Normalize TB (Tangent Basis)

In 3D baking, the option to “normalize TB” (Tangent Basis) refers to a process where the tangent and bitangent (or binormal) vectors, which form the local coordinate system (tangent space) of a 3D model, are re-normalized so they are unit length (a length of 1.0) and exactly perpendicular to each other and the surface normal at every point. 

– Explanation and Purpose:

• Tangent Space Normal Mapping: Tangent space normal maps are widely used in real-time graphics because they allow the same normal map texture to be reused across different objects with varying orientations and deformations (e.g., animated characters). This is possible because the normal map’s data (RGB values corresponding to XYZ vectors) is relative to a local coordinate system at each vertex/pixel, rather than the global “world” coordinate system.
• The Tangent Basis (TBN Matrix): This local coordinate system is defined by three perpendicular vectors: the Tangent, Bitangent (or Binormal), and the surface Normal. These three vectors form a matrix (TBN matrix) used to transform lighting and view vectors into the correct space for shading.
• Normalization During Baking and Rendering: The vectors generated during the mesh creation or baking process may lose their perfect unit length and orthogonality due to interpolation across triangles, UV seams, or specific calculation methods.
  • Baking: Enabling “normalize TB” during baking ensures that the normal map is created using a perfectly normalized and orthogonal tangent space.
  • Rendering: It is also crucial that the real-time renderer (e.g., a game engine) uses the exact same tangent space algorithm and normalization method as the one used during baking to avoid shading artifacts or seams. Many modern engines use the MikkTSpace standard for consistency.
• Ensuring Accuracy: Normalizing the TBN vectors at the pixel level during rendering is a common practice to maintain lighting accuracy and prevent visual glitches, even if they were already normalized at the vertex level. 

In short, “normalize TB” ensures the mathematical integrity and consistency of the local coordinate system used for normal mapping, which is essential for correct and seamless shading across a model’s surface.