Layer types

You may find more information on the layer properties mentioned here in the Layer properties page.

COATING LAYER

The coating layer uses a special reflection model with only the specular component. It is useful for simulating varnishes and paints on a layered material. You can use several coating layers to simulate multiple varnishes and paints. The coating itself reflects some light, while any layers of material underneath absorb the rest of the light. You can change the extinction coefficient to modify the reflectance (based on Fresnel equations) and define the absorption density of the layers of material underneath. Both the extinction coefficient and the thickness of the layered material are used to calculate absorption at a microscopic level.

Material editor: Coating layer on top of basic No coating With coating

The basic properties of the coating layer are the following:

  • Reflectance
  • Linear roughness
  • Bump

The following properties are hidden by default and can be accessed by clicking on the hamburger icon:

  • Index of Refraction (N)
  • Extinction coefficient (K)
  • Thickness / Absorption map
  • Anisotropy
  • Rotation (deg)
  • Micro roughness
  • Random glints

Example: Thickness / Absorption map
Thickness refers to the thickness of the coating layer. This option can be used to simulate special coatings found in car paints. In the following images we have applied two different materials to the same objects.

Basic layer only. Orange color in the diffuse channel Basic + Coating: Coating absorption set to orange


BASIC LAYER

The basic layer consists of a diffuse, translucent, and Fresnel based specular component. It is a highly energy efficient material designed to be used mostly for matte and plastic materials. You might also use basic layers to create metals and translucent materials. Metals, in most cases, have a non‐zero extinction coefficient, which corresponds to a high Fresnel coefficient under any viewing angle.

Material editor: Basic layer Basic layer with reflectance

The basic properties of the coating layer are the following:

  • Diffuse
  • Reflectance
  • Roughness
  • Bump

The following properties are hidden by default and can be accessed by clicking on the hamburger icon:

  • Index of refraction (N)
  • Extinction coefficient (K)
  • Translucent
  • Absorption (1/m)
  • Anisotropy
  • Rotation
  • Micro roughness
  • Random glints

Example: Translucency / Absorption
The difference in using translucency and translucency + absorption.

No translucency. No absorption Translucency set to orange color Translucency set to white. Absorption set to orange and a value of 50


METAL LAYER

You can create a metal with perfect reflection (roughness = 0), a very rough metal (roughness = 100), or something in between. The Bidirectional Scattering Distribution Function (BSDF) uses Fresnel equations for reflections, which is controlled by the index of refraction and the extinction coefficient. Set the index of refraction to around 1 to make the material less reflective. As you increase the value, reflection becomes stronger and stronger; at very high values, the reflected light takes on the color of the selected color. Use a non‐zero value for the extinction coefficient to amplify reflection.

Material editor: Metal layer Metal layer


GLASS LAYER

You can create a glass with perfect reflection and refraction (roughness = 0), a very rough glass (roughness = 100), or something in between. The Bidirectional Scattering Distributi􀀵on Function (BSDF) uses Fresnel equations to balance reflection and refraction, which is controlled by the index of refraction and the extinction coefficient. Set the index of refraction to around 1 to make the material less reflective and more refractive. Set the value to exactly 1 to make the glass perfectly transparent. As you increase the value, reflection becomes stronger and stronger; at very high values, the reflected light takes on the color of the selected color.

Material editor: Glass layer Glass layer

The basic properties of the coating layer are the following:

  • Transmittance / Absorption color (Transmittance changes to absorption color when the absorption value is greater than 0)
  • Absorption (1/m)
  • Roughness
  • Bump

The following properties are hidden by default and can be accessed by clicking on the hamburger icon:

  • IOR file
  • Index of refraction (N)
  • Extinction coefficient (K)
  • Reflectance
  • Abbe number
  • Anisotropy
  • Rotation
  • Micro roughness
  • Random glints

Example: Transmittance vs absorption

Transmittance Absorption

Example: Abbe number

Abbe number disabled Abbe number enabled


THIN GLASS LAYER

This glass model describes thin glass materials that show perfect (mirror) reflection and transparency. Thin Glass models are very accurate models and are great for assigning to thin surfaces, such as windows and thin transparent plastics. Although you could also use a glass material with transmittance enabled and index of refraction set to 1, it is recommended to use the glass model whenever you want to achieve transparency. Another way to achieve transparency is to actually model a surface, such as a window, as a thin double interface where refraction takes place at both sides. Using the glass model though is optimal in terms of visual accuracy and additionally, it can be traced during shadow evaluation (something like this cannot be done with the double interface model which will create shadows). The glass model does not assume the model to be closed as it does not define an interior/exterior volume. The index of refraction is used as if the model was a double interface, in order to compute the overall transmittance due to double refraction.

Material editor: Thin Glass Thin Glass layer

The basic properties of the coating layer are the following:

  • Transmittance
  • Bump

The following properties are hidden by default and can be accessed by clicking on the hamburger icon:

  • Index of refraction (N)
  • Interference
  • Thickness

Example: Interference

Interference: Thickness set to 500 Interference: Thickness set to 450 Interference: Thickness set to 410


SSS LAYER

The Bidirectional Subsurface Scattering Distribution Function (BSSDF) is a generalization of the Bidirectional Scattering Distribution Function (BSDF); however, unlike BSDF, the entry and exit points for BSSDF may differ instead of coinciding. Therefore the evaluation of BSSDF is far more difficult, as it involves the interaction of surface reflectance / transmittance along with scattering through participating media. Besides the surface reflectance entries, there are also parameters describing absorption and scattering inside the object. In order for the SSS material to be evaluated correctly, the object should be closed (without holes). Participating media with high albedo (i.e., when the scatter density is much higher than the absorption density) are particularly difficult to render. To accelerate rendering with minimum loss of accuracy, usually you can turn an asymmetric medium into an anisotropic medium with a synchronous decrease of its scatter density. Assuming that the asymmetry of the medium is g > 0, you can set asymmetry to the isotropic value of 0 and decrease the scatter density to a value that is equal to the old scatter density multiplied by 1‐g. The new medium will have lower albedo, and it will render faster with minimum loss of accuracy.

Material editor: SSS layer SSS layer

The basic properties of the coating layer are the following:

  • Absorption (1/m)
  • Scattering
  • Reflectance
  • Roughness
  • Bump

The following properties are hidden by default and can be accessed by clicking on the hamburger icon:

  • Index of refraction (N)
  • Asymmetry
  • Anisotropy
  • Rotation
  • Micro roughness
  • Random glints

Example: Asymmetry

T4R_SSS_Asymmetry