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106 Chapter 17: Rendering
Enable—
When on, the mental ray renderer
calculates caustic effects. Default=off.
Ma xi mum Num. Photons per Sa mple—Sets how
many photons are used to compute the intensity of
thecaustic.Increasingthisvaluemakescaustics
less noisy but also more blurry. Decreasing this
value m a kes caustics more noisy but less blurry.
The larger the Samples value, the greater the
rendering time. Default=100.
Tip: To preview a caustic, set Samples to 20, then
increase the va lue for a final rendering.
Max imum S ampling R adius—When on, the spinner
value sets t he size of photons. When off, each
photon is calculated to be 1/100 of the radius
of the full scene. Maximum Sampling Radius
default=off; spinner default=1.0.
In many cases, the default photon size
(Radius=off) of 1/100 the scene size gives useful
results. In other cases, the default photon size
mightbetoolargeortoosmall.
When photon reflections overlap, the mental ray
renderer uses sampling to smooth them together.
Increasing the number of samples increases
the a mount of smoothing and can create more
natural-looking caustics. When photons have a
small radius and don’t o verlap, the Samples setting
hasnoeffect. LowRadiusvalueswithalarge
number of photons result in dotty caustics.
Filter—Sets the filter to use for sharpening caustics.
Can equal Box, Cone, or Gauss. The B ox option
requires less rendering time. T he Cone option
makescausticsappearsharper.Default=Box.
The G auss filter u ses a Gauss (bell) curve, and can
be smoother than the Cone fi lter.
Kernel—Controls the sharpness of c austics when
youchooseConeasthecausticfilter.Thisvalue
must be greate r than 1.0. Increasing the Kernel
value m akes caustics more blurry. Decreasing
theKernelvaluemakescausticssharper,butalso
slightly more noisy. Default=1.1.
Opaque Shadows when Caustics Are
Enabled—
When on, shadows are opaque.
When off, shadows can be part ially transparent.
Default=on.
Opaque shadows render more quickly than
transparent shadows.
Global I llumination (GI) group
Enable—When on, the mental ray renderer
calculates
global illumination (page 3–92) .
Default=off.
Ma xi mum Num. Photons per S ample—Sets how
many photons are used to compute the intensity
of the global illumination. Increasing this value
makes global illumination less noisy but also
more blurry. Decreasing this value makes global
illuminat ion more noisy but less blurry. The larger
the Samples value, the greater the rendering time.
Default=500.
Tip: To preview global illumination, set Samples to
100, then increase the value for a final rendering.
Maximum S ampling R adius—When on, the spinner
value sets the size of photons. When off, each
photon is calculated to be 1/10 of the radius
of the full scene. Maximum Sampling Radius
default=off; spinner default=1.0.
In many cases, the default photon size (Maximum
Sampling R ad ius= off) of one-tenth the scene size
gives useful results. In other cases, the default
photon size might be too large or too small.
When photons overlap, the mental ray renderer
uses sampling to smooth them together. Increasing
the number of samples increases the amount of
smoothingandcancreatemorenatural-looking
caustics. When photons have a small radius and
don’t overlap, the Samples setting has no effect.
For global illumination, photons should overlap.