8

Volume Fog Environment Effect 283
Left: Original scene
Right: Increased fog density
Step Size—Determinesthegranularityofthefog
sampling; the "fineness" of the fog. A large step size
createscoarse(andtosomeextent,aliased)fog.
Max Steps—Limits the amount of sampling so 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 Backgroun d—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 act al—An iterative fractal noise pattern.
Tu rb ulence—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 Low
threshold and below the High threshold, the
dynamic range stretches to fill 0-1. This makes
for a smaller discon tinuity (First order instead
of 0 order) at the threshold transition, and thus
produces less potential
aliasing (page 3–1001) .
High—Sets the high 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, t he
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 smaller,
you’ll probably need to increase the densit y or the
volume will start to disappear .
Level s —Sets the number of times the noi se is
iteratively applied. Range=1 to 6, including
fractional values. Enabled only for Fractal noise
or Turbulence.
Size—Determinesthesizeofthetendrilsofsmoke
or fog. Smaller values give smaller tendrils.