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58 Chapter 17: Rendering
Lighting Analysis
After you generate a radiosity solution, you can
use the
Lighting Analysis tool (page 3–75) to
analyze the lighting levels in your scene. This
dialog provides data on material reflectance,
transmittance, and luminance.
You can also interactively visualize the light levels
in the scene by using the
Pseudo Color Exposure
Cont rol (page 3–296)
. Rendering to a rendered
frame window displays an additional rendered
frame with a legend below the image. The legend
correlates lighting levels and color values.
If you need to generate a lighting report, you
can use the
Lighting Data Exporter utility (page
3–299)
to export the luminance and illuminance
data to a 32-bit LogLUV
TIFF file (page 3–684)
or a pair of PIC files (page 3–677) (one each for
luminance and illuminance).
Note: To obtain the most accurate quantitative
analysis of lighting levels, you should avoid using
colored materials and diffuse maps.
Non-Physically Based Work flow
You don’t necessarily have to work with physically
based lights and materials in order to incorporate
radiosity effects into your renderi ngs . But there
are a number of issues that you need to consider:
• Lights: Because the radiosity eng ine is
physically based,
Standard lights (page 2–1142)
areinterpretedbytheengineas Photometric
lights (page 2–1155)
.Forexample,aStandard
Spot light with a multiplier value of 1.0 will be
translated as a Physical ly Based Spot light with
an intensity value of 1500 candelas (default
value). This translation value corresponds to
the Physical Scale value in t he various exposure
controls.
In addition, if your Standard lights use
custom attenuation settings (for example, no
attenuation, manual attenuation, or linear
decay), the radiosity engine will always solve
for these lights using the physically correct
InverseSquareattenuation. Thismeansthat
theamountofenergythatbouncesbetween
surfaces might not be equivalent to the w ay the
Standard lights render .
• Natural Lighting: To simulate natural lighting
w ithout using the physically based workflow
described above, you can only use a
Direct Lig ht
(page 2–1145)
for the Sun and Skylight (page
2–1149)
to produce skylight (page 3–1106) .
• Exp osu r e Cont r ol: Since Standard lights are
not physically based, you should only use
exposure controls for the radiosity solution.
Use the
Logarithmic Exposure Control (page
3–293)
, making sure to turn on Affect Indirect
Only. The Brightness and Contrast controls
oftheexposurecontrolwillonlyaffectthe
radiosity solution and your lights will render
as usual.
To process radiosity with standard lighting:
1.
Ensure that your geometry is set to a physically
correct scale.
2. OntheCreatepanel,clickLights.
Create and position
standard lights (page
2–1142)
in your scene.
3. Click Render Scene to preview the
lighting. At this stage, the radiosity will not be
processed, but you can quickly confirm that the
direct lig hting is correct. Adjust the position
of the lights if desired.
4. Choose Rendering > Advanced Lighting >
Radiosity. Make sure that Active is turned on.
5. On the Radiosity Parameters rollout, click
Start to process radiosit y. Once the Radiosity
calculation has been completed, you should see
your results in the viewports.