Autodesk 12812-051462-9011 User Guide 3 - Page 2835

Photon Map A photon map™ is a technique to generate the indirect illumination effects of caustics on page 6255 and global illumination on page 6261 when you render with the mental ray renderer on page 6230. When it calculates indirect illumination, the mental ray renderer traces photons emitted from a light. The photon is traced through the scene, being reflected or transmitted by objects, until it strikes a diffuse surface. When it strikes a surface, the photon is stored in the photon map. Generating photon maps is time-consuming. To improve performance, you must explicitly specify: ■ Which lights emit photons for indirect illumination. ■ Which objects can generate caustics or global illumination. ■ Which objects can receive caustics or global illumination. The settings for generating and receiving caustics are on the Object Properties dialog > mental ray Panel on page 322. The photon map stores photons only for objects that can receive caustics, global illumination, or both. To further reduce the time required to generate a photon map, photons are limited by the Trace Depth controls. These limit the number of times a photon can be reflected, refracted, or both. In animations, another way to save time is to reuse the photon-map file. If lighting doesn't change over the course of an animation, use the Photon Map controls on page 6312. The mental ray renderer saves photon maps as PMAP files on page 8093. Photon map controls are on the Render Setup Dialog > Indirect Illumination panel > Caustics And Global Illumination rollout on page 6306. PHY Files You can save Physique on page 4603 data to a Physique (PHY) file. This saves data common to all objects that share a given Physique modifier. Later, you can reload the PHY file, either to restore the data that belongs to a particular skin or portion of skin, or to transfer the Physique of one skin (or portion of it) to a different one. 8090 | Glossary