Want to try Samsung Galaxy S4 Camera? Yes, you can do so on your Samsung Galaxy S3. Well, it is for leaked Android 4.2.1 Jelly Bean XXUFMB3 firmware only (for the moment).
Rest assure that you can enjoy most of the Galaxy S4 features on your Galaxy S3 (if not limited by hardware), developers will port most of the stuffs sooner or later.
So far, these Galaxy S4 camera features are working – Rear camera (up to 8mp setting), front camera, flash, Beauty Face, Best Photo, Best Face, Sound & Shot, HDR, Eraser, Sports and Night features.