# Sss#

(MaterialPhysicalSss)

• Category: /Material/Physical
• Default object name: sss

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## Description#

A sub-surface scattering physical material

## Attributes#

Name Type Description
Export Aovs bool Compute and write Aovs defined in the shading graph
Arbitrary Output Variables reference (AovStore) Set the list of extra channels to write to the image.
Light Path Expression Label string Set the material label in light path expressions.
Material Sample Count long Material sample count per pixel.
Subsurface Sampling Multiplier double Material subsurface sample count multiplier.
Russian Roulette double Amount of Russian roulette used on the material samples.
Roughness Noise Optimization double Noise reduction strategy along rough light path.
Diffuse Depth long Maximum diffuse depth.
Opacity double[3] Opacity of the material.
Normal Mode long Define which geometric normal to use for the shading.
Normal Input double Override the shading normal by the one given as input. The value controls the blending with the original normal.
Sidedness long Sidedness of this surface used for this material. 'Single' keeps the original normals no matter what. 'Double' may flip the normal to be oriented toward the incomming direction. 'Invert' flips the original normal no matter what.
Shadow Casting Mode long Defines the properties of the material when casting shadows: fully opaque (regardless of the actual value of the opacity of the material), artistic (user-defined opacity and coloring), pseudo-caustics (cheaply emulating actual refractive caustics) or physical (intrinsic transparency of the material), where the last three are modulated by the opacity of the material.
Shadow Opacity double Defines how dark the shadows cast by this material are.
Shadow Coloring double Defines how much refraction and absorption colors affect shadowing.
Subsurface Model long Technique used to simulate sub-surface scattering. A diffusion kernel cheaply approximates the aggregate light paths that reach the surface, and is a close match when the diffuse mean free path is smaller than the geometric features of the object onto which the material is applied. Instead, the random-walk scheme simulates actual scattering events inside the medium, which requires more computation and samples, but more accurately captures fine-scale illumination details.
Diffusion Model long Diffusion profile used to model the attenuation of light with distance due to subsurface scattering. The Gaussian profile is a blurry phenomenological model. The cubic profile is a sharper and more efficient approximation. The empirical profile is a good fit to actual SSS measurements.
Max Bounces long The maximum number of random-walk sub-surface bounces.
Subsurface Preset long Set of measured optical properties for several sample materials.
Optical Mode long Select how to specify the optical properties of the material. The volume mode is more physicist-friendly since it takes as input the intrinsic optical properties of the volume, and makes it possible for the user to copy-paste measured values from real-world materials (as may be found online and/or in the literature). The surface mode is more artist-friendly since it takes as input WYSIWYG-like parameters, and makes it possible for the user to eye-ball the expected overall appearance to quickly achieve a certain look. The hybrid mode is a mix of the volume and surface modes, and is mostly provided for backward-compatibility and portability purposes.
Volume Albedo double[3] Single-scattering albedo of the volume particles, i.e., the color of the individual particles that scatter light inside the volume.
Volume Mean Free Path double[3] Wavelength-dependent mean free path between individual extinction events in the volume, i.e., how far each color channel of a light beam penetrates on average into the volume before being absorbed or scattered by a particle.
Diffuse Albedo double[3] Average surface albedo resulting from all sub-surface scattering events inside the material.
Diffuse Albedo Gain double Scaling factor of all color channels of the diffuse albedo.
Diffuse Mean Free Path double[3] Wavelength-dependent diffuse mean free path traveled overall by light underneath the surface.
Mean Free Paths Scale double Scaling factor of the volume/diffuse mean free paths at all wavelengths.
Mean Free Paths Exponent double Base-ten exponent multiplying the volume/diffuse mean free paths at all wavelengths.
Anisotropy double The anistropy of the volumetric phase function. -1 is highly back-scattering, 0 is isotropic and 1 is highly forward-scattering.
Surface Transmission long The scattering function at the boundary of the subsurface layer.
Surface Color double[3] Color multiplier influencing the light coming from the front/back, can be seen as a very crude scattering term. Note that changing this value will break physical plausibility in the diffusion model. When path-traced subsurface is enabled, this value represents the surface color tint at the point the scattered ray intersects the surface.
Index Of Refraction double The refractive index of the subsurface layer.
Sss Group string Name of the group among which illumination propagates between SSS materials.