Diffuse

Smooth diffuse material (diffuse)

The smooth diffusematerial (also referred to as “Lambertian”) represents an ideally diffusematerial
with a user-specified amount of reflectance. Any received illumination is scattered so that the surface
looks the same independently of the direction of observation.
Apart from a homogeneous reflectance value, the plugin can also accept a nested or referenced
texturemap to be used as the source of reflectance information, which is thenmapped onto the shape
based on its UV parameterization. When no parameters are specified, the model uses the default of
50% reflectance.
Note that this material is one-sided—that is, observed from the back side, it will be completely
black. If this is undesirable, consider using the twosided BRDF adapter plugin.


Parameter

Parameter Type Description
  • reflectance : spectrum or texture
    • Specifies the diffuse albedo of the material (Default: 0.5)


Rough diffuse material (roughdiffuse)

This reflectance model describes the interaction of light with a rough diffuse material, such as plaster,
sand, clay, or concrete, or “powdery” surfaces. The underlying theory was developed by Oren
and Nayar [35], who model the microscopic surface structure as unresolved planar facets arranged
in V-shaped grooves, where each facet is an ideal diffuse reflector. The model takes into account
shadowing, masking, as well as interreflections between the facets.
Since the original publication, this approach has been shown to be a good match for many realworld
materials, particularly compared to Lambertian scattering, which does not take surface roughness
into account.
The implementation inMitsuba uses a surface roughness parameter α that is slightly different from
the slope-area variance in the original 1994 paper.The reason for this change is tomake the parameter
α portable across different models (i.e. roughdielectric, roughplastic, roughconductor).
To get an intuition about the effect of the parameter α, consider the following approximate classification:
a value of α = 0.001−0.01 corresponds to amaterial with slight imperfections on an otherwise
smooth surface (for such small values, the model will behave identically to diffuse), α = 0.1 is relatively
rough, and α = 0.3 − 0.7 is extremely rough (e.g. an etched or ground surface).
Note that this material is one-sided—that is, observed from the back side, it will be completely
black. If this is undesirable, consider using the twosided BRDF adapter plugin.

Parameter

  • reflectance : spectrum or texture
    • Specifies the diffuse albedo of the material. (Default: 0.5)
  • alpha : spectrum or texture
    • Specifies the roughness of the unresolved surface microgeometry using the root mean square (RMS) slope of the microfacets. (Default: 0.2)
  • useFastApprox : boolean
    • This parameter selects between the full version of themodel or a fast approximation that still retainsmost qualitative features. (Default: false, i.e. use the high-quality version)


  • 最終更新:2014-05-20 16:36:45

このWIKIを編集するにはパスワード入力が必要です

認証パスワード