8

Physical Qualities Rollout 1379
Trans parency—
Controls how transparent the
material is. This value is a percentage: at 100.0,
the material is completely transparent; at lower
values, the material is partly opaque; and at 0.0,
the material is completely opaque.
Tip: The effect of transparency is best previewed
against a pattern background. If the material
preview doesn’t show a pattern of colored checks,
right-click the material preview or the map
preview,andchooseBackgroundfromthepop-up
menu.
The amount spinner for a transparency map scales
the map. If no map is assigned, the spinner value
is used by itself.
Trans lucency—Controls how translucent the
materialis.Atranslucentobjecttransmitslight,
butalsoscattersitwithintheobject.Thisvalue
is a percentage: at 0.0, the material is completely
opaque; at 100.0, the material is as tr a nslucent as
possible.
The amount spinner for a translucency map scales
the map. If no map is assigned, the spinner value
is used by itself.
Index of Refraction—The index of refraction
(IOR)controlshowseverelythematerialrefracts
transmitted light, and how reflective the material
appears. At 1.0, the IOR of air, the object behind
thetransparentobjectdoesnotdistort.At1.5,the
object behind distorts greatly, l ike a glass marble.
Range=1.0 to 2.5.
Common IORs (assuming the camera is in air or a
vacuum) are:
Material IOR Value
Vacuum
1.0 (exactly)
Air
1.0003
Water
1.333
Glass
1.5 to 1.7
Diamond
2.419
In the physical world, the IOR results from the
relative speeds of light through the transparent
material and the medium the eye or the camera is
in. Typically this is related to the object’s density:
the higher the IOR, the denser the object.
The IOR affects how shiny a material appears;
or, in the case of transparent materials such as
water or glass, the amount of distortion. For
nontra nsparent materials, the higher the IOR , the
more light is reflected from the material, and the
shinier the material appears.
A refractive index of 1.0 means that all l ight is
transmitted into the material. In this case, even if
the m aterial has a high Shininess value, the surface
appears perfectly diffuse, and shows no specular
highlights.
Luminance cd/m2 —When its luminance is greater
than 0.0, the material appears to glow, and if you
turn on Emit Energy (see below), it contributes
energy to the
radiosity solution (page 3–50) .
Luminance is measured in candelas per meter
squared.
The amount spinner for a luminance map scales
the map. If no map is assig ned, the spinner value
is used by itself.
Set luminance fr om light—Obtains the
material’s luminance from a light in the scene.
Clicktoturnonthisbutton,thenclickalightina
viewport. The material’s luminance is set to match
the luminance of the light, and the button is turned
off once more.
2-Sided—When on, makes the material 2-sided
(page 3–995)
. Applies the m aterial to both sides of
selected faces.
Raw Diffuse Texture—When on, excludes the
material from lighting and exposure control. This
makes the material render with a completely flat
look, using the pure RGB values of the diffuse
color or map. Default=off.