Ambient Occlusion
Ambient Occlusion (AO) is a rendering technique that enhances scene realism by simulating how objects block ambient light in crevices, recesses, and contact areas, making the scene look more grounded and natural.
Parameters Overview
| Parameter | Description |
|---|---|
| Enable | Toggle to enable or disable Ambient Occlusion |
| Quality | Controls the quality of AO. Lower quality improves performance, higher quality gives finer detail but costs more performance |
| Intensity | Controls the overall strength of AO; higher values make AO more pronounced |
| Power | Adjusts the contrast of AO shadows; higher values make dark areas darker |
| Radius | Controls the spread range of AO, in meters. Larger radius makes occlusion spread farther. Range: 0.1 m – 10 m |
| Bias | Prevents self-occlusion artifacts, avoids surfaces darkening themselves. In meters. Range: 0 – 0.5 m |
| Bilateral Threshold | Removes noise without blurring object edges. Higher values make AO smoother |
| Min Horizon Angle | Ignores small angle occlusion to reduce artifacts |
Parameter Details
Radius
Global range, determines how far AO can spread
- Controls the sampling range of AO.
- Too small → AO only appears in narrow contact areas, looking “stuck to the edge.”
- Too large → AO spreads into areas that shouldn’t be darkened.
Bias
Local adjustment, only affects the relation between the pixel itself and its sample points
- Typically a very small positive number (recommended
0.001 – 0.01). - Adjusts the starting point of occlusion calculation to prevent a pixel from occluding itself.
- Too small → surfaces may darken themselves.
- Too large → valid occlusion may be ignored, making the image too clean.
- If the image looks too dirty → increase Bias.
- If occlusion looks too weak → decrease Bias.
Bilateral Threshold
- Blurs the AO texture to remove noise, but only within the same object surface while preserving edge sharpness.
- Higher values → AO becomes smoother and softer while keeping edges clear.
- Lower values → AO may contain noise or banding artifacts.
Min Horizon Angle
- Range:
0° – 45° - Think of it as the “minimum angle required to start calculating occlusion.”
- Near
0°: even tiny gaps are considered occluded. - At
45°: only more obvious recesses are considered.
- Near
Demonstration from 0° – 45°:
Using Ambient Occlusion
- In the Scene settings, locate Ambient Occlusion.
- Click Enable.
- Effect Comparison
AO Disabled
AO Enabled
Best Practices
-
Why does AO look too dirty?
- Don’t set the radius too high.
- Large radius + high intensity = dirty.
- Moderate radius + Bilateral Blur = natural.
-
Combine with other post-processing
- Use with Bloom and Tonemapping to make AO blend more naturally into the final image.
Limitations
Ambient Occlusion relies on the depth buffer, so it has the following limitations:
- No support for transparent objects: Transparent materials do not write to the depth buffer, so AO cannot be applied correctly to transparent surfaces.