Hi everybody,

I would like to render my scene with ambient occlusion. AFAIK there are two options:

1. turn on Ambient Occlusion for every material
2. render a special Ambient Occlusion pass and then merge it with the “normal” rendering in Photoshop

I don’t like the option 1, because sometimes I just simply forget to turn AO in every material where it should be. Option 2 seems for me much better, but my question is, what if I have quite a lot of glass object in my scene? When I overwrite all materials in the render setup dialog for a special mental ray material just with AO, then of course all my glass objects are not transparent any more. And for example in the case of windows it is problem. I can turn off rendering of glass objects for the AO pass, but sometimes it is not so easy to find all glass objects in the scene.

So please what is the best workflow to have overall AO in a scene containing quite a lot of glass objects (windows, glass walls etc.)

Thank you very much for help.

3ds Max Design 2009
HP xw8600
2xIntel Xeon X5482
16GB RAM
Quadro FX 5800
SAS RAID 5

I don’t use max, but in Maya this is my worklow:
1. Turn on AO for all objects
2. Bake Ao to a file
3.  Open in PS and merge with the texture file
This way, I can render from any angle w/o having to redo the AO pass

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zbyss, I would definitely go with option 2.  Turning on AO in your materials can really slow down render times.  Creating an AO pass and compositing later gives you more control over how light or dark it is, and you can clean up areas where you don’t necessarily want to see it.

For glass, I try to put it all on a separate layer, then hide that layer when I render the AO pass.  If it’s an AEC window, it’s a little tougher.  But if it’s a small window, it may not impact the final image a lot if there is no AO beyond the glass.

One possible workaround is to select the window objects, go into properties, and make them not visible to camera for the AO pass.  It may not be perfect, but a little Photoshop work would fix it, I think.

3DS Max Design 2011 64-bit - Advantage Pack
Dell Precision T5500, Dual Six Core Xeon X5650 @ 2.67GHz, nVidia Quadro 5000, 24 GB RAM, Win 7 Enterprise 64-bit
Minneapolis, MN, USA

Thank you for your comments Chris, I just thought there would be some “smarter” way than to hide the glass objects. But I can live with that :)

3ds Max Design 2009
HP xw8600
2xIntel Xeon X5482
16GB RAM
Quadro FX 5800
SAS RAID 5

Some reading for you:-
http://mentalraytips.blogspot.com/2008/11/joy-of-little-ambience.html