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Light Maps and Ambient Occlusion Maps

What's the difference in baking a light map versus and ambient occlusion map.Why would I want to do one as opposed to the other?

Also what's the difference between light Tracer and Mental Ray as an Ambient Occlusion map can only be baked with mental ray?

Lastly what is the best setup for either of the two (apply a white diffuse color or a light tracer material to the mesh?)


  • EarthQuake
    Can both be used for/as the same thing. A lightmap generally refers to directional baked lighting, for games this will be on a 2nd uv set for environment stuff. However, if you bake a lightmap in max with just a skylight and no direction lights, its AO. No difference..... Light Tracer/Mental ray, differences will be quality and speed, best to just do some tests and see for yourself.
  • Bigjohn
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    Bigjohn polycounter lvl 9
    Ambient Occlusion represents shadowing that comes from the environment itself, not from any particular lightsource. I like to think of it as the shadows being cast by bounced light, as opposed to the shadows being cast directly by a light.

    A light map is baking any lighting information into a map. You could set up a bunch of lights, and then bake that into a texture to then use for whatever purposes.

    A shadow map is when you bake only the shadows being cast. This is one way to get an Ambient Occlusion map, by baking a shadow from a light that simulates bounce light, like 3dsmax's Skylight. But you don't necessarily need a light to bake an AO. There are AO shaders, like Mental Ray's, which generate those shadows based on the objects in the scene.

    At any case, the reason AO is so popular, is because it adds quite a bit of volume and depth to an object, without hinging on a lightsource. This is great for video-games, as stuff tends to move around, and the light direction can change. So if you bake really strong shadows that look like they're coming from above, and then in-game the light moves to the side of an object, or below it, it will look real weird. AO doesn't have that problem.

    Baking a lightmap though, is something I never quite got the hang of. You basically set up a scene with some cool lighting, then bake that to use as an addition or a base in your texture.

    Hope I was helpful.
  • Jacecr
    Definitely helpful,thanks!I was following tutorials and got confused as to why AO maps were used sometimes and light maps used in other instances.
    I modeled a tank recently and used a light map instead of an ambient occlusion map unknowingly.The light map is more subtle but when I try to bake an AO map above 512x512 max craps out.The 512x 512 AO map is harsh.
  • Bigjohn
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    Bigjohn polycounter lvl 9
    Those look fine. The noise you're getting on the second image is because of not enough detail in the AO. Depending on how you're baking it, you wanna increase the rays being cast, or samples amount. Check out the wiki here on Polycount, there's plenty of information on that stuff.
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