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  1. #1
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    Ambient Occlusions in Maya. When to use them?

    Hello,

    I've been scanning the internet for Ambient Occlusions in Maya and it seems like the only answers are cryptic ones. No one seems to be able to explain in plain English... What is Ambient Occlusions? When should you use it? What is it good for? It has to do with shadows that are assigned by a texture map? Shadows which are not animate-able?

    I know how to export them from Mudbox, but how are they applied in Maya? What is a good method? Does anyone know of tutorials on shading networks that include Ambient Occlusions?

    Are they practical for character animation or just environments? Can they be use with misss_fast_skin shader in Mental Ray?

    An answer to any of these questions would be appreciated.

    Regards.
    Last edited by legman; 07-20-2010 at 06:20 AM.

  2. #2
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    Here is a pretty good overview of what AO is.

    Ambient occlusion is a calculation of lighting and shadows measured from the ambient (or bounced) light in a scene. Think of how the world looks on an overcast day, in which you don't really have much of a direct source of light. All light from the sun is being bounced around by the cloud cover. Think of how the shadows look. Generally soft and fuzzy, and they will accumulate more thickly on areas close to another surface, especially the ground. That's just about exactly what AO calculates. How those shadows will look.

    However, as I'm pretty sure you can imagine, that kind of calculation takes time. Lots of time. You're bouncing anywhere from thousands to millions of simulated light rays all across your surfaces to figure out what areas are lit and which ones are not. If you're creating a scene that has a lot of ambient light, and in many cases even when you're not, you can boost the realism of the scene and greatly speed up render time by applying AO to the environments. However, it would be important to mention that you would want texture-based AO to only be used on static elements of an environment. For instance, if you used AO to create a really nice soft shadow under a box, but then at some point the box gets moved, the shadow will stay; obviously, that's a problem.

    But that is isn't to say that AO is only for environments. It can be very useful for characters, as well; especially in those places where lighting is relatively static and doesn't do anything too overboard, such as shining a searchlight at them from underneath. For example, if a character is going to be outside a lot and is going to be in relatively the same pose most of the time (not doing flips and whatnot) then it's probably safe to say that they won't get much light from underneath. You can use AO to create some soft shading across the character to darken up surfaces that are facing toward the ground. The more the light will change in the scene, the more careful you have to be with this, but there's still a lot of room for flexibility before it just starts to look like soot or black paint on the characters.

    I hope this helps for starters.
    Last edited by Zak; 07-20-2010 at 02:05 PM. Reason: Typos

  3. #3
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    Zak, you are a veritable treasure trove of information. Now I will go be jealous elsewhere

  4. #4
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    milwaukee wi
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    I could be way off, but I believe AO's can be usfull for these two reasons.
    1. In compositing it gives another layer of shadows/midtones that you can adjust as you wish.
    2. Arn't they used in video games along with texture maps to keep poly count low, while keeping some sort of realism.

    I could/probably am wrong, but that was two things I thought I have used in the past.

    Kevin
    www.Somnium.Tv

    "When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been and there you will always long to return."
    -DaVinci

  5. #5
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    No, Kev, you're right on top of things.

  6. #6
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    Thanks for the info. I've been getting deeper into Rendering techniques and have started learning about Final Gather and Global Illumination. It seems Global Illumination is more practical for film production in general. I know they can be used together but I don't have any methods for combining Final Gather and Global Illumination.
    Last edited by legman; 07-27-2010 at 05:34 PM.

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