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1566 Chapter 16: Material Editor, Materials, and Maps
• Transparency takes energy from diffuse; that is,
at 100% t ransparency, there is no diffuse at all.
• Reflectivity takes energy from both diffuse and
transparency; that is, at 100% reflectiv ity there
is neither diffuse nor transparency.
• Translucency is a type of transparency, and the
Translucency Weight parameter defines the
percentage of transparency vs. translucency.
From left to right: Reflectivity =0.0, 0.4, 0.8, and 1.0
From left to right: Transparenc y=0.0, 0 .4, 0.8, and 1.0
Conservation of energy also means that the level of
highlights is linked to the glossiness of a surface. A
high Reflection Glossiness value causes a narrow,
intense h ig h light, while a lower value causes a
wider, less intense highlig ht. This is bec ause the
energy is now spread out and dissipated over a
larger area.
BRDF - how reflectivity depends on a ngle
In the real world, the reflect ivity of a surface is
often view-angle dependent. A fancy term for this
is bidirectional reflectance distribution function
(BRDF); that is, a way to define how much a
material reflects when se en from various angles.
The reflectivity of the wood floor depends on the view angle.
Many materials exhibit this behavior. The most
obviousexamplesareglass,water,andother
dielectric materials with Fresnel effects (where
the angular dependency is guided strictly by the
index of refraction), but other layered materials
such as lacquered wood and plastic display sim ilar
characteristics.
The Arch & Design material allows this effect to be
definedbytheindexofrefraction,andalsoallows
an explicit setting for the two reflectivity values for:
• 0 degree faces (surfaces directly facing the
camera)
• 90 deg ree faces (surfaces 90 degrees to the
camera)
For more information, see BRDF rollout (page
2–1554).
Reflectivity features
The final surface reflectivity is in reality caused by
the sum of three components:
• The diff use effect
•Theactualreflections
• Specular highlights that simulate the reflection
of light sources
Diffuse, reflections, and highlights
In the real world, hig h lights are just glossy
reflections of the light sources. In computer
gr aphics it’s more efficient to t reat these separately.
However, to maintain physical accuracy the
material automatically keeps highlight intensity,
glossiness, anisotropy, etc. in sync with the
intensit y, g lossiness and anisotropy of reflections.
Thus,therearenoseparatecontrolsfortheseas
both are driven by the reflectivity sett ings.