What is Ambient Occlusion and Why Does It Matter?

Ambient occlusion (AO) is a shading technique that calculates how much ambient light reaches a given point on a surface. Areas that are open and exposed receive full ambient light. Areas that are tucked into corners, creases, or tight spaces receive less ambient light because surrounding geometry blocks it — they're occluded.

In the real world, this happens constantly. Look at the corner where two walls meet — it's always slightly darker than the middle of either wall, even in a brightly lit room. Look at where a mug sits on a desk — there's a subtle shadow ring at the contact point even without a direct light source causing it. That's ambient occlusion.

Ambient Occlusion — Where Light Gets Blocked

To calculate AO, the renderer casts a large number of rays from each point on a surface outward in a hemisphere shape. It then counts how many of those rays hit nearby geometry before escaping into open space. A point that has many rays blocked by nearby surfaces gets a dark AO value. A point with few blocked rays gets a bright value.

Imagine standing in the middle of a field — you can see the full sky in every direction. Now imagine standing in a narrow alley — most of the sky above you is blocked by the walls. The alley is naturally darker even in the absence of direct shadows. AO simulates this effect for every point on every surface.

The result is a grayscale map where the brightness of each pixel tells you how much ambient light that surface point receives. This map is the AO map — and it's one of the core textures in a PBR workflow.

An AO map is always a grayscale image. White pixels represent areas fully exposed to ambient light. Black pixels represent areas that are heavily occluded. The majority of a typical AO map is white or near-white — only corners, contact edges, and tight gaps go dark.

AO maps are almost always stored as a single channel (grayscale) image and exported as PNG. In many PBR pipelines, particularly when targeting Unity or Unreal, the AO map is packed into the green channel of a combined texture alongside Roughness and Metallic — this is called an ORM texture (Occlusion, Roughness, Metallic) and reduces the number of texture samples the GPU needs to perform.

There are two main ways to get AO into your scene. Understanding the difference helps you choose the right approach for your project.

For most game assets — props, characters, environment pieces — baked AO is the right choice. It costs nothing at runtime, looks great, and gives you full control over the result. Realtime AO methods like SSAO are typically added on top by the engine as a post-process effect for dynamic interactions.

Once you have a baked AO map, plugging it into your material is straightforward in every major engine. The AO map is always multiplied against the base color — it darkens areas that are occluded without affecting the hue of the surface color.

A common technique is to also multiply your AO map against the Albedo (color) map before plugging it in. This bakes the AO darkening directly into the color channel, giving you more control over how strongly the occlusion affects the final look regardless of engine-specific AO settings.

Trumble's Bake tool generates an AO map directly from your mesh geometry in the browser. The baker casts rays from the surface of your low-poly mesh and records how much of the hemisphere is blocked by the mesh itself or any cage geometry you define. The result is exported as a grayscale PNG ready to import into Unity, Unreal, Godot, or any other engine.

A few settings that matter when baking AO in Trumble: