Shot lighting in Renderman
Discover top lighting techniques with this expert advice from Renderman specialist Leif Pedersen
Leif Pedersen showcases Renderman’s top lighting capabilities for effective storytelling in animation
Leif is a Renderman specialist at Pixar’s Renderman team, where he loves to showcase some of the most artistic and technical aspects of the renderer. leif3d.com
In this training we’ll use a scene from Pixar co-op short film, Only a Dream, where we’ll learn to use some of the most effective Renderman shot lighting tools. During this process, we’ll understand how to make meaningful artistic choices in order to tell the best story possible, while digging into some of the more technical aspects of mastering shot lighting in Renderman for Maya.
Our main goal as lighting artists is to tell a story, in this case, a coming-of-age thriller. The aesthetic we’re going for is film noir with an analogous blue/ green colour palette. In fact, one of the colour inspirations was the Chernabog Demon sequence from Disney’s Fantasia. In order to achieve our look, we’ll mix a couple of different lighting techniques, including low-key and motivated lighting, which will give the scene a bit of drama while heavily art directing the shot to create the look we need.
01 MASTER LIGHTING
A useful way to start is through an environment light. We’ll use a Pxrdomelight with an industrial HDRI map which is full of small and bright lighting features, yet offers dim diffuse lighting. This will give us interesting glints to bring out shiny surfaces. If light is overpowering, Renderman offers decoupling of diffuse and specular under the Refine tab in all lights. Using light temperature is also a great way to stay within a plausible aesthetic, as it’s based on physical Kelvin colour temperatures, but don’t be afraid to add or remove colour for a more stylised look.
02 DIRECT YOUR SCENE
Lighting direction is crucial for the mood of the shot, and by using low-key lighting we can start to produce a scarier mood. To achieve this, we are pointing lights from the floor to the ceiling to bring a gradient of light intensity in our room. Rect and Disk lights work well for this but their direction might be too obvious, so adding Sphere lights is useful when we want to cover a larger area or soften shadows. If you’re looking for further realism, try using IES profiles which will create photometric light patterns common in light bulbs.
03 SHOT LIGHTING BLOCKING
The Chernabog Demon sequence uses complementary colours to its blue palette to highlight key moments in the storytelling, such as oranges and yellows. We’re doing the same with our key light in order to bring out the warm tones in our character’s face. The key light is coming from the bottom left, in order to create that low-key aesthetic we’re aiming for. We’ve also added a bounce light in an opposing direction to shape our character’s face. It’s sometimes useful to normalise our lights to avoid intensity changes while scaling the lights during our blocking stage.
Lighting is a storytelling tool, so it’s always good to bring out the character in a shot so that it doesn’t get lost in the frame, as
this helps the viewer to focus on what’s important. To do this, we’re creating kicker lights to highlight the hair specularity and rim lights to make our character pop from the background. Our kicker light for the hair specularity is giving us unintended highlights in both the eyes and face; to control this, we are removing the contribution of this light via Maya’s Relationship Editor>light Linking.
05 LIGHT FOR ANIMATION
It’s very important not to rely on a single frame for lighting and always check the animation sequence for context. In our shot, the character starts out in penumbra, guiding the viewer to the item in her hand. As the shot then progresses, we shift focus to the character’s face and her reaction to that element in the story. To do this, we are animating the light intensity of our low-key bounce light to direct the viewer, as well as decreasing the specularity of that light by 80 per cent so that it doesn’t overwhelm the eyes with reflections.
06 BLOCK AND ISOLATE LIGHTS
The current setup is going in the right direction, but it’s looking flat, so we need to shape it further. The most common way to manipulate lights is through light filters, which provide a non-destructive way to block, isolate or colour lights, even portals! We’re using Pxrrod and Pxrblocker light filters in this scene in order to shape a film-noir aesthetic in our character’s face. We can simply right-click on our light filter attribute and pick from a list of available options. Using the same tools, we’ll refine and shape our environment as well.
07 LIGHT GROUPS
Besides AOVS and LPES, Renderman can output arbitrary light groups by simply assigning a light group name to the light under Advanced>light Group. We can then go to our Render Settings>aovs tab and create a new channel to display our light group, such as a new beauty pass.
Don’t forget to check Adapt All under Render Settings>
Advanced, so that your new passes are not noisy.
This comes in handy for compositing, or troubleshooting, so that you can isolate a single or group of lights with any arbitrary lobe, and you can now do this interactively too!
08 LIGHT PORTALS
Due to the sampling principles in path tracing, interior lighting is usually less efficient than exterior lighting, because camera rays have a harder time finding light sources when they are hidden from the camera – as in the example of our dome light, which is being covered by the house. To make this more efficient, Renderman can use portal lights, which communicate to the renderer where the lighting is coming from. We’re using one portal light for each window or door opening, which can have a dramatic effect on sampling quality, converging renders faster.
09 RENDER EFFICIENTLY
We’re taking advantage of Pxrunified, Pixar’s own studio integrator, which has sophisticated ray termination and light learning technology. This will allow us to have higher trace depths for our final frames, improving the look of our hair and skin. We also have the Denoise button checked on in our AOVS Display tab, which will enable us to use the Nvidia Optix denoiser in the IT viewer by pressing ‘N’ (not available on OS X) and will also take care of the denoise process automatically for batch rendering.
If your computer is struggling with resources, try switching resolutions or adjusting sampling settings interactively. •