9

994 Glossary
squaremeterorcandelaspersquareinch. The
candela w as original ly defined as the luminous
intensity emitted by a single wax candle.
Finally, luminous intensity is the light energy per
unit time emitted by a point source in a particular
direction. The u nit of measure of luminous
intensity is the candela. Luminous intensity is
used to describe the directional distribution of a
light source, that is, to spe cify how the luminous
intensity of a light source varies as a function of
the outgoing direction.
Because3dsMaxworkswiththesephysicallybased
photometric values, it can accurately simulate
real-world lighting and materials.
Photon M ap
A photon map™ is a technique to generate the
indirect illumination effects of caustics (page 3–92)
and global illumination (page 3–93) when you
render with the mental ray renderer (page 3–78).
When it calculates indirect illumination, the
mental ray renderer traces photons emitted from
a lig ht. T he photon is traced through t he scene,
being reflected or tr ansmitted by objects, until it
strikes a diffuse sur face. When it st rikes a surface,
the photon is stored in the photon map.
Generating photon maps is time-consuming. To
improve performance, you must explicitly specify:
• Which lights emit photons for indirect
illumination.
• Which objects can generate caustics or global
illumination.
• Which objects can receive caustics or global
illumination.
The settings for generating and receiving caustics
are on the Objec t Properties di alog > mental ray
Panel (page 1–126).
The photon map stores photons only for objects
that can receive caustics, g lobal i l lumination, or
both.
To further reduce the time required to generate
a photon map, photons are limited by the Trace
Depth controls. These limit the number of times a
photon can be reflected, refracted, or both.
Inanimations,anotherwaytosavetimeistoreuse
the photon-map file. If lighting doesn’t change
over the course of an animation, use the Photon
Map controls (page 3–109).
The mental ray renderer saves photon maps as
PMAP files (page 3–995).Photonmapcontrols
are on the Render Scene Dialog > Indirect
Illumination panel > Caustics And Global
Illumination rollout (page 3–106).
PHY Files
Yo u c a n s a v e Physique (page 2 –1076) data to a
Physique (PHY) file. This saves data common to
allobjectsthatshareagivenPhysiquemodifier.
Later, you can reload the PHY file, either to restore
the data that belongs to a particular skin or portion
of skin, or to transfer the Physique of one skin (or
portionofit)toadifferentone.
Physique
Physique (page 2–1076) is a modifier that, when
applied to a mesh , allows the movements of
an underlying skeleton to seamlessly move t he
mesh like bones and muscle under a human skin.
Physique will work on any point-based object,
including geometric primitives, editable meshes,
patch-based objects, NURBS, and FFD space
warps. It will attach to any sk eleton structure,
including a biped (page 2–843),bones,splines,or
any hierarchy.