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Automatic Exposure Control 291
Automa ti c E xp osur e Control
Rendering menu > Environment > Environment and
Effects dialog > Environment panel > Exposure Control
rollout > Choose Automatic Exposure Contro l from the
list. > Automatic E xposure Control rollou t
Auto exposure can affect the lighting of the whole image.
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: Automatic Exposure Control should not be
used in animations, because every fr ame will have
a different histogram, causing your animation to
flicker.
Impor tant: The mental ray renderer (page 3–77) does
not support the Automatic exposure control.
See also
Environment Panel (page 3–268)
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 camer as with automatic
exposure. T his parameter is animatable.
Physical Scale—Sets a physical scale for exposure
cont rol to u se with lights that are not physically
based. The result is an adjust ment of the rendering
that approximates the eye’s response to the scene.
Each standard light’s
Multiplier (page 3–1071)
is multiplied by the Physical Scale value to give
a light intensit y value in candelas. For example,
w ith the default Physical Scale of 1500, a standard
omni lig ht is treated by the renderer and radiosity
as a photometric isotropic li g ht of 1500 candelas.
Physical Scale is also factored into reflections,
refractions, and self-illumination.
Tip: You need to set the Physical Scale w hen you u s e
ray-tracing with self il lumination. Set this value
to the equivalent of the brightest light source in
the scene. This will set the appropriate conve rsion
scale for reflections, self-illumination, and all
other non-physically based elements a material
offers. In some cases, an object might reflect or
emit more light than the brightest li ght 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 all
directions is about 70 cd, while the same bulb with