What Is Subsurface Scattering?

Definition: Subsurface Scattering

Subsurface scattering (SSS) is a phenomenon in which light penetrates the surface of a translucent object, scatters inside the material, and exits at a different point. This effect is crucial for rendering realistic materials like human skin, wax, marble, and liquids in computer graphics and visual effects.

Understanding Subsurface Scattering

In real-world materials, light doesn’t always reflect directly off surfaces. Instead, it enters the material, bounces around, and diffuses before exiting. This behavior is essential for rendering lifelike organic materials such as skin, milk, jade, wax, and clouds. Without subsurface scattering, these materials would look unnaturally opaque and plasticky.

In computer graphics, CGI, and ray tracing, subsurface scattering is simulated to enhance realism. Render engines like Blender’s Cycles, Unreal Engine, Arnold, and V-Ray use specialized algorithms to calculate light diffusion inside materials.

How Subsurface Scattering Works

The process of subsurface scattering involves several key steps:

1. Light Enters the Surface – When light hits a translucent object, some of it penetrates the surface instead of bouncing off.
2. Internal Scattering – The light bounces inside the material, interacting with its microscopic structure.
3. Exit Point Diffusion – After scattering, the light exits at a different location on the surface, creating a soft, glowing effect.

The scattering distance and color absorption properties determine how far and in what way light spreads inside the material. For example, human skin has different layers where light scatters, contributing to its soft and warm appearance.

The Importance of Subsurface Scattering in Computer Graphics

1. Realistic Skin Rendering

Subsurface scattering is a key element in rendering human skin in movies, video games, and digital art. Without SSS, skin would look flat and artificial. Realistic skin rendering involves simulating how light interacts with epidermis, dermis, and subcutaneous fat layers.

2. Photorealistic Material Creation

Many everyday objects, like marble statues, wax candles, fruit, and leaves, rely on SSS to appear natural. A lack of subsurface scattering makes these materials look dull and unrealistic.

3. Enhanced Lighting in CGI and VFX

Modern render engines use SSS shaders to simulate complex light behavior, making CGI elements blend seamlessly with real-world footage in movies and advertisements.

4. Improved Visual Realism in Games

Game engines like Unreal Engine and Unity incorporate subsurface scattering for characters, helping them look more natural under different lighting conditions.

Common Uses of Subsurface Scattering

• Film & Animation – Pixar and Disney use SSS in 3D characters to achieve lifelike animation.
• Video Games – High-quality game graphics use SSS for realistic character models.
• Medical Visualization – SSS helps simulate human tissue in medical imaging software.
• Product Design – Materials like plastic and rubber use SSS to improve realism in product renderings.

How to Implement Subsurface Scattering in 3D Rendering

1. Use a Subsurface Scattering Shader

Most modern rendering engines provide built-in SSS shaders. Examples include:

• Blender – Principled BSDF shader with SSS settings.
• Maya (Arnold Renderer) – Subsurface scattering material nodes.
• Unreal Engine – Subsurface Profile shader for realistic skin.

2. Adjust Subsurface Color and Radius

• Subsurface Color – Determines the internal scattering color (e.g., red tones for skin).
• Scattering Radius – Controls how far light spreads inside the material.

3. Balance Translucency and Opacity

For best results, fine-tune translucency settings to balance between solid and translucent appearances.

4. Use High-Quality Textures

High-resolution normal maps, roughness maps, and albedo textures help enhance the final look when combined with subsurface scattering.

Frequently Asked Questions Related to Subsurface Scattering