3D Animation for the Raw Beginner Using Maya

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 don’t 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.