Volume Coefficients¶
The Volume Coefficients node models three physical processes in a volume: Absorption, Scattering and Emission, represented by their coefficients. Typical usage is to plug in values from real-world measurements.
輸入¶
Absorption¶
- Coefficients
Probability density per color channel that light is absorbed per unit distance traveled in the medium. It is equivalent to \((1-\text{Color}) \times \text{Density}\) in Volume Absorption.
Scatter¶
- Coefficients
Probability density per color channel of an out-scattering event occurring per unit distance traveled in the medium. It is equivalent to \(\text{Color} \times \text{Density}\) in Volume Scatter.
- Anisotropy Henyey-Greenstein Draine
Controls the relative amount of backward and forward scattering.
- IOR Fournier-Forand
Refractive index of the scattering particles relative to water. Common ocean waters range between 1.0 and 1.2, while turbid waters with higher density of particles have higher IORs.
- Backscatter Fournier-Forand
Fraction of light that is scattered backwards. Most oceanic particles have backscatter values between 0.001 (e.g., very large phytoplankton) and 0.1 (e.g., very small mineral particles), pure water has a backscatter of 0.5. Values taken from Ocean Optics Web Book.
- Alpha Draine
Blending factor between Henyey-Greenstein (\(\alpha = 0\)) and Cornette & Shanks (\(\alpha = 1\)) phase functions.
- Diameter Mie
Diameter of the scattering particles in µm.
Note
Above inputs are the same in Volume Scatter.
Emission¶
- Coefficients
Emitted radiance per color channel that is added to a ray per unit distance. It is equivalent to \(\text{Color} \times \text{Strength}\) in Emission.
屬性¶
- Phase
Note
Same as Phase in Volume Scatter.
Volume scattering phase function.
- Henyey-Greenstein:
Simple and widely used phase function, useful for approximating scattering in biological tissues.
- Fournier-Forand:
Cycles Only Suitable for modeling the scattering of light in underwater environments.
- Draine:
Cycles Only Suitable for modeling the scattering of interstellar dust.
- Rayleigh:
Cycles Only Describes the scattering by particles with a size smaller than the wavelength of light, such as the scattering of sunlight in earth's atmosphere.
- Mie:
Cycles Only Describes the scattering by particles with a size larger than the wavelength of light, such as cloud and fog.