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3D Why ambient occlusion in path tracing?

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Hello,

I am learning about path tracing and I have a doubt about ambient occlusion. Specifically, why do we need AO in path tracing? Path tracing with global illumination already shoots rays around the normal hemisphere to take diffuse/specular indirect light, direct light into account and naturally leads to soft shadows (where appropriate), so to me it seems like doing almost the same thing twice if we add AO in a path tracing context (AO does not even exist in the real world). I do understand how it is useful in rasterization though, where it can fake some soft shadows to increase perception of depth. 

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You most definitely don't need it in path tracing (for the reasons you mentioned), and I don't know of any path tracers that use it. 🙂

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with that said, may I ask the resource that incorporates ao for path tracing or is this a personal thought? My first thought was a speed optimization or ray killer but I'm a very dark shade of green on the topic.

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It's useful in realtime raytracing. GI samples are more expensive to compute per sample and need more samples to converge, AO is a nice hack for realtime whether your rasterizing or raytracing.

But for a traditional pathtracer I'm not sure why you'd want to use it. Maybe it's some artist control?

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Thanks a lot for the answers! That clears the doubt I was having. I got confused because Cycles for example, the path tracer used by Blender for 3D renders, does have an option to add ambient occlusion. 

Some more research confirmed that option is there merely for test / artist control purposes :)

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