8

Light Tracer 45
Other Tips for Using the Light Tracer
• To improve rendering time, use the Object
Properties dialog (page 1–111)
to disable light
tracing (or radiosity solving) for those objects
thatdon’thaveagreatimpactonthefinaleffect.
Tip: You can also use the Advanced Lighting
Override material (p age 2–1410)
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
settings, which restric t light tracing to the areas
of your scene that need it.
• To increase the amount of color bleeding,
increase the value of both Bounces and Color
Bleed. Color bleeding is usually a subtle effect.
• If there are glass objects in the scene, increase
Bounces to be greater than zero. (Be aware that
this will inc rease rendering time.)
• If the main scene lighting is a
Skylight (page
2–1149)
, and you need specular highlights in
your scene, add a second light: for example,
a Direct ional light that parallels the Skylight.
Make sure Shadows are turned on for this light,
and on the light’s
Advanced Effects rollout
(page 2–1185)
, tur n off Diffuse.
If the objects with highlights don’t greatly
affect shadows or color bleeding, you can
leaveDiffuseonforthislight,anduseObject
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
touseSetKeytocreatekeysforanimatingthe
Light Tracer parameters, SHIFT+right-click
the spinner to create those keys.
Impor tant: If you use a tex ture 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.
Procedures
TosetupascenefortheLightTracer:
This is a typical use case.
1. Create the geometr y for an outdoor scene.
2. Add a Skylight (page 2–1149) to illuminate it.
Oneormorespotlightscanalsoworkwell.If
youusethephysicallybasedIESSunorIESSky
lights, using an
exposure control (page 3–289)
is essential.
3. Choose Rendering > Advanced Lighting. On
the Select Advanced Lighting rollout, choose
Light Tracer from the drop-down list.
Active should turn on, and the Parameters
rollout for the Light Tracer should appear.
4. Adjust the Light Tracer parameters,
right-click the viewport you want to render to
make it active, and then click Render Scene.
5. Adjust your rendering settings, and then click
Render .
The scene renders with soft-edged shadows and
color bleeding.