bent normal vs object space

merwynl

Hi polycounters,

I'm curious to know what the difference is between a bent normal and a object space normal. I understand that bent normal bakes light information from a highpoly but is the difference between the two only in terms of its application?

cheers

Bartalon

This question came up in another unrelated thread briefly back in May. Here's the gist of what I got out of the short discussion:

1. There isn't much documentation on bent normal maps.
2. Bent normal maps rendered using xNormal are the exact same as Object Space normal maps, and regular normal maps with the "tangent space" option unchecked. Because of this, I will often bake out an object space normal map by just using the bent normal map option. This prevents me from having to initialize another bake just for OS normals.
3. Here are some resources on the subject:

http://eat3d.com/forum/questions-and-feedback/bent-normal-maps
http://pages.cs.wisc.edu/~ltokheim/ambenv/
http://www.valvesoftware.com/publications/2007/SIGGRAPH2007_EfficientSelfShadowedRadiosityNormalMapping.pdf

Hope this helps

Ashaman73

A object normal describes the surface, whereas the bent normal often describes the direction of the most incoming light. Bent normals are used in combination with ambient occlusion. A standard AO map only holds the darkening factor, a bent normal map although includes the direction where most of the potential light is incoming.
This way you have an ambient occlusion depending on the light direction. It could be used to look up ambient/diffuse light condition in a cube map or to calculate the diffuse light occlusion of light sources.

AlecMoody

Bartalon wrote: »

This question came up in another unrelated thread briefly back in May. Here's the gist of what I got out of the short discussion:

1. There isn't much documentation on bent normal maps.
2. Bent normal maps rendered using xNormal are the exact same as Object Space normal maps, and regular normal maps with the "tangent space" option unchecked. Because of this, I will often bake out an object space normal map by just using the bent normal map option. This prevents me from having to initialize another bake just for OS normals.
3. Here are some resources on the subject:

http://eat3d.com/forum/questions-and-feedback/bent-normal-maps
http://pages.cs.wisc.edu/~ltokheim/ambenv/
http://www.valvesoftware.com/publications/2007/SIGGRAPH2007_EfficientSelfShadowedRadiosityNormalMapping.pdf

Hope this helps

Can you post some testing showing that bent normals in xnormal are the same as object space maps? They shouldn't be the same thing and from the description jogshy posted in the eat3d thread I would assume they aren't.

Bartalon

xNormal's bent normal maps are identical to its object space normal maps down to the pixel hex code. Here's a bake:



I haven't really messed around with the bake settings for the bent normal maps, as I have never found a reason to, nor have I ever had the need of a "true" bent normal map. It's possible xNormal does bake occlusion information into bent normals with the right adjustments, but I've never done it. You'll have to try for yourself.

JustMeSR

I bake bent normal maps when I need both (Tangent and object space) types. :poly142:

I guess they are different once you change the bias option.

merwynl

wow, thanks for the info guys. I'm gonna have to start applying some of these into my own work now