Global Illumination algorithms calculate and reproduce the effects of light as it behaves in the physical world by computing secondary bounces of indirect light within a scene. In this way, GI can produce compelling, photo-realistic results. The price of this realism, however, is rendering time. Depending on deadlines, GI can be an impractical luxury, so other approaches to lighting must be explored. Many production environments typically render separate passes for each light without GI. They are composited to build the lighting, which can then be adjusted in real time.
This article discusses the Scanline rendering engine within 3ds Max. Although Max has long embraced Mental Ray, Scanline is still with us. The techniques discussed here can apply to any renderer with GI turned off. Scanline calculates direct light so surfaces can not contribute reflected light to a scene. To light a scene in a realistic way requires additional lighting to simulate the subtle effects of bounced light.
Fig. 1: Direct light only
Fig. 2: Direct light with fill lighting step 1
Fig. 3: Direct light with fill lighting step 2
GI Lighting model
Make a quick GI render of your simplified scene. Use this as a reference as you build the lighting in Scanline. With interiors, typically the walls & ceilings account for the majority of illumination.
Fig. 4: Interior GI light model
The Elliptical Gradient
Because our eye sees in perspective, real-world illumination is asymmetrical and creates a non-uniform gradient pattern, however slight. This elliptical pattern is what convincingly delineates 3D space. The angle and direction of these gradients together create the visual rhythm that makes up the world as we perceive it.
Linear or radial gradients on surfaces look synthetic; these shapes are not found in nature and disagree with the visual vocabulary built by our experiences. The brain expects to see the world with specific subtleties of light and shadow. We know intuitively when something looks “right”, or when it is does not.
Fig. 5: Elliptical Gradient, high contrast
Fig. 6: Elliptical Gradient
“Scene Lights” are obvious in the scene. Their source is sometimes visible, but always implied. These include, the sun, windows, light fixtures, etc. Begin with the shadow map type, for fastest render feedback. Target spots make good scene lights since they are easy to manipulate. The Sun should be a target direct. Light placement and control of far attenuation are essential to achieving elliptical gradient illumination.
“Fill Lights” represent bounced light and illuminate spaces that would be left in shadow with direct lighting alone. A window may need a light to represent light’s initial spill onto the floor.
Skylights help bring out ambient lighting while providing subtle shadows. Turn shadows on with a low sample count, 5 – 10. Skylights are the biggest render hit in Scanline, so save the higher samples for the final.
Omni Lights can be shaped using the Non-Uniform Scale tool to affect the Far Attenuation sphere. Squash it to conform to the space the light is affecting. When positioning lights avoid hot spots and uncheck “Affect Specular”. Exclude an overly lit surface from a light and create a fill light to independently control that area. When adjusting color look to nearby objects and materials.
Fills first – Begin with Fill Lights to individually light the walls, floor & ceiling. Position spots opposite a wall and set them to include objects along it. Avoid shadows at first. Set cone to rectangular and adjust the Hotspot & Falloff to fade at the edges. Adjust the light’s rotation to work in conjunction with the Far Attenuation field to shape the way light is spread on the surface. Add Omnis to fill out the scene. Add Scene Lights as accents.
Scene Lights first – Begin with Scene Lights, and add Fills as needed.
This approach works well for more complex spaces, or when there is a lighting plan to follow. IES lights are useful for their color and throw pattern but are not as easy to control as standards.
Scanline Global controls – Environment, Global Lighting, & Exposure
Tint Level and Ambient Color influence scene lighting rather than environment color. Exposure can be left off. Though helpful in normalizing the tone in an image, exposure can clamp bright materials and limit an individual light’s intensity.
Ambient Occlusion Pass – the finishing touch
An AO pass is a separate rendered image that contains details of the geometry. Areas where faces converge at an angle are rendered darkest, producing a grey scale image that conveys the solidity of the geometry. The AO image is layered over the diffuse image using the multiply channel in a paint program.
This lighting overview is meant to extend the digital artist’s perception, skill set, and ability to create successful imagery on deadline.
Fig. 7: Ambient Occlusion pass
Fig. 8 Vray – render time 1.5 hours at 2400 x 1600 px
Fig. 9: Scanline – render time 12 minutes at 2400 x 1600 px
Tom Cipolla is a digital artist specializing in architectural visualization. Born in New York, he trained as a sculptor and transitioned to working digitally in 2000. Tom has taught foundry practice, sculpture, drawing and 3D software. His company, Onion3d, is a consulting and animation studio located in South Boston, MA.