3ds Max 2012 Bible - Kelly L. Murdock [471]
Radiosity computes lighting solutions that are much more realistic than using standard lights. As you learn to use radiosity, you quickly discover that it is a complex system that takes lots of tweaking to get just right.
Selecting Advanced Lighting
You control the advanced lighting settings for the scene in the Advanced Lighting panel, which is part of the Render Scene dialog box. You can access this panel by selecting Rendering⇒Light Tracer or Rendering⇒Radiosity (or by pressing the 9 key). The Advanced Lighting panel includes a rollout with a single drop-down list where you can select the lighting plug-in to use. The options are None, Light Tracer, and Radiosity.
Note
The Light Tracer and Radiosity options aren't available if the mental ray renderer is enabled. •
Light Tracer and Radiosity are two different techniques for applying advanced lighting to a scene. Although they are fundamentally different, they both simulate a critical piece of the lighting puzzle that adds dramatically to the realism of the lights in the scene—light bouncing. When light strikes a surface in real life, a portion of the light bounces off the surface and illuminates other surfaces. Traditionally, Max hasn't worried about this, which required that users add more lights to the scene to account for this additional lighting. Both the Light Tracer and the Radiosity solutions include light bouncing in their calculations.
How light tracing works
The Light Tracer is a Global Illumination (GI) system that is similar to raytracing, but it focuses more on calculating how light bounces off surfaces in the scene. The results are fairly realistic without being computationally expensive, and its solutions are rendered much quicker than a radiosity solution.
Cross-Reference
The Light Tracer is similar in many ways to raytracing. Chapter 47, “Rendering with mental ray and iray,” presents more information on raytracing. •
The Light Tracer works by dividing the scene into sample points. These sample points are more heavily concentrated along the edges of objects in the scene. An imaginary light ray is then shot at each sample point, and the light intensity at the location of contact is recorded; then it is computed where the light ray would bounce to, and a reduced intensity value is recorded. One of the settings is how many times the light rays will bounce within the scene, and this value increases the amount of time required to compute the solution. When all the rays and light bounces have been computed, the total light intensity value for each sample point is totaled and averaged.
Caution
Transparent objects split each ray in two. One ray bounces, and the second ray is projected through the transparent object. Transparent objects in the scene quickly double the amount of time required to compute a solution. •
The end result of a light tracing solution is that objects that are typically hidden in the shadows become much easier to see. Figure 45.1 shows a house model that was rendered using the standard lighting solution with raytraced shadows and then again using the Light Tracer opened side by side in the RAM Player. Notice that many of the details hidden in the shadows of one figure are visible in the other.
FIGURE 45.1
A house scene rendered using standard lighting (left) and light tracing (right)
Enabling light tracing
To enable light tracing in a scene, select Rendering⇒Light Tracer to open the Advanced Lighting panel in the Render Scene dialog box, as shown in Figure 45.2.
FIGURE 45.2
The Light Tracer Parameters rollout sets values for GI lighting.
The Global Multiplier value increases the overall effect of the Light Tracer, much like increasing the multiplier of a light. The net result is to brighten the scene. You also can increase the multiplier of