9

Reflectance and Transmittance Display 1431
RGB Level value in the bitmap ’s Output rollout
(page 2–1621).
Left: Wood grain bitmap as originally photographed has
too high a reflectance.
Right: Reducing the RGB Level value reduces the map’s
reflectance.
Inter face
Reflectance—Reflectance is the percentage of
diffuse light energy that is reflected from a
material. When you increase a material’s HSV
value (V), the material reflects more diffuse light.
Decreasing a material’s Opacity also decreases its
reflectance.
Typically, the reflectance of a material should never
be g reater than 85%. this is an unusually high
value that will lead to poor-quality renderings. In
the real world, even the whitest wall reflects no
more than 80% of the light it receives.
Onesourceofhighreflectancecanbeamap
assigned to the material’s diffuse component. For
example, a white tile bitmap might create high
reflectance. In this case, you can reduce reflectance
by reducing the RGB Level in the bitmap’s Output
rollout.
An alternate way to reduce a bitmapped material’s
reflectance is to set the diffuse color of the material
to black, and then reduce the diffuse map’s
Amount (in the parent material’s Maps rollout
(page 2–1474)). You can use this method to
reduce the reflectance of 3D procedural maps (page
2–1662) as well.
Herearesometypicalreflectancerangesfor
common materials:
Mater ial Minimum Maximum
Ceramic
20% 70%
Fabric
20% 70%
Masonry
20% 50%
Metal
30% 90%
Paint
30% 80%
Paper
30% 70%
Plastic
20% 80%
Stone
20% 70%
Wood
20% 50%
Trans mittance—Transmittance is the amount of
light energ y tr ansmitted through a material. A
completely opaque material has 0% transmittance.
When t he material is transparent (like clear glass),
the energy transmitted is specular, and light
passes directly through the material (subject to
refraction). The value of specular transmittance is
an interaction between the material’s Opacity value
(page 2–1488) and its filter color (page 3–939).
When the filter color is pure w hite, specular
transmittance is the inverse of Opacity.
When the material is translucent (like frosted
glass), t he energy t r ansmitted is diffuse, and
scattered in a ll directions. The value of diffuse
transmittance is based on the HSV value (V)
of the translucent color (page 2–1491).Diffuse
transmittance happens only for materials that use
the Translucent shader (page 2–1484),orRaytrace
materials (page 2–1512),thatspecifytranslucency.
Usually, when a material has high transmittance, it
has low reflect a nce, and the other way around.