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Simulating light passing through translucent materials like skin, wax, leaves, and marble to make them glow from within.
When light hits opaque materials like metal, it bounces off the surface. But translucent materials like human skin, plant leaves, and candle wax allow light to penetrate, scatter around inside, and exit at a different point. This is subsurface scattering, and it is the reason ears glow red when backlit, why holding a flashlight against your hand makes your fingers glow, and why marble statues seem to have an inner warmth. In rendering, simulating SSS is essential for realistic skin because without it, characters look like they are made of plastic or painted porcelain. The effect adds a subtle warmth and translucency that our eyes expect from organic materials.
Example
The character models in The Last of Us Part II use sophisticated subsurface scattering for skin rendering, which is a major reason the characters look so lifelike in close-up cutscenes. When light hits Ellie's face from behind, you can see the warm glow through her ears and the thin skin around her nose. God of War Ragnarok applies SSS to Kratos's skin in ways that make harsh Nordic lighting look natural on his face. Even Fortnite's stylized characters use simplified SSS to keep skin looking organic rather than plastic.
Why it matters
Subsurface scattering is the difference between a character that looks alive and one that looks like a mannequin. As games push toward photorealistic humans in cutscenes and gameplay, SSS becomes non-negotiable. It is also critical for any game featuring natural environments, where leaves, fruit, and other organic materials need to interact with light convincingly.
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