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