Photon Mapping

Photon mapping is one of Henrik Jensen When published in 1995 the image synthesis algorithm, which is used primarily as an extension of ray tracing - based methods. The goal of photon mapping is to determine the global illumination of a scene efficiently and thus to generate realistic images in less time. Photon mapping is one of the Particle tracing methods.

Method

In photon mapping are before the actual rendering process called " photons" that carry a certain power ( radiant flux ), "shot" of the light sources in the scene. Geometrically, this corresponds to the ray tracing from the light source starting. A photon is significantly abstracted by its position, the direction from which it is irradiated, and their radiant flux. Meets such of the light source emitted photon has a surface, it may be reflected, scattered, refracted, absorbed or stored in the photon map, when it encounters a diffuse reflective surfaces. It may be the performance of the photon is changed. The photon map ( rare: " photon map " ) is independent of the scene geometry data structure (usually a three-dimensional kd - tree). The data stored in their photons can give an estimate of the depth at the position of the photon radiation flux. The entire process is called photon tracing.

The term " photon " as used true only to the extent consistent with the physical concept, is transported as radiant flux. This is not the photon mapping to a quantum- physically correct simulation of light propagation. Instead, abstracts a " photon" in photon mapping a large number of physical photons whose energy is accumulated to the power of " photon " per unit of time. Quantum physical processes are not taken into account, since to produce realistic -looking images, the geometrical optics is usually sufficient.

The photon thus created map can be used in different ways. It is common practice, the method in which the rendering of each point at which a beam incident on a ray tracing during the surface indirect illumination is determined by the density and performance of the photons in the photon map in the vicinity of each point. By adding the thus determined indirect lighting and diffuse determined by ray tracing direct lighting can calculate global illumination of a scene. In addition, the photon map can be used to accelerate path tracing. For efficient simulation of caustics they are stored in an independent Caustic Map.

The difference to other of the light source operating procedures such as Light ray tracing or previous Particle -tracing methods is that the indirect lighting is determined only once in a single operation and stored independently of the geometry.

For photon mapping, there are other applications and extensions as Importon mapping and volume scattering.

Support

Photon mapping is now supported by most major renderers. The most common renderer is mental ray, which is a standard feature in many major 3D software packages. Other renderers like POV -Ray, YafaRay, V -Ray, Maxwell Render and LuxRender support photon mapping.