Ambient Occlusion Pass for interior scenes

There are several ways to render out an ambient occlusion (AO) pass in max with mental ray. However some AO setups require environment changes, and don’t always work with interior scenes. I will explain how to get an AO pass that always works. For those of you who don't know what AO is, it's a method of creating soft shadows in corners where objects meet. It adds an extra sense of reality.

Ambient Occlusion Pass for interior without windows

Create a new mental ray shader. Insert the Ambient/Reflective Occlusion map into the diffuse slot, and put a value in the max distance of the AO map.













In your render settings under the Processing tab turn on Material Override and just click and drag the AO material into the blank material slot under Material Override. Now all of your materials in your scene will use this AO material, even though they still have their own shaders applied to them. Before you render, turn off FG, GI and turn off your exposure. If you don't do this you will get a black rendering. All of these settings will not be lost.

straight render pass before AO is added

Final composite of AO and beauty pass combined

The nice thing about this process is you don't have to turn off or delete any lights in the scene, and you still keep all of your materials intact. When you are done rendering the AO pass just turn back on FG, GI, and your exposure...all of your settings will still remain. Also don't forget to disable the Override Material before you go back to rendering your beauty pass.