9

Volume Fog Environment Effect 287
Left: Original scene
Right: Increased fog density
Step S ize—Determinesthegranularityofthefog
sampling; the "fineness" of the fog. A large step size
createscoarse(andtosomeextent,aliased)fog.
Max Steps—Limits the amount of sampling s o that
computing the fog doesn’t take forever (literally).
This is especially useful when the fog is of low
density.
When both Step Size and Max Steps have low
values, a liasing results.
Fog Backgr ound—Appliesthefogfunctiontothe
background of the scene.
Noise group
Left: Original scene
Right: Noise added to the fog
Noiseoptionsforvolumefogarecomparableto
the noise options for materials.
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 Threshold—Limits the noise effect. Range=0
to 1.0. When the noise value is above the L ow
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 transition, and thus
produces less potential aliasing (page 3–907).
High—Sets the hi gh threshold.
Low—Sets the low threshold.
Left: Fog with noise
Right: Changing uniformity creates "blobby" fog
Unifor mit y—Ranges from -1 to 1 and acts like
a high-pass filter. The smaller the value, the
more transparent the volume is with discrete
blobsofsmoke. Around-0.3orsoyourimage
begins to look like specks of dust. Because the fog
becomes thinner as this parameter gets sma ller,
you’ll probably need to increase the density or the
volume will start to disappear.
Level s —Sets the number of times the noise is
iteratively applied. Range=1 to 6, including
fractional values. Enabled only for Fractal noise
or Turbulence.
Size—Determinesthesizeofthetendrilsofsmoke
or fog. Smaller values g ive smaller tendrils.