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The bent normal is the direction where most ambient light comes from. The median ray that did not intersect the mesh.

It is not the same as object space normals. A bent normal map could be baked in object space or in tangent space.

Bent normal maps are used to for more realistic realtime shading (GI approximation, specular occlusion)

Some links of where I got the info:

So how would I bake a bent normal map using Blender (with Cycles)?

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  • $\begingroup$ Probably the solution is to create an OSL script node. $\endgroup$ Nov 14 '19 at 16:35
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I managed to write an Open Shading Language script that provides an ambient amount output (AO) and a direction vector from which the most ambient light came from. This can be used to create the bent normal map.

To use it, switch render engine to Cycles and enable the Open Shading Language checkbox.

For the object from which you want to bake the Bent Normals add a material if there isn't one yet. In the Material Node Editor add a Script Node and select this script: AmbientOcclusionDirection.osl

Make sure the input Normal node is connected to the Normal from a Geometry input node. And the output NonOccludedDirection node to the Normal node of the shader.

Bent Normals Noodle

Then bake as you would bake a normal normal map :-)

To check if the Distance and Samples settings are reasonable before baking, connect the AmbientOutput to the color and make sure the AO gradient is nice.

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