Datasheet

Material Types and Critical Attributes  5
The shared attributes include the following:
Color Color determines its namesake. You can enter specific red, green, and
blue values by clicking the color swatch and updating the Color Chooser
window. For more information on the Color Chooser window, see the
“Adjusting Colors and Transparency” section later in this chapter.
Transparency Much like Color, Transparency uses a color swatch. By
default, Transparency employs a scalar (grayscale) range in which black
is opaque and white is transparent. However, you are free to choose any
color value through the Color Chooser window.
Ambient Color Ambient Color represents diffuse reflections arriving from all other sur-
faces in a scene, as well as reflections from participating media (particles suspended in
air, such as dust, smoke, or water vapor). To simplify the rendering process, the diffuse
reflections are assumed to be arriving from all points in the scene with equal intensities.
In practical terms, ambient color is the color of a surface when it receives no direct light.
A high Ambient Color value will reduce the contrast of an assigned surface.
Incandescence Incandescence creates the illusion that the surface is emitting light. The
color value of the Incandescence attribute is added to the color value of the Color attri-
bute, thus making the material appear brighter. (You can use the Incandescence attribute
to contribute light to a scene when using the mental ray renderer and the Final Gathering
option; this is demonstrated in Chapter 2.)
Bump Mapping At the point of render, bump maps perturb
surface normals along the core of a surface (the central section
facing the camera). They do not, however, affect the surface’s
silhouette edge. For example, in Figure 1.6, a primitive sphere
is assigned to a bump-mapped material. While the core of the
sphere appears craggy, the sphere’s silhouette edge remains per-
fectly smooth. Nevertheless, the bump effect can often sell the
idea that a surface is rough. When the Bump Mapping attribute
is mapped, middle-gray values (0.5, 0.5, 0.5 on a 0 to 1.0 RGB
scale) have no effect. Higher values cause peaks, and lower values
cause valleys to form. For a demonstration of the bump effect, see
the section “Procedurally Mapping Bumps” later in this chapter.
Diffuse The term diffuse refers to that which is widely spread
and not concentrated. Hence, a real-world diffuse surface
appears matte-like and does not create highlights or specular “hot spots.” This is because
of the presence of myriad surface imperfections that scatter light in a random fashion.
For example, paper and cardboard are diffuse surfaces. In Maya, the Diffuse attribute
controls the degree to which light rays are reflected in all directions. A high Diffuse
Figure 1.5
Attributes shared
by Lambert, Blinn,
Phong, Phong E,
and Anisotropic
materials
Figure 1.6
A bump-mapped
sphere renders with
a craggy core and a
smooth silhouette
edge.
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