Command entry:Main toolbar
(Render Setup)
Render Setup dialog
Choose Default Scanline Renderer as the active production renderer.
Advanced Lighting panel
Select Advanced Lighting rollout
Choose Light Tracer from the drop-down list.
Command entry:Rendering menu
Render Setup
Render Setup dialog
Choose Default Scanline Renderer as the active production renderer.
Advanced Lighting panel
Select Advanced Lighting rollout
Choose Light Tracer from the drop-down list.
The Light Tracer provides soft-edged shadows and color bleeding for brightly-lit scenes such as outdoor scenes. It is typically
used in conjunction with a Skylight. Unlike radiosity, the Light Tracer does not attempt to create a physically accurate model, and can be easier to set up.
TipWhile you can use light tracing for indoor scenes, radiosity is usually the better choice in such cases.
Previewing the Effect of Light Tracing
- To get a quick preview of the effect the Light Tracer will have, lower the values of Rays/Sample and Filter Size.
The result will be a grainy version of the full effect.
- Another way to get a quick preview is to make sure Adaptive Undersampling is turned on. In this group, set the Initial Sample
Spacing sampling and the Subdivide Down To setting to the same value. In the General Settings group, lower the value of Rays/Sample,
and set Bounces equal to 0.0. This gives a rather blotchy but fast preview of the rendering. Increase the Rays/Sample and
Filter Size values to improve the image quality.
In general, you can get good, fairly quick results with a lower Filter Size value as long as Rays/Sample has a high value
and Adaptive Undersampling is on.
Other Tips for Using the Light Tracer
Procedures
To set up a scene for the Light Tracer:
This is a typical use case:
- Create the geometry for an outdoor scene.
- Add a Skylight to illuminate it.
One or more spotlights can also work well. If you use the physically based IES Sun or IES Sky lights, using an exposure control is essential.
- Choose Rendering Advanced Lighting Light Tracer.
This opens the Render Setup dialog to the Advanced Lighting panel and activates Light Tracer.
- Adjust the Light Tracer parameters, activate the viewport to render, and then activate the Common panel.
- Adjust your rendering settings, and then click the Render button at the bottom of the dialog.
The scene renders with soft-edged shadows and color bleeding.
Interface
General Settings group
- Global Multiplier
-
Controls the overall lighting level. Default=1.0.
- Object Multiplier
-
Controls the level of light reflected by objects in the scene. Default=1.0.
NoteThis setting has little effect unless Bounces is greater than or equal to 2.
- Sky Lights [toggle]
-
When on, enables regathering from the Skylights in the scene. (A scene can contain more than one Skylight.) Default=on.
- Sky Lights [amount]
-
Scales the intensity of the Skylights. Default=1.0.
- Color Bleed
-
Controls the strength of color bleeding. Color bleeding results when light is interreflected among scene objects. Default=1.0.
NoteThis setting has little effect unless Bounces is greater than or equal to 2.
- Rays/Sample
-
The number of rays cast per sample (or pixel). Increasing this value increases the smoothness of the effect, at a cost of
render time. Decreasing this value results in a grainier effect, but renders more quickly. Default=250.
TipTo get a “first draft” preview of the effect of light tracing, reduce the value of Rays/Sample and the Filter Size.
- Color Filter
-
Filters all light falling on objects. Set to a color other than white to tint the overall effect. Default=white.
- Filter Size
-
The size, in pixels, of the filter used to reduce noise in the effect. Default=0.5.
TipFilter Size is especially useful when Adaptive Undersampling is turned off, and Rays/Sample has a low value.
- Extra Ambient
-
When set to a color other than black, adds that color as extra ambient light on objects. Default=black.
- Ray Bias
-
Ray Bias, like Shadow Bias , adjusts the positioning of the bounced light effects. Use it to correct rendering artifacts, such as the banding that can
occur when an object casts shadows on itself. Default=0.03.
- Bounces
-
The number of light-ray bounces that are traced. Increasing this value increases the amount of color bleeding. Lower values
give faster results with less accuracy, and typically produce darker images. Higher values allow more light to flow through
the scene, resulting in brighter, more accurate images at a cost of rendering time. Default=0.
When Bounces equals 0, the Light Tracer disregards volumetric lighting.
TipIf your scene has transparent objects such as glass, increase Bounces to be greater than zero. Be aware that this increases
rendering time.
- Cone Angle
-
Controls the angle used for regathering. Reducing this value can result in slightly higher contrast, especially in regions
where lots of small geometry casts shadows on a larger structure. Range=33.0 to 90.0. Default=88.0.
- Volumes [toggle]
-
When on, the Light Tracer regathers light from volumetric lighting effects such as Volume Light and Volume Fog. Default=on.
For volumetric lighting to work with light tracing, Bounces must be greater than 0.
- Volumes [amount]
-
Multiplies the amount of light regathered from volumetric lighting effects. Increase to increase their impact on the rendered
scene, decrease to decrease their effect. Default=1.0.
Adaptive Undersampling group
These controls can help you speed up rendering time. They reduce the number of light samples taken. The ideal settings for
undersampling vary greatly from scene to scene.
Undersampling initially takes samples from a grid superimposed on the pixels of the scene. Where there is enough contrast
between samples, it subdivides that region and takes further samples, down to the minimum area specified by Subdivide Down
To. Lighting for areas not directly sampled is interpolated.
TipIf you use adaptive undersampling, try adjusting the Subdivision Contrast value to obtain the best results. The effect of
this control depends on the value of Rays/Sample.
- Adaptive Undersampling
-
When on, the Light Tracer uses undersampling. When off, it samples every pixel. Turning this off can increase the detail of
the final rendering, but at a cost of rendering time. Default=on.
- Initial Sample Spacing
-
The grid spacing for the initial samples of the image. This is measured in pixels. Default=16x16.
- Subdivision Contrast
-
The contrast threshold that determines when a region should be further subdivided. Increasing this value causes less subdividing
to occur. Too low a value can cause unnecessary subdividing. Default=5.0.
- Subdivide Down To
-
The minimum spacing for a subdivision. Increasing this value can improve render time at a cost of accuracy. Default=1x1.
Depending on the scene geometry, grids larger than 1x1 might still be subdivided below this specified threshold.
- Show Samples
-
When on, sample locations render as red dots. This shows where the most sampling has taken place, which can help you choose
the optimal settings for undersampling. Default=off.