Getting rid of sparkling artifacts in BM/PM/DM

How can you get away from artifacts caused by minifying, magnifying normal map. Mips doesnt seem to give good enough results, aniso doesnt seem to help too. I’ve seen such artifacts in 3DM05 scene 1 also (sparkling ground), so is this even possible at all.

NVidia has an excellent paper on mipmapping normal maps (I don’t have a link handy). In addition to solving the “sparkles” problem, you get free gloss-mapping to boot. I’ve implemented this technique, and it works like a charm.

I think I’ve seen an article about normal-mipmap generation on NVIDIA’s site. Ah, there it is:

Check this too, it mentions renormalization for magnification: