Baking Normal Maps from a High-Poly AI Mesh

Prerequisites

• A final low-poly with non-overlapping UVs (retopology in Blender, then UV and texture fixes). The manual says baking requires a UV map. Polycount’s baking guide adds that only one copy of any overlapping or mirrored UV shell should stay in the 0-1 square at bake time.
• The untouched original mesh, kept for this. If you remeshed the only copy, the detail is gone.
• Both objects aligned in the same position and at the same scale. Polycount calls resetting the low-poly’s transforms before a bake “very important”, because compounded rotation and scale make a messy local space; in Blender that is applying rotation and scale.
• Cycles as the render engine. The manual says Cycles uses the render settings (samples, bounces) for baking.

Two preparations are worth making on AI meshes. Join the source if it arrived as many objects: the manual notes a fixed CPU memory footprint for every object you bake from and suggests joining high-poly objects to avoid running out of memory. And consider reducing an extremely dense source: Polycount says triangles smaller than the bake pixels increase bake time significantly without improving the bake.

Steps

1. Add a target image. On the low-poly’s material, add an Image Texture node with a new blank image sized for your target, and leave that node active and selected. The manual is blunt about this: if a material has no active and selected Image Texture node, “nothing will be baked for this material”, so a low-poly with several material slots needs one in each. The other Output Target is Active Color Attribute.
2. Set the image to Non-Color. The manual’s color space page names baking normal maps as a case where images should be marked as non-color data, since they store data rather than colors. Do it now on the Image Texture node’s Color Space field.
3. Select high-poly, then low-poly last so the low-poly is active. In Bake, enable Selected to Active. Rays are cast from the low-poly inward toward the high-poly.
4. Set Bake Type to Normal. Space can be Object or Tangent. The manual calls Tangent the default and “the right choice in most cases”, since the map then works on animated objects too. The manual says the setting on the Normal Map node should match the one used for baking.
5. Set the ray reach, using the table below.
6. Set the margin. Under Margin, choose Extend or Adjacent Faces and a Size in pixels. The manual says a margin avoids discontinuities at UV seams caused by texture filtering and mip-mapping. Clear Image wipes the target first.
7. Make a test bake. Polycount recommends testing at a smaller image size and lower quality until the errors are gone, then raising the settings for the final.
8. Bake, save the image, and connect it through a Normal Map node.
9. Bake color too, if needed. To carry the generator’s color onto the new UVs, use Bake Type Diffuse with Contributions set to Color only, leaving Direct and Indirect off. The manual says that with only Color selected you get the pass color, a property of the surface that does not depend on sampling. Any lighting painted into the AI base color comes along with it. Check metal parts afterward: StraySpark, which sells a bake add-on, says Cycles’ diffuse color pass is weighted by (1 − metallic), so baking base color this way turns fully metallic areas black, and that its own tool bakes through a temporary emission swap instead. Bake Type also lists Roughness, Emit and Ambient Occlusion (which ignores scene lights). The list has no Metallic entry.

Choosing the ray setup

No number in the manual tells you what distance to use, because it depends on how far your low-poly sits from your high-poly. Our suggestion: find the largest visible gap between the two surfaces, start a little above it, and change one value at a time.

Too much distance has a specific look. Polycount’s example is the gap between fingers: a large ray distance makes the baker pick up the neighboring finger, while a small one misses detail where the meshes sit further apart. If no single value works, its listed remedies include editing the cage by hand, or “exploding” the parts apart by the same offset on both meshes before baking and moving them back afterward.

Margin is linked to your UV layout. Blender’s Fraction margin method makes this checkable: per the manual, 1/1024 on a 1024-pixel texture gives each island 1 pixel of margin and keeps islands at least 2 pixels apart. Applied to an illustrative 2048 texture, a Fraction margin of 4/2048 leaves 4 pixels around each island and at least 8 between them, which tells you how large a bake Margin Size the layout can hold before neighbors collide.

Which way is green? Normal map conventions

The two common conventions differ only in the green channel, so a mismatch makes raised details look dented under moving light. What each destination documents:

To test, put the map on a mesh in the engine and move a light across a detail you know is raised. If it reads as a dent, flip the green channel in the engine’s texture settings or rebake with the green Swizzle inverted.

What goes wrong with AI meshes

These pair causes from the manual and Polycount with what to expect on generated meshes; the frequency on any given generator has not been measured.

Tangent space is one more reason to export the mesh you baked on. The glTF specification says that when tangents are not specified, clients should calculate them with MikkTSpace, so a file with no stored tangents depends on the importer doing so. Blender’s glTF exporter has a Tangents option under Mesh.

After the bake

Build LODs from the baked low-poly, then check the result in your engine. Method choice is on retopology for AI 3D models, and this page is part of the Cleaning Up AI 3D Models section.

Stop when the low-poly shows the major surface detail in engine lighting at gameplay distance. Chasing exact visual match to a million-triangle source is wasted effort for assets that appear small.

Not verified

Unreal’s and Unity’s normal map convention from their own documentation, and Blender 4.5 LTS menu wording. The manual gives no recommended ray distance or margin size. Bake screenshots and visual diffs are planned, not done.