9

298 Chapter 18: Effects and Environments
3–78). Logarithmic Exposure Control is best for
scenes with a very high dynamic range.
Left: The intensity of an IES Sun light completely overexposes a
scene.
Right: Logarithmic exposure control corrects the overexposure.
Logarithmic Exposure Control is the best type of
exposure control for animations because it doesn’t
use h istograms.
Tip: If you’re rendering to texture (page 3–144),
use the Logarithmic exposure control, n ot the
AutomaticorLinearcontrol.
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.
Mid Tones—Adjusts the mid-tone values of
the converted colors. Range=0.01 to 20.0.
Default=1.0.
This parameter is animatable.
Adjusting the value of mid tones
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.
Note: The mental ray renderer treats Physical Scale
inthesamewaythescanlinerendererdoesin