Normal maps from height textures for better bump in renders
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When I render SketchUp models in a realtime engine, flat photo textures often look disappointingly flat under raking light. Bump maps help, but engines respond much better to tangent-space normal maps, and a lot of free texture sites only ship a grayscale height or displacement map.
The workflow I've settled on:
- Start with any grayscale height texture (bricks, ripples, weave, etc.).
- Convert it to a tangent-space normal map. Lately I use a small browser-based tool for this, normalmapbench.com, because it runs entirely locally (the texture never leaves the machine, which is handy for client work) and it previews the result under a movable light before you export a PNG. It also gives both OpenGL and DirectX variants.
- In your renderer's material editor, load the normal map into the bump/normal slot, and keep the height map for displacement if the engine supports it.
Two things that tripped me up:
- Green channel direction matters. If the surface detail looks inverted, switch the Y convention (OpenGL vs DirectX) instead of fighting the intensity slider.
- Soften the source height map a little before converting. Noisy height data turns into sparkly, glittery normals under sharp sunlight.
Full disclosure: I built normalmapbench, so take the recommendation with a grain of salt — but the local-preview workflow is what I actually use on client models. How do others here generate normal maps for rendering work?
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