This strangely beautiful and hypnotic video comparison of 'The Hobbit:TDOS' Trailer vs Blu-Ray was posted over on FE.org:

https://www.youtube.com/watch?v=nJFfpIKfMU0

It's interesting to note now much a film can be manipulated, changed and fiddled with when it's shot on greenscreen like the PT. The Hobbit has way more sets than the PT but still so few that it can be messed with like this when only the foreground elements are live action.

It's not just that the PT had a lot of CGI shots, it's that every pixel was meddled with in the same way as The Hobbit so it all looked like fake CGI. And Lucas didn't just use CGI to clean up wig lines like in that Hobbit clip, he was doing crazy sh*t like chopping off actor's heads from one take and switching them to another body.