What is Normal map?

Lighting depends on the direction a surface faces (its normal). A normal map stores a direction per pixel, encoded as RGB colour, which is why normal maps look purple-blue. The renderer uses those directions instead of the flat polygon's, so light catches bumps and grooves that aren't in the geometry.

Why it matters

It's the core trick of real-time 3D. Artists sculpt millions of polygons of detail, then bake it into a normal map on a light mesh. The carved chess king in our library is a clear example: under 4,000 triangles, but the carving reads in full.

Limits

• The silhouette doesn't change. Edges still show the low-poly shape.
• The effect weakens at grazing angles.
• It doesn't 3D print. Printers only see geometry. For real raised detail, use a displacement map.

OpenGL vs DirectX

There are two conventions, which differ in the direction of the green channel. If bumps look like dents, flip the green channel. glTF uses the OpenGL (Y+) convention.