How to make accurate normal map in Photoshop?

[kirkr5689]

From something like this  i.e heigh/depth image:

Looking accurate and not like what filter ->3d -> generate normal map doing.

I.e not like this :

blurry mess that filter is doing.  

Should I know something about this filter  to make actual normal map?   

Is there any action/script  that could do a normal map for real?

Looks like it's possible in 32 bit mode by embos filter, levels and gamma fix .     I don't need blue channel btw.     Does anybody knows how to do it mathematically correct way and in 16 bit mode?