The actor, known for Dame Edna, had the media in stitches.
"It was thrilling to work on this film and when see my extraordinary interpretation you realise why I immediately fell into the arms of Jenny Craig, and minor cosmetic surgery," he said.
"I always thought motion capture was something you did when you were taking a specimen at the doctor."
Comedy is something that's more evident in JRR Tolkien's The Hobbit, which was written as a children's book, unlike the much darker tale of The Lord of the Rings.
Jackson said the lightness and the comedy in The Hobbit was a joy.
"It was one of the things that made it appealing," he said, adding it influenced the casting.
Aussie actors Cate Blanchett and Hugo Weaving returned to Middle Earth for the film, with Weaving saying: "there was something inevitable about coming back to do The Hobbit". British actor Sir Ian McKellen also returned as Gandalf the Grey. Meanwhile new cast members - including the 13 dwarves - and Martin Freeman, who took on the role of Bilbo Baggins are having their first taste of Middle Earth.
Jackson wanted Freeman so badly for the role, that when Freeman's television show Sherlock conflicted with The Hobbit's filming schedule, the director worked around it.
He shut down production of The Hobbit partway through to allow Freeman to return to the UK to film the second series of Sherlock.
"Which was a pretty radical thing to do," Jackson said.
"It's not the sort of thing you normally do on a film, but I'm incredibly pleased we did it, it's the best thing that ever happened."
Also arguably radical was when Jackson suggested people try to see the movies in 48 frames per second (fps), which is double the standard 24fps usually seen in films, because it creates a more realistic look.
Of the approximately 25,000 screens that will be showing The Hobbit in the coming weeks, only about 1000 will play the movie in 48fps Jackson said.
"This is something we've deliberately done because it is like you're sort of dipping your toe in the water," he said.
"The feeling that I have as a filmmaker is I have a responsibility to the technology that's available to us now and to think of ways in which that technology can be used to enhance the cinematic experience."
Jackson also hit out at PETA for urging protests against alleged animal abuse during filming for The Hobbit.
He said no animal abuse took place.
"Absolutely none. No abuse. Absolutely none. You've got a very radical political organisation that has jumped on this. Personally it's an insult to everyone who worked on this film. We care about we do. We care about all the animals. They are an organisation that every story that is written about the premiere, they want their name on it. It's pretty pathetic."
Freeman was prickly when asked whether, like his character Bilbo, he prefers a quiet life.
"If I do I'm f****d."
He would not comment on how similar he was to his character.
"I don't know how similar I am to Bilbo. I've got the same nose."
The Hobbit releases in New Zealand on December 14 and in Australia on December 26.
- AP