Smooth conductor (conductor)
This plugin implements a perfectly smooth interface to a conductingmaterial, such as ametal. For a similar model that instead describes a rough surface microstructure, take a look at the separately available roughconductor plugin.
In contrast to dielectric materials, conductors do not transmit any light. Their index of refraction is complex-valued and tends to undergo considerable changes throughout the visible color spectrum.
To facilitate the tedious task of specifying spectrally-varying index of refraction information, Mitsuba ships with a set ofmeasured data for severalmaterials, where visible-spectrum information was publicly available 11.
Note that Table 4 also includes several popular optical coatings, which are not actually conductors.
These materials can also be used with this plugin, though note that the plugin will ignore any refraction component that the actual material might have had.There is also a special material profile named none, which disables the computation of Fresnel reflectances and produces an idealized 100% reflecting mirror.
When using this plugin, you should ideally compile Mitsuba with support for spectral rendering to get the most accurate results. While it also works in RGB mode, the computations will be more approximate in nature. Also note that thismaterial is one-sided—that is, observed fromthe back side, it will be completely black. If this is undesirable, consider using the twosided BRDF adapter plugin.
It is also possible to load spectrally varying index of refraction data fromtwo external files containing the real and imaginary components, respectively (see Section 6.1.4 for details on the file format):
11 These index of refraction values are identical to the data distributed with PBRT.They are originally from the Luxpop database (www.luxpop.com) and are based on data by Palik et al.  andmeasurements of atomic scattering factors made by the Center For X-Ray Optics (CXRO) at Berkeley and the Lawrence Livermore National Laboratory (LLNL).
a-C Amorphous carbon
AlAs, AlAs_palik Cubic aluminium arsenide
AlSb, AlSb_palik Cubic aluminium antimonide
Be, Be_palik Polycrystalline beryllium
CsI, CsI_palik Cubic caesium iodide
Cu, Cu_palik Copper
Cu2O, Cu2O_palik Copper (I) oxide
CuO, CuO_palik Copper (II) oxide
d-C, d-C_palik Cubic diamond
Hg, Hg_palik Mercury
HgTe, HgTe_palik Mercury telluride
Ir, Ir_palik Iridium
K, K_palik Polycrystalline potassium
Li, Li_palik Lithium
MgO, MgO_palik Magnesium oxide
Mo, Mo_palik Molybdenum
Nb, Nb_palik Niobium
Rh, Rh_palik Rhodium
Se, Se_palik Selenium
SiC, SiC_palik Hexagonal silicon carbide
SnTe, SnTe_palik Tin telluride
Ta, Ta_palik Tantalum
Te, Te_palik Trigonal tellurium
ThF4, ThF4_palik Polycryst. thorium (IV) fluoride
TiC, TiC_palik Polycrystalline titanium carbide
TiN, TiN_palik Titanium nitride
TiO2, TiO2_palik Tetragonal titan. dioxide
VC, VC_palik Vanadium carbide
VN, VN_palik Vanadium nitride
none No mat. profile (→ 100% reflecting mirror)
Table 4: This table lists all supported materials that can be passed into the conductor and roughconductor plugins. Note that some of them are not actually conductors—this is not a problem, they can be used regardless (though only the reflection component and no transmission will be simulated). In most cases, there are multiple entries for each material, which represent measurements by different authors.
Rough conductor material (roughconductor)
This plugin implements a realistic microfacet scattering model for rendering rough conducting
materials, such as metals. It can be interpreted as a fancy version of the Cook-Torrance model and
should be preferred over heuristic models like phong and ward when possible.
Microfacet theory describes rough surfaces as an arrangement of unresolved and ideally specular
facets, whose normal directions are given by a specially chosenmicrofacet distribution. By accounting
for shadowing and masking effects between these facets, it is possible to reproduce the important offspecular
reflections peaks observed in real-world measurements of such materials.
This plugin is essentially the “roughened” equivalent of the (smooth) plugin conductor. For very
low values of α, the two will be identical, though scenes using this plugin will take longer to render
due to the additional computational burden of tracking surface roughness.
The implementation is based on the paper “Microfacet Models for Refraction through Rough Surfaces”
by Walter et al. . It supports several different types of microfacet distributions and has a
texturable roughness parameter. To facilitate the tedious task of specifying spectrally-varying index of
refraction information, this plugin can access a set ofmeasuredmaterials for which visible-spectrum
information was publicly available (see Table 4 for the full list).There is also a specialmaterial profile
named none, which disables the computation of Fresnel reflectances and produces an idealized 100%
When no parameters are given, the plugin activates the default settings, which describe copper
with a light amount of roughness modeled using a Beckmann distribution.
To get an intuition about the effect of the surface roughness parameter α, consider the following
approximate classification: a value of α = 0.001 − 0.01 corresponds to a material with slight imperfections
on an otherwise smooth surface finish, α = 0.1 is relatively rough, and α = 0.3 − 0.7 is extremely
rough (e.g. an etched or ground finish). Values significantly above that are probably not too realistic.
When rendering with the Ashikhmin-Shirley or Phong microfacet distributions, a conversion is used
to turn the specified α roughness value into the exponents of these distributions. This is done in a
way, such that the different distributions all produce a similar appearance for the same value of α.
The Ashikhmin-Shirley microfacet distribution allows the specification of two distinct roughness
values along the tangent and bitangent directions. This can be used to provide a material with a
“brushed” appearance. The alignment of the anisotropy will follow the UV parameterization of the
underlying mesh in this case.This also means that such an anisotropic material cannot be applied to
triangle meshes that are missing texture coordinates.
When using this plugin, you should ideally compile Mitsuba with support for spectral rendering
to get the most accurate results. While it also works in RGB mode, the computations will be more
approximate in nature. Also note that thismaterial is one-sided—that is, observed fromthe back side,
it will be completely black. If this is undesirable, consider using the twosided BRDF adapter.
Parameter Type Description
- distribution : string
- Specifies the type of microfacet normal distribution used to model the surface roughness.
- (i) beckmann: Physically-based distribution derived from Gaussian random surfaces.This is the default.
- (ii) ggx: New distribution proposed byWalter et al. , which ismeant to better handle the long tails observed inmeasurements of ground surfaces. Renderingswith this distribution may converge slowly.
- (iii) phong: Classical cosp θ distribution. Due to the underlying microfacet theory, the use of this distribution here leads to more realistic behavior than the separately available phong plugin.
- (iv) as: Anisotropic Phong-style microfacet distribution proposed by Ashikhmin and Shirley .
- alpha : float or texture
- Specifies the roughness of the unresolved surface microgeometry. When the Beckmann distribution is used, this parameter is equal to the root mean square (RMS) slope of the microfacets. This parameter is only valid when distribution=beckmann/phong/ggx. (Default: 0.1).
- alphaU, alphaV : float or texture
- Specifies the anisotropic roughness values along the tangent and bitangent directions. These parameter are only valid when distribution=as. (Default: 0.1).
- material : string
- Name of amaterial preset, seeTable 4.(Default: Cu / copper)
- eta, k : spectrum
- Real and imaginary components of the material’s index of refraction (Default: based on the value of material)
- extEta : float or string
- Real-valued index of refraction of the surrounding dielectric, or a material name of a dielectric (Default: air)
- specular Reflectance : spectrum or texture
- Optional factor that can be used to modulate the specular reflection component. Note that for physical realism, this parameter should never be touched. (Default: 1.0)