How to optimize occlusion pass render?

[Ultrasonic]

Hi,

have u used the maya renderlayer occlusion-preset? this one renders pretty fast and clean most of the time....

cheers
OLi

[alesmav]

Thanks Oliver, yes I use default Occlusion preset. I did a ton of projects using it, but with with my character, I can't figure what bogs it down. Perhaps it has something to do with geometry history (wrap deformed geometry, etc), I don't know... I guess it's a very specific problem so I will probably have to accept the longer render times. Thankfully I have a lot of CPU power at my disposal...

Ales

[rygoody]

You could try setting up the FG AO in mental ray.

Or you could try rendering out occlusion passes with Nvidia Gelato, it's faster than MR for that and its free.

Or you could try Turtle, it has very good occlusion and it's cachable.

[ghostlake114]

@rygoody: could you tell me more about speed of AO in gellato , I will immediately use Gelleto for my AO pass If it really faster. We have only limited resources of rendering machine, so any tips to speed up rendering will be great

[Ultrasonic]

I think Gelato gives you a different anti aliasing then MR and you can run into trouble with that i fear....i have seen some fast AO renders from gelato but their quality wasn't that cool....but fast....if you try it please give some feedback to this thread....

c ya
Oli

[Bitter]

If you are using Maya 2008 the ctrl occlusion has the caching algorithm built-in to speed up occlusion in Maya. If you have Maya 2008 P03 from Autodesk (the current build if you are a Subscriber) there is a fast occlusion shader that does the same thing. It requires mental ray 3.6. It is faster but I haven't run it for an animation yet.

[alesmav]

Thanks for all the replies! I really have to try out some other occlusion render engines. Mental ray Occl can be slow at times. But then again, I am using maya 7.01 (didn't want to switch maya version in the middle of production), so I guess the occl should be more optimized in the later versions.

Btw, I found out what was causing the abnormal render times for my occlusion pass - I had some head elements (eyes, eyelashes, hat...) in NURBS geometry and it was at those exact places that render bogged down dramatically. I know... I should optimize NURBS tesselation values for mental ray render. But I just converted those surfaces to polys and the render times became healthier.

Thanks again!

Ales

[Bitter]

Under the render settings you can place a global override for the NURBS approximation. I do that a lot and render times decrease insanely sometimes. I love NURBS, I know I'm weird.

[noizFACTORY]

Gelato's ambient occlusion pass is indeed fast and also easier to set up. All one needs to do is turn on the ao pass check box in the gelato render globals. I don't see why it shouldn't be as good as any other ao pass when tweaked correctly (the max error and the max pixel distance being the ones to watch out for). I've often used it in production, especially when i'm rendering ao with transparency maps which can be a major pain to set up in mental ray (anyone knows any alternative to the current method of using a mib transparency shader?).
Do check out gelato's ao and see if it suits your needs.

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