8

Exposure Controls 289
Phase—
Cont rols the speed of the wind. If you
have Wind Streng th also set to greater than 0, the
fogvolumeanimatesinaccordancewiththewind
direction. With no Wind Strength, the fog churns
in place. Because t here’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 not
animated then the s moke won’t move, regardless
of the wind s trength. By having the phase animate
slowly with a large wind strength, the fog moves
more than it churns.
Alternatively, if the phase changes rapidly while
the wind strength is relatively small, the fog will
churn fast and dr ift 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
radiosity (page 3–50) .
Exposure control compensates for t he 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 br ighter than the d im mest. The
eye, by comparison, can perceive a dynamic r ange
of about 16 orders of magnitude. The brightest
color we can perceive is about 10 million-bi llion
times brighter than the dimmest. Exposure control
adjustscolorssotheybettersimulatetheeye’s
great dynamic range, while sti ll fitt ing within the
color range that can be rendered.
•
Automatic Exposure Control (page 3–291)
samples the rendered image and builds a
histogram to give good color separation across
theentiredynamicrangeoftherendering.It
can enhance some lighting effects that would
otherwisebetoodimtosee.
•
Linear Exposure C ontrol (page 3–292) samples
the rendering and uses the average brightness
of the scene to map physical values to RGB
values. L inear Exposure Control is best for
scenes w ith a fairly low dy namic range.
•
Logarithmic Exposure Control (page 3–293)
uses brightness, contrast, and whether the
sceneisoutdoorsindaylighttomapphysical
values to RGB values. Logarithmic Exposure
Cont rol is better for scenes with a very high
dynamic range.
•
Pseudo Color Exposure Cont rol (page 3–296)
is actually a lighting analysis tool. It maps
luminances to p s eudo colors that show the
brightness of the values being converted.
Impor tant: The mental ray renderer (page 3–77)
supports only the Logarithmic and Pseudo Color
exposure controls.