Dielectric coating

Smooth dielectric coating (coating)

This plugin implements a smooth dielectric coating (e.g. a layer of varnish) in the style of the paper “Arbitrarily LayeredMicro-Facet Surfaces” byWeidlich andWilkie [52]. Any BSDF inMitsuba can be coated using this plugin, and multiple coating layers can even be applied in sequence. This allows designing interesting custommaterials like car paint or glazedmetal foil.The coating layer can optionally be tinted (i.e. filled with an absorbing medium), in which case this model also accounts for the directionally dependent absorption within the layer.
Note that the plugin discards illumination that undergoes internal reflection within the coating.
This can lead to a noticeable energy loss for materials that reflect much of their energy near or below the critical angle (i.e. diffuse or very rough materials). Therefore, users are discouraged to use this plugin to coat smooth diffuse materials, since there is a separately available plugin named plastic, which covers the same case and does not suffer from energy loss.

Technical details
Evaluating the internal component of this model entails refracting the incident and exitant rays through the dielectric interface, followed by querying the nestedmaterialwith thismodified direction pair.The result is attenuated by the two Fresnel transmittances and the absorption, if any.


Parameter Type Description

  • intIOR : float or string
    • Interior index of refraction specified numerically or using a known material name. (Default: bk7 / 1.5046)
  • extIOR : float or string
    • Exterior index of refraction specified numerically or using a known material name. (Default: air / 1.000277)
  • thickness : float
    • Denotes the thickness of the layer (to model absorption — should be specified in inverse units of sigmaA) (Default: 1)
  • sigmaA : spectrum or texture
    • The absorption coefficient of the coating layer. (Default: 0, i.e. there is no absorption)
  • 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)
  • (Nested plugin) : bsdf
    • A nested BSDF model that should be coated.





Rough dielectric coating (roughcoating)

This plugin implements a very approximate 12 model that simulates a rough dielectric coating. It is essentially the roughened version of coating. Any BSDF in Mitsuba can be coated using this plugin andmultiple coating layers can even be applied in sequence,which allows designing interesting custom materials. The coating layer can optionally be tinted (i.e. filled with an absorbing medium), in which case this model also accounts for the directionally dependent absorption within the layer.
Note that the plugin discards illumination that undergoes internal reflection within the coating.
This can lead to a noticeable energy loss for materials that reflect much of their energy near or below the critical angle (i.e. diffuse or very rough materials).
The implementation here is influenced by the paper “Arbitrarily LayeredMicro-Facet Surfaces” by Weidlich andWilkie [52].

12 Themodel only accounts for roughness in the specular reflection and Fresnel transmittance through the interface. The interior model receives incident illumination that is transformed as if the coating was smooth. While that’s not quite correct, it is a convenient workaround when the coating plugin produces specular highlights that are too sharp.

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. [48], 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.
  • 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. (Default: 0.1).
  • intIOR : float or string
    • Interior index of refraction specified numerically or using a known material name. (Default: bk7 / 1.5046)
  • extIOR : float or string
    • Exterior index of refraction specified numerically or using a known material name. (Default: air / 1.000277)
  • thickness : float
    • Denotes the thickness of the layer (to model absorption — should be specified in inverse units of sigmaA) (Default: 1)
  • sigmaA : spectrum or texture
    • The absorption coefficient of the coating layer. (Default: 0, i.e. there is no absorption)
  • 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)
  • (Nested plugin) : bsdf
    • A nested BSDF model that should be coated.




  • 最終更新:2014-05-21 10:33:48

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