8
Caustics and Global Illumination Rollout (mental ray Renderer) 107
To get good results, you might need to turn on
MaximumSamplingRadiusandincreasethe
photon size.
Volumes group
Thecontrolsinthisgroupandtheonesthatfollow
are for the
photon maps (page 3–1088)
used to
calculate caustics and global illumination. This
group controls volumetric caustics. Volumetric
caustics require a material to have a volume shader
assign to its Photon Volume component.
Ma xi mum Num. Photons per Sa mple—Sets how
many photons are used to shade the volu me.
Default=100.
Max imum Sampling R adius—When the check box
is on, the spinner sets the size of photons. When
off, each photon is calculated to b e one-tenth the
size of the
scene extents (page 3–1101)
.Default:
check b ox=off; value=1.0.
This spinner is u navailable if the check box is
turned off.
Photon M ap group
These controls tell mental ray how to calculate the
photon map for indirect illumination.
Rebuild (Do Not Re-Use Cache)—If Rebuild is turned
on, the renderer saves the recalculated photon
map to the file specified by the Browse button.
Default=on.
•
Use File—When on, the mental ray renderer
either saves the photon map to a
.pmap file
(page 3–1089)
,orloadsanexistingfile. The
state of Rebuild determines whether the .
pmap
file is saved or loaded.
This option is unavailable unless you click
Browse (“...”) to provide a name for the .
pmap
file.
•
Browse (“ ...” )—Click to display a file selector
dialog , which lets you specify a name for the
photon map (.
pmap)
file, and the folder where
it is sav ed.
•
File name—When you have used the Sav e
button to specify a photon map file, the name
field displays its name and path.
•
Delete File—Click to delete the current
.
pmap
file.
Trace Depth group
The Trace D epth controls are similar to those for
calculating reflections and refractions, but they
refer to the photons used by caustics and global
illumination, r ather than to light r ays used in
diffuse reflection and refraction.
Max. Depth—Limits the combination of reflection
and refraction. Reflection and refraction of a
photon stop when the total number of both equals
the Maximum Depth setting. For example, if
Maximum Depth equals 3 and the tr ace depths
each equal 2, a photon can be reflected twice
and refracted once, or vice versa, but it can’t be
reflected and refracted four times. Default=5.
Max. R eflections—Sets the number of times a
photon can be reflected. At 0, no reflection occurs.
A t 1, the photon can be reflected once only. At
2, the photon can be reflected twice, and so on.
Default=5.
Max. R ef ractions—Sets the number of t imes a
photon can be refracted. At 0, no refraction
occurs. At 1, the photon can b e refracted once
only. At 2, the photon can be refracted twice, and
so on. Default=5.
Light Propert ies group
Cont rols in this group affect how lights behave
when ca lculating indirect illumination. By default,
the energy and photon sett ings apply to all li ghts in
ascene.Usethe
mental ray Indirect Illumination
rollout (page 2–1187)
for light objects to adjust an
individual light either by multiplying the global