Originally written by ascottk on http://forums.thedarkmod.com/topic/4244
Since this issue has come up a few times while looking at the textures, I thought I may post a way to visually check to see if the normal map has been generated correctly.
The normal map should look like it's been lit up by different colored lights like this:
And another issue that's come up is generating normal maps, via the nvidia normal map plugin, straight from the diffuse texture. Here's a tutorial link to make normal maps from height maps:
You have to be careful with gradients if you want rounded edges. This plugin interprets those as being angular so you have to use a gaussian blur in order to get decent rounded edges.