Global illumination
Global illumination (English Global Illumination, abbreviated GI) referred to in the 3D computer graphics in general the simulation of light interactions of objects. In particular, are meant only those methods that take into account all possibilities of the propagation of light rays in a 3D scene. Thus, the laws of geometrical optics, and energy conservation are fully met and a relatively realistic picture generated.
Method
For the simulation of global illumination are increasingly being used 3D programs, special algorithms that can actually simulate global illumination. These are, for example, path tracing or photon mapping, under certain conditions, radiosity. It always are methods that try to solve the rendering equation.
The following approaches can be distinguished here:
- Inversion: is not applied in practice
- Collection -like approach ( gathering- type): Path Tracing
- Bullet -like approach ( shooting -type ): Light Ray Tracing
- Bidirectional approach: Photon mapping diffuse ray tracing, bidirectional path tracing, Metropolis Light Transport
- Radiosity
In the light path notation global illumination corresponds to the paths of the type L ( D | S) * E.
Image-based lighting
Another way to simulate real global lighting, is the use of High Dynamic Range Images ( HDRI ), also called environment maps which enclose the scene and illuminate them. This process is referred to as image-based lighting.
Faked Global Illumination
Here is " fraudulently " within the 3D software by clever placement of various light sources and by using various tricks GI ( engl. to fake).
In reality, the light particles would be deflected by all objects that reflect or even both.
At the " fake " GI placing the lights so that they act as a substitute for deflected and / or reflected light particles. Usual example, would be a light as a replacement of the primary light source (eg the sun) and other lights that brighten up any extremely dark areas that are not illuminated by the primary light source.
- Image synthesis