2012

Table Of Contents
different lighting conditions. The aim is to produce an image on film that is
representative of how that scene would have looked to a human observer.
Presenter includes the Auto Exposure option (see Auto Exposure (page
594)). When enabled, Presenter will render the image twice. Once to sample
the range of luminance values in the output image, then a second time to
render the actual image with the luminance values adjusted to match the
behavior of the human eye.
In general, when using physically accurate lights, the Auto Exposure option
should be on.
Volumetric Lights
Volumetric lighting allows effects such as the scattering of light, by fog or
smoke, in a scene. To use this effect, select the Scattering check box on each
light. A Scattering Medium foreground effect must also be in use (see
Foreground Effects (page 589) for more information).
NOTE You may need to adjust the Medium Density and Medium Ambient
parameters of the Scattering Medium foreground effect to suit your model. If
no volumetric effects are visible, the Medium Density is too low. If the rendered
image is entirely white, the Medium Density is too high.
The default medium is plain white. Optionally, a density shader may be set
to any solid (not wrapped) color shader, to create the effect of a non-uniform
(inhomogeneous) medium. Examples of shaders that can be used are Blue
Marble and Solid Clouds. A shader that has been designed explicitly for
this purpose is the Turbulent shader.
The key points when using volumetric lighting are:
Remember to turn the Scattering parameter of light sources on if you
want to see their volumetric effects.
Use Medium Density and Medium Color to define brightness and color
of the lit medium.
Use a solid color shader set as density shader for simulation of density
variations in the medium.
Decrease the Error Bound parameter, if image appears spotty outside
shadow areas.
Increase the Min LOD parameter, if areas with volumetric shadows appear
spotty.
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