A year ago I wrote a program that creates the Normals dds files for SH4.
You needed no other Graphics program to use it.
If there is interest in this tool,
I'll adjust the Code to create the Normals dds files as they are now in SH5.

The code is based on Nvidia's Texture Tools source code.
So it's like haveing thier Normals filter in PhotoShop.
But you don't need PhotoShop.