produces a RADIANCE scene description of distant illum
sources corresponding to bright, concentrated regions in
the given ambient environment.
Any local geometry is ignored in the input octree, which
should be derived from a captured light probe and modeled
as a distant hemispherical or spherical glow source.
The output sources may then be combined with this environment
to produce a more efficient scene for rendering, faster and
less prone to sampling artifacts.
option may be used to specify the number of ray samples, which
defaults to 262,000.
Calculation time is roughly proportional to this setting, and the
default is fine enough to resolve sources the size of the sun
(half a degree) or larger.
option may be used to manually set the radiance threshold for
sources, in watts/sr/meter^2.
The default uses the top 2 percentile of the environment, which
is usally a good value.
option may be used to specify a maximum source diameter,
which defaults to 15 degrees.
silently enforces a maximum of 180 degrees for this option.
If no input octree is specified, the standard input is read.
To add sources with a maximum size of 20 degrees
to the enviornment described in environ.oct: