Subsurface scattering explained

As 3D artists, we always strive for the perfect render. Understanding the way that light interacts with objects is critical for achieving photorealism. While some objects reflect most of the light, others absorb it and then let it pass through at different points, in a concept called subsurface scattering (SSS). In this article, we’ll explore the ins and outs of subsurface scattering and learn how it can be used in V-Ray to create realistic renders. 

Using Volumetric Scattering (VRayMtl) 

Jade/Marble Dragon

1. Apply a standard VRay material to the object. 
2. You could give it a little bit of reflectivity by setting the reflection color to mid-gray. 
3. Enabling refractions is an important step in enabling the VRay material's translucency capabilities. So, let’s set the refraction color to white.
4. Next, we need to choose the translucency type. Let’s go for volumetric.
5. By playing with the fog color and the depth, we can adjust the overall color of the material and its softness. Using the scatter color, we can set the color of the scatter.

Using VRayFastSSS2 

Candles

1. Apply VRayFastSSS2 to your object—ideal for skin, wax, marble, and other organic materials.
2. To create a wax material, we could play with the subsurface color and the scatter color. For example, we could set the sub-surface color to a yellow color, which is going to be the main color of the candle. And set the scatter color to orange, which is going to be visible in the thin parts of the candle geometry. This way, in the area around the flame of the candle, it’ll look more orange.
3. Next, we can play with the scatter radius parameter. In the case of wax, it is a good idea to allow the light to scatter deeper beneath the surface, so 2 cm should suffice. 
4. Finally, for creating a material such as wax, we need more of a forward scattering approach, so let’s set the phase function to account for that to 0.8.

Using VrayAlSurface  

Woman closeup

1. Apply VRayAlSurface to your object—this shader is versatile and designed for realistic skin and layered materials.
2. Set the diffuse color for the overall look of the material. It could be a flat color or a texture map. In this example, a texture map was used.
3. Make sure you enable subsurface scattering by setting the “SSS mix” parameter to 1.0
4. You could experiment with the parameters and colors of the three SSS layers to achieve the type of skin you’re after. The default values are getting pretty decent results too.
5. If you have a normal or bump texture, you could also plug it in to give your material an extra level of detail.
6. Finally, you could adjust the reflectivity of the material by playing with the reflection color and roughness parameter.

Using VRayFastSSS2

Forward/Backward/Isotropic Scattering

1. Apply VRayFastSSS2 to your object—ideal for skin, wax, marble, and other organic materials.
2. Set an overall color or texture that would serve as a base color.
3. You could play with the scatter color to adjust the subsurface scattering color of the material. It is mostly visible in the thin parts of the geometry. (Ears of a character, for instance).
4. By adjusting the scatter radius parameter, you can control the depth of scattering light inside the material. 
5. Finally, you can switch between several types of scattering using the phase function parameter. If the phase function parameter is set to ,0 that is called isotropic scattering. It means that light scatters uniformly in all directions (see example in image 01). A value of -1.0 would trigger backward scattering. In this condition, most of the light bounces back to the direction it came from (see example in image02). And finally, a value of 1.0 would trigger forward scattering. In this condition, the light scatters predominantly forward (see example in image 03).

Using VRayScatterVolume  

Icy sphere

1. The VRayScatterVolume material is designed solely as a brute-force option for SSS to produce an unbiased result. When used as a base material in a VRayBlendMtl, it can create complex materials with a subsurface scattering base. For example, we could create an ice material using the VRayScatterVolume.
2. We need to set an overall color to serve as a base. We could choose light blue.
3. Next, we can experiment with the sub-surface and scatter color until we get the result we’re after.
4. We should also experiment with the scatter radius parameter to control how deeply the light scatters under the surface.
5. Finally, we can adjust the phase function parameter. To create ice, we could set the phase function parameter to 0.15 to slightly favor forward scattering.

Using VRay2SidedMtl

Autumn leaves

1. The VRay2SidedMtl material is designed solely as a brute-force option for SSS to produce an unbiased result. When used as a base material in a VRayBlendMtl, it can create complex materials with a subsurface scattering base. For example, we could create an ice material using the VRayScatterVolume.
2. We need to set an overall color to serve as a base. We could choose light blue.
3. Next, we can experiment with the sub-surface and scatter color until we get the result we’re after.
4. We should also experiment with the scatter radius parameter to control how deeply the light scatters under the surface.
5. Finally, we can adjust the phase function parameter. To create ice, we could set the phase function parameter to 0.15 to slightly favor forward scattering.

Practical applications and case studies

Digital portraiture and character design

An excellent example of SSS in action is the way backlit ears appear to glow in their thinner areas, revealing how light penetrates and scatters through these regions. Due to its ability to produce a remarkable level of realism, SSS often proves to be an invaluable technique for creating more detail in lifelike skin textures in digital portraiture and character design.

Challenges and optimization strategies

It’s important to remember that SSS may appear a bit off due to issues such as overlapping faces, solid objects that are not closed (holes, unwelded vertices), lack of thickness, and incorrect scaling. To prevent this from happening, try not to rush when working on a project. Ensure your geometry is clean by taking regular breaks, being observant, and fixing any object irregularities you spot.

To wrap it up

Substance scattering is an excellent tool for adding an extra level of photorealism to your renders. It takes into account the physical properties of light and the way it interacts with each unique object, preventing them from looking plastic-like and creating a realistic representation of the scene’s surroundings. We encourage you to experiment and play around with the different shaders in V-Ray and explore which ones incorporate best into your workflow.

FAQs

Should I use subsurface scattering? 

You should definitely use SSS, especially for translucent objects. It can help make a huge difference in creating realistic skin, wax, marble, liquids, foliage, and more.

What objects have subsurface scattering? 

Any semi-translucent material where scattered light diffuses inside — skin, wax, marble and jade, fruits, milk, juice, leaves are just some examples.

How can I improve my renders using subsurface scattering? 

Use SSS for the right materials, and experiment with different shaders to see which one gets it just right. 

Does enabling subsurface scattering increase render time? 

Yes, but if used smartly, not by much. You can manage performance by using it selectively, and keeping in mind it’s a trade-off between time and quality.

Why is subsurface scattering important for 3D artists? 

SSS mimics how light interacts with real-world materials through scattering. Without SSS, materials lack depth and look artificial — skin looks plastic, wax looks flat, and characters, close-ups, and product shots lack photorealism.