371
Chapter 15
Advanced Light and Materials
Properties and Effects
I
    look at some advanced topics involving light and materials.
AMBIENT OCCLUSION
Ambient occlusion refers to the ability to control the spread of ambient light. In English, to
occlude something is to block it. So, by controlling ambient occlusion we can increase or
decrease the spread of ambient light. If we block it more, small areas in a render will turn
dark. If we let ambient light spread, we will wash out areas that otherwise might have been
in shadow.
Ambient occlusion in Maya is used to keep ambient (widely dispersed) light from wash-
ing out small areas. We might use ambient occlusion to add shadows to small areas in order
to draw out the small-grained relief on the surface of a model.
Figure 15.1 contains two copies of the Mudbox default horse. ey have a reective
mia_material on them, as seen in Figure 15.2. A background plane with a light Blinn on it
has been added. ere are three lights in the scene, two ambient lights and a spotlight; see
Figure 15.3. Note that we have not checked o the Use Ambient Occlusion option in the
attribute box of the material; see Figure 15.4. See the render in Figure15.5, or, for a better
view of the horse renderings, see the color gures on: http://3DbyBuzz.com.
Now, we want to start controlling the eects of ambient light. ere is a group of
attributes of the mental ray mia_material that we can set by checking the Use Ambient
Occlusion box.
In Figure 15.6, we have checked this box. We are going to focus on two attributes as we
strive to gain control of ambient light. First, we change the color of the light to white, as
seen in Figure 15.6. e result is seen in the render in Figure 15.7.
372 3D Animation for the Raw Beginner Using Maya
FIGURE 15.1 Horses.
FIGURE 15.2 Mia_material blue.
Advanced Light and Materials Properties and Effects 373
FIGURE 15.3 Two ambient lights and a spotlight.
FIGURE 15.4 Ambient occlusion not checked.
374 3D Animation for the Raw Beginner Using Maya
FIGURE 15.5 Default render of horses.
FIGURE 15.6 Ambient occlusion and white light.
Advanced Light and Materials Properties and Effects 375
Now, in Figure 15.8, we have changed the light color to a gray. We get the render seen
in Figure 15.9. is is a better balance, as we can now more easily see the variations in the
color of the horses; they have a deeper 3D appearance.
en we change the Distance to 100 and get the render in Figure 15.10. is is probably
the best render yet, as it draws out the more shadowed parts of the horses while maintain-
ing the overall contrast.
So, what have we done?
First, we probably want a gray light, so we dont get a stark, washed out look.
What about the Distance attribute? It controls how far the eects of ambient occlusion
spread from a given point. A larger number makes things darker and a smaller number
makes them brighter. Why? Because as we increase the Distance, we are increasing the
distance over which we limit the movement of ambient light.
Just to point out the importance of choosing a color for the light in the scene, in Figure
15.11, we have replaced the Ambient Light Color by clicking on the small checkerboard at
the right of the slider and then choosing the checkerboard texture in the Hypershade. So,
parts of the ambient light have been turned to black, while others are as bright as the horses
in Figure 15.7.
GLOBAL ILLUMINATION AND FINAL GATHERING
We have looked at depth map versus raytraced shadows as well. We will review Global
Illumination and Global Illumination and Final Gathering and then introduce a couple of
new things: Caustics and Irradiance. Our goal is to consider a few dierent ways of adding
light eects to a scene. We will be using the mental ray renderer.
As a reminder, Final Gathering, which is an option you can set in the mental ray ren-
derer, adds some extra computations to the raytracer, and in doing so, lls in small dark
FIGURE 15.7 Render of AO and white light.

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