法线贴图是用来解决低模的细节表现问题

法线贴图制作工具

NVIDIA Texture Tools for Adobe Photoshop

A collection of texture tools generating normal maps, texture compression, mip map generation and cube map formatting packaged as a plugin for Adobe Photoshop 5.0, 5.1, 6.0, 7.0, CS, CS2, CS3, CS4, CS5 and CS6.

 

https://developer.nvidia.com/nvidia-texture-tools-adobe-photoshop

如果想详细了解法线贴图的原理，请阅读

http://www.nvidia.com/object/real-time-normal-map-dxt-compression.html