Medium

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

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 toward white. When the distance gets bigger, the transmittance shifts toward black. The color change with distance is strongly non-linear; thus, it is recommended to avoid highly saturated colors.

Absorption density: Defines the density of absorption in 1/m units. The higher the value, the higher the absorption. You can select 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, defines 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 a highly scattering medium); thus, it is recommended to avoid highly saturated colors.

Scatter density: Defines the density of scattering in 1/m units. The higher the value, the higher the scattering. You can select 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. The phase function is the medium analog of a bidirectional scattering distribution function (which is used for surfaces). The available functions are isotropic, Rayleigh, Mie Hazy, Mie Murky, Mie Retro and 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 the Henyey-Greenstein phase function. This parameter is unit-less and takes values from –1 (totally back scattering) to 1 (totally front scattering). 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 directions and it is the same as using an isotropic phase function.