chris_b
06-13-2003, 11:44 PM
I pulled this from a post further down
the line where it wasn't getting much attention. It is a very useful technique that deserves a thread and discussion of its own.
"At SIGGRAPH 2002, technical directors from Industrial Light and Magic presented a technique they call ambient occlusion. Simple, but highly effective, ambient occlusion's been used for years at studios like BlueSky and ILM to achieve grounded realism, without the cost of full global illumination. Fancy name aside, ambient occlusion is simply a ratio of how much ambient light a surface point would be likely to receive. It simulates a huge dome light surrounding the entire scene. If a a surface point is under a foot or table, it will end up much darker than the top of someone's head or the tabletop. This can then be multiplied by various other surface attributes to achieve a subtle, but very powerful, lighting effect"
_
Ambient Occlusion is a great means of regaining most of the depth of a full GI render at a fraction of the cost. Best of all, once you have the Ambient Occlusion pass you can re-use it even if you change the textures and lighting.
http://www-viz.tamu.edu/students/bmoyer/617/ambocc/
http://zj.deathfall.com/occsurfii.htm
http://zj.deathfall.com/img/ambocc_dia.jpg
In Cinema there are currently two methods that I know of :
i) The One Bouce GI pass:
- Render a pass of your scene with
all materials and direct lighting (no radiosity).
- (optional) Render and Ambient Illumination pass using a blurred environment map of the scene (this
is a workaround for getting back your diffuse bounce light).
- Apply a 100% white material with no specularity to every object in the scene
- Apply a 100% luminous material to a Sky Object
- In your render settings enable Radiosity (either mode) and set the Diffuse Depth to 1 and render (ensure that the view angle and dimensions are exactly the same as the straight render)
- In Photoshop or your compositing application, place the Ambient Illumination pass on the first layer,
the Ambient Occlusion pass on the next layer above (multiply), and the Direct Illumination pass on top (screen).
ii) The Shader-Based approach
- Render the Direct Illumination and Ambient Illumination passes as above.
- Apply a 100% luminous material with no specularity to every object in the scene and place dirtyNUTS in the diffusion channel (more rays for smoother results)
- Add an Environment object and set the Strength to 100%.
- Render and combine passes as above.
The one bounce GI method is more suitable for outdoor environments and the dirtyNUTS method is better indoors.
Also, dirtyNUTS tends to be faster.
If anybody is using this technique, please chime in and add your thoughts!! Surely it would be possible to write an optimised shader for generating AO passes? :)
the line where it wasn't getting much attention. It is a very useful technique that deserves a thread and discussion of its own.
"At SIGGRAPH 2002, technical directors from Industrial Light and Magic presented a technique they call ambient occlusion. Simple, but highly effective, ambient occlusion's been used for years at studios like BlueSky and ILM to achieve grounded realism, without the cost of full global illumination. Fancy name aside, ambient occlusion is simply a ratio of how much ambient light a surface point would be likely to receive. It simulates a huge dome light surrounding the entire scene. If a a surface point is under a foot or table, it will end up much darker than the top of someone's head or the tabletop. This can then be multiplied by various other surface attributes to achieve a subtle, but very powerful, lighting effect"
_
Ambient Occlusion is a great means of regaining most of the depth of a full GI render at a fraction of the cost. Best of all, once you have the Ambient Occlusion pass you can re-use it even if you change the textures and lighting.
http://www-viz.tamu.edu/students/bmoyer/617/ambocc/
http://zj.deathfall.com/occsurfii.htm
http://zj.deathfall.com/img/ambocc_dia.jpg
In Cinema there are currently two methods that I know of :
i) The One Bouce GI pass:
- Render a pass of your scene with
all materials and direct lighting (no radiosity).
- (optional) Render and Ambient Illumination pass using a blurred environment map of the scene (this
is a workaround for getting back your diffuse bounce light).
- Apply a 100% white material with no specularity to every object in the scene
- Apply a 100% luminous material to a Sky Object
- In your render settings enable Radiosity (either mode) and set the Diffuse Depth to 1 and render (ensure that the view angle and dimensions are exactly the same as the straight render)
- In Photoshop or your compositing application, place the Ambient Illumination pass on the first layer,
the Ambient Occlusion pass on the next layer above (multiply), and the Direct Illumination pass on top (screen).
ii) The Shader-Based approach
- Render the Direct Illumination and Ambient Illumination passes as above.
- Apply a 100% luminous material with no specularity to every object in the scene and place dirtyNUTS in the diffusion channel (more rays for smoother results)
- Add an Environment object and set the Strength to 100%.
- Render and combine passes as above.
The one bounce GI method is more suitable for outdoor environments and the dirtyNUTS method is better indoors.
Also, dirtyNUTS tends to be faster.
If anybody is using this technique, please chime in and add your thoughts!! Surely it would be possible to write an optimised shader for generating AO passes? :)