If you are a Blender user, this addon I created might be interesting for you:
This is a program to generate normal-, spec- and displacementmaps from image textures in one go. It supports stack processing and a few other nice features, but has some rough edges and is still in development.
See the releases section. Usually there are Windows (32 bit) and Linux (64 bit) binaries available on each release.
- Fully multithreaded with OpenMP, will use all available CPU cores
- Keep Large Detail (see below for details)
- Fast and easy way to create normal, spec and displacementmaps
Keep Large Detail
One of the things I hate about classic normalmap generators is how they handle large image textures: usually the normalmap is unusable due to fine detail and the whole information about "large detail" (the overall curvature) is lost.
What the feature I called "Keep Large Detail" does is that it blends a downscaled version of the image over the original image, thus retaining the overall curvature information while still showing fine detail: