Ambient Occlusion
Soft contact shadows
Also known as: AO · AO map
Definition
Ambient occlusion (AO) is a shading effect that darkens recessed crevices and contact points where ambient light would naturally have a harder time reaching. As a texture channel it is baked from the high-poly mesh and used to subtly tint the albedo and roughness, grounding the model visually. Real-time engines also compute screen-space AO (SSAO) at runtime to add contact shadows that a static map cannot capture.
In production
Bake AO from the high-poly model in Marmoset Toolbag or Substance Painter, then multiply it into the albedo and/or pack it into a separate ORM texture channel for engine consumption. Bake settings matter: ray count and max occlusion distance (often called "spread" or "search radius") need tuning per-asset, since too large a distance darkens broad convex surfaces that should stay bright, while too small a distance misses occlusion in deep recesses like engraved panel lines. A well-known pitfall is baking AO with the low-poly's own geometry as the occluder instead of the high-poly — this produces faceted, blocky shadows that don't match the sculpted detail. In Unreal Engine 5, baked AO is typically packed into the ORM texture's red channel and combined at runtime with Lumen's dynamic global illumination and screen-space AO, so an overly dark static bake can double up with real-time occlusion and crush shadow detail to pure black. Most studios cap static AO's contribution (an "AO intensity" slider in the material) to avoid this stacking artifact.
