9

Exposure Controls 293
Phase—
Cont rols the speed of the wind. If you
have Wind Strength also set to greater than 0, the
fogvolumeanimatesinaccordancewiththewind
direction. With no Wind Strength, the fog churns
in place. Because there’s an animation track for
phase, you can use the Function Curve editor to
define precisely how you want your wind "gusts"
to happen.
Wind moves the fog volume in the specified
direction over time. Wind is tied to the phase
parameter so as the phase changes, the wind
moves. If Phase isn’t animated there will be no
wind.
Wind S trength—Controls how fast the smoke
moves away from the wind direction, relative to
phase. As mentioned above, if the phase is n ot
animated then the smoke won’t move, regardless
of the wind strength. By having the phase animate
slowly with a large wind strength, the fog moves
more than it chur ns.
Alternatively, if the phase changes rapidly while
the wind strength is relatively small, the fog will
churn fast and drift slowly. If you want the fog to
justchurninplace,animatethephasebutkeep
wind strength at 0.
Wind from the—Defines the direction the wind is
coming from.
Exposure Controls
Rendering menu > Environment > Environment and
Effects dialog > Environment panel > Exposure Control
rollout
Exposure Controls are plug-in components that
adjust the output levels and color range of a
rendering, as if you were adjusting film exposure.
Exposure Controls are especially useful for
renderings that use radiosit y (page 3–51).
Exposure control compensates for the limited
dynamic range of monitors. Monitors have a
dynamic range of about two orders of magnitude.
The brightest color that appears on a display is
about 100 times brighter than the di m m est. The
eye, by comparison, can perceive a dy namic range
of about 16 orders of magnitude. The brightest
color we can perceive is about 10 million-billion
times brighter than the dimmest. Exposure control
adjustscolorssotheybettersimulatetheeye’s
great dynamic range, whi le still fitting within the
color range that can be rendered.
• Automatic Exposure Control (page 3–295)
samples the rendered image and builds a
histogram to g ive good color separat ion across
theentiredynamicrangeoftherendering.It
can enhance some lighting effects that would
otherwisebetoodimtosee.
• Linear Exposure Control (page 3–296) samples
the rendering and uses the average brightness
of the scene to map physical values to RGB
values. Linear E xposure Control is b e st for
scenes with a fairly low dynamic range.
• Logarithmic Exposure Control (page 3–297) uses
brightness, contrast, a nd whether the scene is
outdoors in daylight to map physical values to
RGB values. Logarithmic Exposure Control
is better for scenes with a very high dynamic
range.
• Pseudo Color Exposure Control (page 3–300)
is actually a lighting analysis tool. It maps
luminances to pseudo colors that show the
brightness of the va lues b eing converted.
Impor tant: The mental ray renderer (page 3–78) supports
only th e Logarithmic and Pseudo Color exposure
controls.