tB

MAYA

Manual Ambient Occlusion Render Layer

Right mouse click (RMC) on the render layer you want to convert to AO layer.
Go to Override and create a new material override and make it a surface shader.
This should then open up the Attribute Editor for that new surface shader. Give it a name, “AO_mtrl” for example.
On the Out Color map button, select the Mental Ray “Mib_amb_occlusion” node under the Textures category.
This should then open up the Attr window for that node, make the “Max Distance” equal to 4 and you’ll have the basic AO settings. Remember to set the camera environment to WHITE because you’re going to ignore alpha when comping and you need a white bg. Use the “multiply” transfer mode.