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Under the Hood

Experimenting with Volume Displacement techniques with the Arnold renderer in Maya

By Lee Griggs

The Arnold renderer has been used by the biggest names in the VFX and animation worlds, and in movies from Gravity to Guardians of the Galaxy Vol. 2. Arnold gives you an easy way to render scenes using real world and on-set lighting techniques, allowing you to focus on the art side of your creations rather than managing software functionality.

I’ve personally used Arnold for years in my own design creations to get photo-real, hyper-real and surreal abstract effects. When working through my own designs, photography and traditional art are my main inspirations. Sites such as Pinterest are a good source of inspiration. Time away from the computer is equally important. Meditation, a walk in the park, or even a quiet coffee somewhere can also be good for generating ideas. 

Standard Volume Shader

I recently started to experiment with a new technique using the Standard Volume Shader, which is a new feature available in Arnold 5 and is often used with VDB volumes. The typical use case for this shader is for more traditional effects like smoke, fire, and clouds. But as I started experimenting with what it could do, I found a more unusual and different way to create a visually interesting, detailed, and unique look that was unlike anything I’d worked on before. I’m calling the technique Volume Displacement.

I want to let other artists know about Volume Displacement and have an opportunity to experiment with its many creative uses, which even I am only just beginning to explore. And, you can use it in all of the supported 3D DCC tools including Maya, 3ds Max, Cinema4D, Houdini and Katana.

I’d like to walk you through how I created this image using the Volume Displacement technique; with Maya and Arnold.

The image started as a VDB file that I had previously created. I started by cranking the density until the image looked like geometry. The effect gives the volume an abstract yet realistic look.

Camera Projection and Depth of Field

I really wanted to make the texture pop, so I projected an organic-looking texture map through the camera, using a Camera Projection node. I have a library of texture maps that keeps growing, and organic texture sources are some of my favorites as they help break out of traditional CG looks. I tried other projection types as well, but they didn’t give me the level of detailing that I was going for.

I then added Depth of Field to hide some of the projection effect—which initially looked a bit strange but I kept experimenting until I had something I liked. For me, it’s all about experimentation with different textures and projections. My advice is to try them all. It’s trial and error and oftentimes they won’t work, but it can be quite the payoff when they do. The result here, I think, is a kind of undersea quality.

Range Shader

I really like how I was able to get the wispy tendrils to fade off. I used a Range Shader to remap the input values of the original texture to displace the volume shading effect, which added contrast and created the gaps and holes in the volume. The Range Shader can often come in handy for manipulating textures to get different and unexpected results. The final image used an Output Max value of 4. It just gave it more of a solid object feeling—almost like coral.

Scatter and Transparent Colors

I tried to connect the displacement texture to the color, but I couldn’t get the look I wanted. Instead, I used the Scatter and Transparent Colors settings in the Standard Volume Shader to control the colors. Scatter is the brightness of the volume under illumination. Its the ratio of light that is scattered rather than absorbed. Again, it’s all about using experimentation to get the desired effect.

In terms of lighting, I wanted to give the image some backlighting that would show through the edges. I added a single HDRI light source in the background and adjusted the Transparent Color setting to let the light bleed through.

Without Depth of Field

Volume Ray Depth

Volume Ray Depth allows you to configure settings that limit the ray recursion based on ray type, and can help you create dramatic differences to a scene or image. Increasing the Volume Ray Depth allowed me to add multiple scattering bounces within the volume. This gave me the desired length, but increased render times. Fortunately, the test rendering in the interactive Arnold RenderView is remarkably fast, and I was able to move the process along fairly quickly. Overall, it was worth it, as the volumes look so much more believable, and the fact that I could get closer to the final result saved a lot of time downstream during compositing and creative finishing. I would recommend keeping volume shading networks as lean as possible. This is important for render times in the volume context because the network is evaluated so often.

Get under the hood

As you probably know by now, I’m a huge fan of experimentation—especially when it comes to what I can do with the Arnold renderer. While I’m most comfortable working in Maya, the Volume Displacement technique can be used in the other Arnold supported applications as well.

To try the Volume Displacement technique, all you need is the current version of Maya and my free Volume Shader file. If you already subscribe to Maya, you’re all set. If you want to try Maya for free, click here.