STEP 1: Apply the ambient occlusion node by itself
The ambient occlusion node is quite scale-dependent, so begin by applying it by itself to make sure you get the effect you want. In the Surface Editor, select the desired surface. Make sure that it has some kind of non-black color, then turn Diffuse to 0%. Ensure that the checkbox for nodal surfaces is on, then click Edit Nodes. In the popup box, select Shaders > Diffuse > Occlusion. The Occlusion node will appear. Connect the output of the Occlusion node into the surface’s Luminosity. Render a frame. You’ll see that the Occlusion node gives a nice representation of where the small details are. The darker areas are tighter, and these are the areas that are more prone to looking CG if the reflection is overly bright.
STEP 2: Darken your shadows without blackening them
Double-click the Occlusion node to bring up the interface. By default, the Occlusion node’s mode is set to Infinite, which means rays will trace out from the surface to infinity. But you’ll want the occlusion to be a bit tighter- you want to darken, not blacken, the metal. Set the mode to Ranged and the range to 100mm. Check the results with a test render. You’ll see that the image is overall a bit brighter, as the darkened areas have retreated.
STEP 3: Set parameters for the surface
Now, disconnect the Occlusion node from the Luminosity. You’ll need to set up some parameters for a basic chrome surface. It’s easy to do the whole thing with nodes. Add a Constant > Scalar node, set it to .2, then connect it to Diffuse. Copy and paste the Scalar node, set it to.9, then connect it to both Specular and Glossiness. This will give the metal tight, shiny highlights.
STEP 4: Continue tweaking reflections
Add a Gradient node, and double-click it to bring up the interface. Set the Input to Incidence, then set the first key’s color to pure white. Add another key at 1, and set it to RGB 200,200,200. This will give some Fresnel variation in the reflectivity of the chrome, but still leave it very shiny. Connect the output color of the gradient into Reflection. Make sure you have some image or gradient in the background to reflect and have turned Trace Reflection on; then do a test render.
STEP 5: Link your nodes and render!
Now all you need to do is combine the reflection gradient with the occlusion, which you can do with a Multiply node. Go to Add Node > Math > Scalar > Multiply. Connect the output of the Occlusion node to the A input, and the Gradient‘s color output to the B node– don’t worry about connecting a color-type node to a scalar node. Since we don’t actually have any color in it, we won’t be losing any information. Then render. You can see now how the small interior details of the engine are less reflective, therefore darker, giving much more depth and contrast to the scene.
Lead CG Artist
Jarrod Davis began his VFX career at Foundation Imaging, working on Roughnecks: The Starship Troopers Chronicles. He also worked on the Emmy-award-winning series finale of Star Trek: Voyager and the Emmy-award-winning pilot of Enterprise. In 2002 he joined forces with some of his old Foundation colleagues to work on Firefly, which won them all their own Emmys and became the flagship show for the newly formed Zoic Studios. There, Jarrod and the Zoic crew have worked on groundbreaking television shows such as CSI, Battlestar Galactica and Drive, as well as commercials, games and films, including Serenity and Talladega Nights: The Legend of Ricky Bobby.
You can learn more about LightWave 9.0’s new features in Jarrod’s training DVD, "What’s New in LightWave 9.0," available from Class on Demand (www.classondemand.net).
Jarrod Says Keep in Mind…
Graphic artists are always looking for ways to take the edge off that "CG" look. One of the most difficult things to do well in CG is create shiny, polished metal surfaces, like chrome. Reflective surfaces in CG tend to over-light themselves, and the result can scream like a preschooler wanting attention. A great way to solve this problem is to use LightWave 9.2’s Ambient Occlusion node in a slightly unconventional way. This technique will work well for any chrome surfaces, but it’s especially nice with more complex geometry that has lots of nooks and crannies, like the featured CG Harley Road King engine.
After you complete the tutorial, try experimenting with nodes. Don’t limit yourself to using them the way you think they should be used. Their completely open nature means you can connect things in some surprising and useful ways.
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