Medium tab

True volumetric scattering is supported and Thea Render can solve light transport problems that include participating media. There are a lot of possibilities since mediums can be both homogeneous and a lot of supported phase functions.

  • Absorption color: Defines the transmittance color ‐ this is actually the color visualized after a distance of 1 meter (assuming unit density and no scattering). When the distance is less than 1 meter, the color shifts towards white and when the distance gets bigger, the transmittance shifts towards black. The color change with distance is strongly non‐linear and thus it is recommended to avoid highly saturated colors.
  • Absorption density: Defines the density of absorption in 1/m units. The higher this density the higher the absorption. This option gives easy control to the magnitude of absorption and it is possible to set a procedural texture in order to define spatially varying absorption (heterogeneous medium)
  • Scatter color: Defines the scattering color ‐ this is the color that bounces off of particles (in the medium). The sum of absorption and scatter color (multiplied by their corresponding densities) defies the extinction coefficient of a medium which is used to calculate the total absorption at a distance. The scatter color may be applied numerous times for particles that bounce inside the medium (especially for highly scattering medium) and so, it is also recommended here to avoid highly saturated colors
  • Scatter density: Defines the density of scattering in 1/m units. The higher this density the higher the scattering. This option gives easy control to the magnitude of scattering and it is possible to set a procedural texture in order to define spatially varying scattering (heterogeneous medium)
  • Phase function: Defines the variation of outgoing radiance over the sphere of directions and it is the medium analog of a bi‐directional scattering distribution function (which is used for surface). The available functions are the Isotropic, Rayleigh, Mie Hazy, Mie Murky, Mie Retro or Henyey-Greenstein (you can also set the asymmetry value below it). Most used phase functions are Isotropic and Henyey‐Greenstein
  • Asymmetry: Defines the asymmetry parameter of Henyey‐Greenstein phase function. This parameter is unitless and takes values from –1 (totally back scattering) to 1 (totally front scattering). Obviously the extreme values of –1 and 1 do not actually scatter light outside the particle direction and they are not of practical use. A value of 0 is balanced scattering between back and forth directins and it is the same as using an isotropic phase function

Medium tab