2009

Table Of Contents
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, "Auto Exposure" should be on.
Volumetric Lights
Volumetric lighting allows effects such as the scattering of light, by fog or smoke, in a scene. Enable the
"Scattering" check box on each light. A "Scattering Medium" foreground effect must also be in use (see
Foreground Effects for more information on how to setup foreground effects).
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 Colour" to define brightness and colour of the lit medium.
Use a solid color shader set as "Density Shader" for simulation of density variations in the medium.
Decrease "Error Bound" if image appears spotty outside shadow areas.
Increase "Min LOD" parameter if areas with volumetric shadows appear spotty.
Set high "Error Bound" and small "Min LOD" for fast previews.
Use "Inverse Square Law" for your light's "Fall Off", together with auto exposure, for best results.
Image-based Lighting
Image-based lighting, simply put, is where an image is used to light a scene. In the real world, every
object is lit not only by light sources like the sun, lamps etc, but also by everything around. Standing in the
middle of a street, a person will be lit by the sun, the blue sky, the brown buildings and the grey floor.
Emulating this form of lighting clearly has the potential to create incredibly realistic images.
Images used in this lighting method are a special kind of image called a High Dynamic Range Image or
HDRI. This type of image has the capability of lighting a scene with incredible accuracy. In Presenter an
HDRI is wrapped around the scene as a sphere, and colour and brightness from the HDRI are cast onto
the 3D model to light it.
To give an example of the difference this can make, this is a before shot using normal lights
Presenter Lighting
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