Autodesk 12812-051462-9011 User Guide 3 - Page 1042

because each final gather averages over many values of indirect illumination, lower accuracy is sufficient. In film production work, final gathering increasingly replaces photon mapping, except for caustics. Without multiple-bounce effects, which are performed by photons by default and by final gathering only if the shaders adjusts the trace depth, tends to have far less impact on the final image than the first bounce that final gathering supports by default. Although physical correctness is lost, this is often sufficient for film production, and final gathering is easier to control than photons emanating from distant light sources. However, for accurate indoor illumination simulations and other CAD-related applications, photon mapping is still the method of choice. Procedures To use an environment map as a final gather light source: Illumination from which final gathering is derived can be provided by an actual light source, of course, but it can also be provided by an object to which a self-illuminated material is applied, or even an environment map. In the latter case, follow this procedure: 1 Add a skylight on page 5065 to the scene. 2 Do either of the following: ■ On the Skylight Parameters rollout, make sure Sky Color (the default) is chosen, click the map button ("None") to open the Material/Map Browser dialog and then choose a map. ■ On the Skylight Parameters rollout, choose Use Scene Environment. Use the Environment panel on page 6689 controls to assign an environment map. Thereafter, rendering with final gather enabled take the skylight map into account when calculating final gather illumination. TIP For extra realism, use an HDR image on page 7334 as a Bitmap map image on page 5795. mental ray Renderer | 6297