Autodesk 12812-051462-9011 User Guide 3 - Page 915

Computer Graphics Rendering The 3D models created in 3ds Max contain geometric data defined in relationship to a 3D Cartesian coordinate system, referred to as world space on page 8175. The model also contains other information about the material of each of the objects and the lighting in the scene. The image on a computer monitor is made up of many illuminated dots, called pixels on page 8092. The task in creating a computer graphics image of a geometric model is to determine the color for each pixel based on the model information and a specific viewpoint (camera). The color of any specific point on a surface in a model is a function of the physical material properties of that surface and the light that illuminates it. Two general shading algorithms: local illumination and global illumination are used to describe how surfaces reflect and transmit light. Local Illumination Local illumination algorithms describe only how individual surfaces reflect or transmit light. Given a description of light arriving at a surface, these mathematical algorithms, called shaders in 3ds Max, predict the intensity, color, and distribution of the light leaving that surface. In conjunction with a material description, different shaders will determine, for example, if a surface will appear like plastic or metal or if it will appear smooth or rough. 3ds Max provides a robust interface for defining a wide array of different surface materials. After defining how an individual surface interacts with light at the local level, the next task is to determine where the light arriving at the surface originates. With the standard scanline rendering system on page 8116 of 3ds Max, only the light coming directly from the light sources themselves is considered in the shading. For more accurate images, however, it is important to take into account not only the light sources, but also how all the surfaces and objects in the environment interact with the light. For example, some surfaces block light, casting shadows on other surfaces; some surfaces are shiny, in which case we see in them the reflections of other surfaces; some surfaces are transparent, in which case we see other surfaces through them; and some surfaces reflect light onto other surfaces. Global Illumination Rendering algorithms that take into account the ways in which light is transferred between surfaces in the model are called global illumination 6170 | Chapter 20 Rendering