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292 Chapter 18: Effects and Environments
casts light much farther than it actually glows.
Default=100.
Left: Original scene
Right: Attenuation limits the range of the light.
Noise group
Noise On—Turns the noise on and off. When noise
is on there is a slight increase in render time.
Amount—Thepercentageofnoiseappliedtothe
fog. If the amount is 0, there is no n oise. If the
amountis1,thefogbecomespurenoise.
Left: Original scene
Right: Noise added
Link To Light—Links the noise effect to its light
object, rather than to world coordinates.
Usuallyyouwantnoisetolooklikefogordust
motes in the atmosphere, in which case, as the light
moves, the noise should remain with the world
coordinates. For cer tain special effects, however,
you might want the noise l in ked to the light’s
coordinates. In these cases, turn on Link to Light.
Ty pe—Choose one of three types of noise to apply.
•
Regular—The standard noise pattern.
•
Fr actal —An iterative fractal noise pattern.
•
Tu rbulence —An iterative turbulence pattern.
Inver t—Reverses the noise effect. Dense fog
becomes translucent and vice versa.
Noise Thr eshold—Limits the noise effect. When the
noise value is above the Low threshold and below
the High threshold, the dynamic range stretches
to fill 0-1. This makes for a smaller discontinuity
(first order instead of 0 order) at the threshold
transitionandthusproduceslesspotentialaliasing
(page 3–907).
•
High—Sets the high threshold. Range=0 to 1.0.
•
Low—Sets the low threshold. Range=0 to 1.0.
Unifor mit y—Acts like a high-pass filter: the smaller
thevalue,themorethevolumeistransparent
with discrete blobs of smoke. By around -0.3 or
so your image beg ins to look like specks of dust.
Because the fog becomes thinner as this parameter
gets sma l ler, you’ll probably need to increase the
density or the volume will start to disappear.
Range=-1 to 1
Level s —Sets the number of times the noise is
iteratively applied. This parameter is animatable.
Enabled only for F ractal noise or Turbulence.
Range=1 to 6, including fractional values.
Size—Determinesthesizeofthetendrilsofsmoke
or fog. Smaller values g ive smaller tendrils.
Left: Volume light with noise
Right: Reducing the size value