2008

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
■ To improve rendering time, use the
Object Properties dialog on page 245
to disable light tracing (or radiosity solving) for objects that don't have a
great impact on the final effect.
TIP You can also use the Advanced Lighting Override material on page 5572
to alter the effect of light tracing on particular objects. For example, if you
encounter visual artefacts with a bump-mapped material, convert it to an
Advanced Lighting Override material and reduce the Indirect Light Bump Scale
value.
■ Experiment with the Adaptive Undersampling group settings, which restrict
light tracing to the areas of your scene that need it.
■ To increase the amount of color bleeding, increase the values of both
Bounces and Color Bleed. Color bleeding is usually a subtle effect.
■ If there are glass objects in the scene, increase the Bounces value to an
amount greater than 0. But be aware that this increases rendering time.
■ If the main scene lighting is a
Skylight on page 4940 , and you need specular
highlights in your scene, add a second light: for example, a Directional
light that parallels the Skylight. Make sure Shadows are turned on for this
light, and on the light's
Advanced Effects rollout on page 5055 , turn off
Diffuse.
If the objects with highlights don't greatly affect shadows or color bleeding,
you can leave Diffuse on for this light, and use Object Properties to exclude
the objects from light tracing.
■ Set Key filters are not taken into account when you animate Light Tracer
settings. If you wish to use Set Key to create keys for animating the Light
Tracer parameters, Shift+right-click the spinner to create those keys.
IMPORTANT If you use a texture map with the Skylight, you should use an
image-processing program to thoroughly blur the map before using it. This
helps reduce variance and the number of rays needed for light tracing. You
can blur the map beyond recognition, and it will still look correct when used
for regathering.
5966 | Chapter 18 Rendering