What is the best way to blend two normal maps together? Why can’t I just add two normal maps together in Photoshop? I heard that to combine two normals together, you need to add the positive components and subtract the negative components, then renormalize. Looks right to me… Why shouldn’t I be using Overlay (or a series of Photoshop blend modes) to blend normal maps together? I want to add detail to surfaces. How does one combine normal maps in real-time so that the detail normal map follows the topology described by the base normal map?
We go through various techniques that are out there, and present a neat alternative (“Reoriented Normal Mapping”). Our mathematically-based approach to normal map blending retains more detail and performs at a similar instruction cost to other existing techniques. We also provide code, and a real-time demo to compare all the techniques. This is by no means a complete analysis – particularly as we focus on detail mapping – so we might return to the subject at a later date and tie up some loose ends. In the meantime, we hope you find the article useful. Please let us know in the comments!