Autodesk 12812-051462-9011 User Guide 3 - Page 328

Max such plug-ins are known as exposure controls and are accessed from the Environment dialog. Use Final Gathering and Global Illumination The Arch & Design material is designed to be used in a realistic lighting environment; one that incorporates full direct and indirect illumination. mental ray provides two basic methods for generating indirect light: Final Gathering and Global Illumination. For best results, be sure to use at least one of these methods. At the very least, enable Final Gathering, or use Final Gathering combined with Global Illumination (photons) for quality results. Performance tips for using Final Gather and Global Illumination can be found here on page 5593. If you use an environment for your reflections, make sure the same environment (or a blurred copy of it) is used to light the scene through Final Gathering. In 3ds Max this means you should include a Skylight on page 5065 in your scene set to Use Scene Environment, or use Daylight system on page 5139 with Skylight set to mr Sky. Use Physically Correct Lights Traditional computer-graphics light sources live in a cartoon universe where the intensity of the light doesn't change with the distance. The real world doesn't agree with that simplification. Light decays when leaving a light source due to the fact that light rays diverge from their source and the intensity of the light changes over distance. This decay of a point light source is 1/d2; in other words, light intensity is proportional to the inverse of the square of the distance to the source. One of the reasons for this traditional oversimplification is the fact that in the early days of computer graphics, tone mapping was not used and problems of colors blowing out to white in the most undesirable ways was rampant. (Raw clipping in sRGB color space is displeasing to the eye, especially if one color channel clips earlier than the others. Tone mapping generally solves this by "soft clipping" in a more suitable color space than sRGB.) However, as long as only Final Gathering (FG) is used as indirect illumination method, such traditional simplifications still work. Even light sources with no decay still create reasonable renderings. This is because FG is concerned only with the transport of light from one surface to the next, not with the transport of light from the light source to the surface. mental ray Materials | 5583