel of the texture as a separate light source. The result can in turn be saved in a texture and simply transferred to the object at runtime.

Depending on the lighting model used, so-called diffuse irradiance maps or specular irradiance maps are created . A faster calculation and use at runtime is achieved by using spherical surface functions .

Literature and further sources

1. ↑ Ramamoorthi et al .: An Efficient Representation for Irradiance Environment Maps , In: Proceedings of ACM SIGGRAPH 2001, pp. 497-500
2. ^ Gary King: Real-Time Computation of Dynamic Irradiance Environment Maps , In: GPU Gems 2