Autodesk Standard Surface#
The Autodesk Standard Surface is a multipurpose physical material compatible with the Autodesk Standard Surface Material (ASSM) specification. This material which is already available in Autodesk Arnold, allows you to accurately mimic most real world materials like plastics, metals, liquids, fabric, glass or skin from a reduced set of parameters as seen in the illustration above.
For more information about ASSM, please refer here.
Note
All the renders in this page are rendered with Caustic Sharpness to 100%
The image below uses a Autodesk Standard Surface material on the sphere with default settings:
Important
The Autodesk Standard Surface material doesn't guaranty a 100% look consistency across the different rendering engines implementing it. While you can expect to get extremely close results, some features such as multiple scattering or subsurface scattering are likely have different implementations leading to subtle render differences.
Base#
The Base set of attributes controls the base layer of the material. It is defined by a Oren-Nayar diffuse reflection mixed with a GGX conductor. The blending between the two models is controlled using Metalness attribute which defines the metallic property of the material. The final color of the base layer is defined by Base Color which is then multiplied by Base Weight.
| Attribute | Description |
|---|---|
| Base Weight | Set the intensity of the base layer. |
| Base Color | Set base diffuse and reflection color. |
| Diffuse Roughness | Set the roughness of the diffuse layer. |
| Metalness | Set the metalness property of the material where a value of 0.0 is a pure dielectric (glass, plastic, leather...) and 1.0 a metal conductor (copper, gold, silver). |
Diffuse Roughness#
- Diffuse Roughness defines the roughness of the diffuse layer. The diffuse BRDF is an Oren-Nayar where a roughness of 0.0 corresponds to a pure Lambertian surface and high roughness values mimic rough surface such as concrete or sand.
Metalness#
Metalness defines how metallic the material is. A non metallic material (defined by a Metalness of 0.0) behaves like pure dielectrics such as glass, plastic, leather... Pure metallic materials on the other hand are defined by a Metalness of 1.0 in which case react like metal conductors such as copper, gold, or silver...
Any in-between values simulate hybrid materials that are a mix of dielectric and conductor. Such materials are quite common in real world like you can find on base coat of metallic car paints, that are a mix of a solid paint (reacting like a dielectric material) and metal flakes (conductors).
Specular#
The Specular set of attribute controls the properties of the conductor/metallic layer.
| Attribute | Description |
|---|---|
| Specular Weight | Set the intensity of the reflection. |
| Specular Color | Set the reflection color. When the material is fully metallic Specular Color only tints the reflection at glancing angles |
| Specular Roughness | Set the roughness of the reflection. |
| Specular IOR | Set the index of refraction of the dielectric material. This attribute is completely ignored when the material is fully metallic. |
| Specular Anisotropy | Set the anisotropy of the reflection |
| Specular Rotation | Set the direction of the anisotropy |
Specular Color#
The Specular Color attribute allows you to tint reflection by the specified color. The actual resulting color of the reflection is multiplication between Base Color, Specular Color and Specular Weight.
When the material is metallic (Metalness set to 100%), Specular Color only tints reflections at glancing angles.
For example, the 2 renders below are both set with a blue specular color. If you switch between the two renders, note that on the material that has its Metalness set to 100%, only the glancing angle of the sphere gets tinted in blue.
Specular Roughness#
Specular Roughness defines the roughness of the metallic layer. The rougher the surface is, the softer the specular reflection. Perfect mirrors should have a roughness of 0% and perfectly rough (diffuse) surface should have a roughness of 100%.
Specular IOR#
Specular IOR defines index of refraction of the dielectric which controls intensity of the reflection according to the fresnel. Please note that Specular IOR has absolutely no effect when the material is fully metallic (Metalness set to 100%).
Specular Anisotropy and Rotation#
Specular Anisotropy and Specular Rotation allow you to simulate brushed materials. Specular Anisotropy controls how much the specular highlight is stretched along the axis and Specular Rotation specifies the major direction of microfacets (0% gives no direction, 50% gives 90° rotation and 100% gives 180° rotation). Specular Rotation expects a black and white texture that defines the direction of the anisotropy.
Tip
It is highly recommended to disable image filtering (setting it to Nearest Neighbor) when using texture maps to control Rotation to avoid any interpolation artifacts.
Note
The axis of the anisotropy is controlled by the first UV of the geometry when available. When no UV is available the anisotropy uses a local axis which doesn't guaranty continuity. For best results it is recommended to use a UV map with as few discontinuities (seams) as possible.
Transmission#
The Transmission set of attribute controls how transmissive the material is. The roughness and index of refraction of the transmission are both linked to Specular Roughness and IOR respectively. It is however possible to add or remove extra roughness to the transmission using Transmission Extra Roughness attribute.
| Attribute | Description |
|---|---|
| Transmission Weight | Set the intensity of the transmission. |
| Transmission Color | Set the transmission color. |
| Transmittance Depth | Set the transmittance depth. |
| Transmission Scatter | Set the scattering color within the inner volume. |
| Transmission Scatter Anisotropy | Control the anisotropy of the medium scattering. |
| Transmission Extra Roughness | Set positive or negative extra roughness for the transmission. |
Transmission Weight#
It is possible to add transmissive property to the material by using the Transmission Weight attribute. Please note that the Autodesk Standard Surface does not provide a physically correct dielectric material when it is both reflective and refractive.
Transmission Color#
The Transmission Color attribute defines the color of the transmission multiplied by Transmission Weight.
Transmittance Depth#
The Transmittance Depth (measured in scene units) simulates the density of the dielectric medium to filter the color of ray the further it travels through the material.
The depth directly translates into the scale factor on which the ray is attenuated. The higher the value, the less dense the volume and the more the color of the ray shifts towards the color defined by Transmission Color because less absorption and scattering occurs.
Transmission Scatter#
The Transmission Scatter attribute defines the inner medium scattering which is very useful to simulate semi translucent frosted ice for example.
Enabling transmission scattering is very computationally expensive especially that it may need a lot of bounces and the activation of caustics to be physically accurate.
The maximum number of bounces of the transmission scattering is controlled by the Volume Depth attribute.
Transmission Scatter Anisotropy#
The Transmission Scatter Anisotropy attribute controls the anisotropy of the medium scattering. By default, it is set to 0 so that light is scattered isotropically by the same quantity in all directions.
Positive values bias the scattering forward in the direction of the light while negative ones backward toward the light.
Transmission Extra Roughness#
The Transmission Extra Roughness attribute is an artistic control that allows you to add or remove roughness to the value defined by Specular Roughness. This is very useful to unlink the roughness value of the refraction from the reflection. Please note that final transmission roughness value is always normalized (between 0 and 1).
The renders below all have a Specular Roughness set to 0.0%
The renders below all have a Specular Roughness set to 25.0%
Subsurface#
The Subsurface set of attributes simulates the effect of light penetrating a translucent surface that is scattered multiple times inside before exiting the surface. It is used to simulate the translucency component of wax, skin, marble etc... The material approximates a homogeneous volume on which properties are defined from the entry point and the subsurface parameters.
Note
Fully transmissive materials can't define a subsurface layer.
| Attribute | Description |
|---|---|
| Subsurface Mode | Set the engine used to simulate subsurface scattering. |
| Subsurface Weight | Set the weight of the subsurface. |
| Subsurface Color | Set the color of the subsurface. |
| Subsurface Radius | Set the radius of the subsurface. The bigger the value, the more light penetrates the medium. |
| Subsurface Scale | Scale applied to Subsurface Radius. |
| Subsurface Anisotropy | Set the anisotropy of the medium scattering. |
| Subsurface Group | Set a surface group The Subsurface Group attribute enables the user to specify the name of a group among which illumination propagates between materials with subsurface. |
Subsurface Mode#
The Subsurface Mode attribute allows you to choose between two techniques to approximate subsurface scattering:
| Model | Description |
|---|---|
| Diffusion | Diffusion aggregates light paths around the entry point of the surface and integrate their contribution. Diffusion is an efficient technique which works really well when mean free path is smaller than the geometric details of the geometry. This technique is faster to render than Random Walk. |
| Random Walk | Random Walk path traces light paths inside the surface making it a better approximation for thin surfaces which is more expensive and slower to compute than Diffusion. Random Walk approximates more accurately the scattering inside the medium and captures more realistic fine geometric details of the geometry that are missed by the Diffusion. Since it requires more samples, it is also more expensive and slower to compute than Diffusion. |
In the render below, the Subsurface Scale is larger than the fine geometric details of the model. As you can see, Diffusion fails to capture the illumination compared to Random Walk:
If we increase the Subsurface Scale, the difference between the two methods becomes even more pronounced:
Translucency#
Both Diffusion and Random Walk make the assumption that the underlying geometry defines an enclosed volume. If the geometry isn't defining an enclosed volume (such as how leaves and grass blades are usually modeled) you must enable the Thin Walled attribute so that SSS works properly since enabling Thin Walled falls back to an alternate method using diffuse transmission, simulating translucency, which is well suited for such geometries.
In the render above, Thin Walled has been enabled to simulate a translucent sheet of paper made of a single polygon.
Subsurface Color#
The Subsurface Color attribute defines the color of the subsurface scattering reflected from below surface.
Subsurface Radius#
Subsurface Radius defines the maximum distance light can penetrate and scatter below the surface defined as a color. This attribute actually defines the average distance of each wavelength (RGB) for which light can be absorbed and scattered by the medium. Increasing this value directly impacts the translucency of the material. This attribute internally defines the Mean Free Path (MFP) which corresponds to the average distance light can traveling through the surface before exiting.
Subsurface Scale#
The Subsurface Scale is simply a scale multiplying the Subsurface Radius. In the render below, we are using the Chicken 1 preset with different value of Subsurface Scale:
Tip
It is highly recommended to set Subsurface Mode to Random Walk when Subsurface Radius is larger than the thickness of the geometry since Diffusion sampling technique is going to fail capturing geometric details that are smaller than the subsurface radius.
Subsurface Anisotropy#
The Subsurface Anisotropy attribute controls the anisotropy of the medium scattering. By default, light is scattered isotropically (by the same quantity in all directions). Positive Anisotropy values bias the scattering forward in the direction of the light while negative ones backward toward the light.
Tip
It is recommended to use the Random Walk technique when specifying positive values of anisotropy since it will lead to a loss of energy using Diffusion.
Coat#
The Coat set of attributes allows you to define a thin dielectric layer on top of all other layers to simulate clear coat.
| Attribute | Description |
|---|---|
| Coat Weight | Set the weight of the coat layer |
| Coat Color | Set the color of the coat. |
| Coat Roughness | Set the roughness of the coat. |
| Coat Ior | Set the index of refraction of the coat. |
| Coat Anisotropy | Set the anisotropy of the coat. Coat Anisotropy works the same way as Specular Anisotropy |
| Coat Rotation | Set the anisotropy rotation of the coat. Coat Rotation works the same way as Specular Rotation |
| Coat Normal | Set the normal of the coat layer. |
Coat Color#
The Coat Color defines the color of the coat layer. Please note that specified color is filtered before being transmitted to the layers below. If you specify a pure red coat color while the layer below is blue, the material won't be able to reflect blue since only red is transmitted below.
Coat Roughness#
The Coat Roughness allows you to specify the roughness of the coat independently from the base surface.
Coat Ior#
The Coat Ior allows you to specify an index of refraction for the coat independently from the base surface.
Coat Normal#
The Coat Normal allows you to specify a surface normal for the coat independently from the base surface. This is very useful to simulate scratches, water drops or a very glossy clear coat layer on top of a very rough material.
Sheen#
The Sheen set of attributes allows you to simulate an energy conservative layer made of microfibers such fabric, velvet, peach fuzz...
| Attribute | Description |
|---|---|
| Sheen Weight | Set the weight of the sheen. |
| Sheen Color | Set the color of the sheen. |
| Sheen Roughness | Set the roughness of the sheen which randomizes the direction of the microfibers. |
Emission#
The Emission set of attributes allows you to define the emissive property of the material to simulate incandescence.
| Attribute | Description |
|---|---|
| Emission Weight | Set the weight of the emission. |
| Emission Color | Set the color of the emission. |
Thin Film#
The Thin Film set of attributes simulates the effect of thin film interference occurring on some surfaces such as soap bubbles, oil puddles, coated lens/glass, insect wings etc...
| Attribute | Description |
|---|---|
| Thin Film Thickness | Set the thickness of the thin film layer in nm (nanometers). |
| Thin Film Ior | Set the index of refraction of the thin film medium. |
Thin Film Thickness#
Thin Film Ior#
Material Presets#
The material comes with many different presets mimicking a wide variety of real world materials that can be used as starting point for the lookdev. To choose one of the material presets just click on Material Presets and choose the material you want from the list.
Please note all translucent materials (such as wax, orange juice, skin) directly depends on the scale of the geometry. Most of the presets scale are defined in cm.
