9

Automatic Exposure Control 295
Automa ti c E x posur e Contr ol
Rendering menu > Environment > Environment and
Effects dialog > Environment panel > Exposure Control
rollout > Choose Automatic Expo sure Control fro m the
list. > Automatic Exposure Control rollout
Auto exp osure can affec t the lighting of the whole im age.
Automatic Exposure Control samples the rendered
image and builds a histogram to give good color
separationacrosstheentiredynamicrangeofthe
rendering. It can enhance some lighting effects
that would otherwise be too dim to see.
Note: A utomatic Exposure Control should not be
used in animations, because every f r ame will have
a different histogram, causing your animation to
flicker.
Impor tant: The mental ray renderer (page 3–78) does not
support the Automatic exposure control.
See also
Environment Panel (page 3–272)
Inter face
B rightness—Adjusts the brightness of the
converted colors. Range=0 to 200. Default=50.
This parameter is animatable.
Co ntrast—Adjusts the contrast of the converted
colors. Range=0 to 100. Default=50.
This parameter is animatable.
Exposure Va lue—Adjusts the overall brightness of
therendering.Range=-5.0to5.0;Negativevalues
make the image darker, and positive values make
it brighter. Default=0.0.
Theexposurevalueiscomparabletotheexposure
compensation setting in cameras with automatic
exposure. This parameter is animatable.
Physical Scale—Sets a physical scale for exposure
cont rol to use with lights that are not physically
based. The result is an adjustment of the rendering
that approximates the eye’s response to the scene.
Each standard light’s Multiplier (page 3–977) is
multipliedbythePhysicalScalevaluetogivea
light intensit y v a lue in candelas. For example,
w ith the default Physical Scale of 1500, a standard
omni light is treated by the renderer and r adiosity
as a photometric isotropic li ght of 1500 candelas.
Physical Scale is also factored into reflections,
refractions, and self-illumination.
Tip: You need to set the Physical Scale when you use
ray-tracing with self illumination. Set this value
to the equivalent of the brightest l ight source in
the scene. This will set the appropriate conve rsion
scale for reflections, self-illumination, and all
other n on-physically based elements a material
offers. In some cases, an object might reflect or
emit more light than the brig htest light object in
the scene; in this case, use the object’s Luminance
value as the Physical Scale.
Range=0.0 to 200,000.0 candelas. Default=1500.0.
Asinglecandleisapproximately1candela(the
unit can also be called a "candle"). A 100-Watt
(W) incandescent light bulb is approximately
139 candelas (cd). A 60W bulb emitting in al l
directions is about 70 cd, while the same bulb with