Basic Surface Properties
When an image is rendered many factors influence how the surface of an object is displayed. These factors determine, for example, if only the brightness and color of a surface will be calculated or if the surface is reflective or transparent.
The brightness of a given point, which is based merely on the angle of the light hitting it, is generally calculated very quickly. However, since almost no surface is perfectly smooth, a certain degree of light dispersion will always take place. The rougher a surface is, the less reflective and transparent it is and the larger the specular highlight is. In fact, specular lighting is one of the most important surface properties. This property alone conveys to the viewer how rough or smooth the surface is. In the image below, the difference between the two materials, each with different specular highlight settings, can be readily seen.
The brightness falloff on the curved surface is also an important element. This can be influenced by shadow types. Shadow types define the proportional relationship between the shaded and specularity lit areas of a surface. As a rule you can assume that a polished surface will have a smaller, more intense specular highlight and this intensity will quickly subside on the surface’s shaded areas (i.e. the surface adjacent to the point at which the light hits the surface). This is due to the fact that a smoother surface creates less dispersion of light.
A rough surface on the other hand will have a more dispersed shading over which a broad, weak specular highlight will lie. The image below shows two very different shadow types for comparison:
Most of the remaining material parameters are used to more-or-less mix color values for the surface color. For example, the Luminance channel can be used to add colors independent of the illumination of the surface.
The object’s environment can influence the surface of an object by applying Transparency or Reflection channels. The following sections will expound on these and other material channels.