Via Starwars.com:

FROM FULLY CG CHARACTERS TO NEW INNOVATIONS IN SHOOTING, THE PREQUEL TRILOGY REPRESENTS A LEAP IN DIGITAL EFFECTS.
The Star Wars saga is often lauded for its pioneering strides in the world of practical effects — we recently discussed some of the coolest of them — but Industrial Light & Magic (ILM) has done impressive work in the digital realm, too. Computers can see and achieve scenes that are beyond our grasp sometimes and can be just the thing to add depth or motion. Digital effects also work really well with those of the practical variety by extending them or giving them an extra oomph to make them leap off the screen. These digital effects in Star Wars broke the mold or created new molds.

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