pmu
Well-known
Topaz Gigapixel doesn't really "preserve the detail and sharpness". Sure, it uses what you've got, but when you make a large print, it guesses what would have been there if you had used a higher resolution sensor, and adds it in. From what I have seen, it does a pretty good job of guessing.
This is how I understood it also. It's the AI doing it's thing.