The Na'vi were created by "performance capture", where actors' movements and expressions are translated into animated CG characters
By Tim Masters
Entertainment correspondent, BBC News
Director James Cameron declared himself to be "King of the World" when Titanic scooped 11 Oscars in 1998. As he returns in 2009 with his much-hyped sci-fi epic Avatar, he appears to covet an even grander title.
But Avatar's leading man, Sam Worthington, recalls a story from the pre-shoot stage of Avatar that casts Cameron in a more humble light.
The Canadian director took Worthington and co-star Zoe Saldana to Hawaii for four days to experience life in a rain forest.
"We were wearing nothing but a lace g-string... and a weird wig," says Worthington. "I thought Hawaii was going to be a holiday to be honest. I thought I'd take my surfboard and go surfing.
"We get there and we work and this guy comes past and says 'What are you doing?' I said 'We're making a movie'.
"He says: 'Big budget movie. Who's the director?' I said, 'That bloke over there'. And there's Jim with a handycam. He goes: 'Is that James Cameron? He's gone downhill since Titanic!'"
Titanic grossed more than $1.8bn (£1.1bn) worldwide, so it's no surprise Cameron's finished product shows no evidence of shaky handycams.
Cameron - here with wife Suzie Amis - came up with Avatar before Titantic
Avatar is a visually stunning live action film, set in a CG world - in 3D.
After Titanic, Cameron is back in familiar territory. The Terminator (1984), Aliens (1986), The Abyss (1989) and Terminator 2: Judgment Day (1991) all pushed the limits of action and visual effects.
Reviews have been largely positive ahead of Avatar's release this week, despite the film earning early nicknames like Dancing With Smurfs and Smurfahontas.
The Smurf jokes refer to the Na'vi - the race of blue-skinned humanoid creatures who live on the distant world of Pandora. They have feline faces, long tails and stand 10 feet tall - and are threatened by colonists from Earth who want to plunder their moon for a precious mineral.
Worthington (who appeared in wham-bang action flick Terminator Salvation) plays Jake Sully, a wheelchair user who is able to walk again through his "avatar" - a remote-controlled Na'vi hybrid that allows him to bond with the indigenous tribe.
He also falls in love with a blue-hued local girl - played by Saldana.
Sigourney Weaver worked with Cameron on Aliens
The alien Na'vi were created by "performance capture" in which the actors' movements and expressions were translated into animated CG characters.
Sigourney Weaver, who plays scientist Grace Augustine, says she was surprised when she saw the final result.
"I found that Grace looked just like Sigourney, only I was 10 feet tall and blue, and a much improved version of myself - 30 years younger - and can leap tall buildings in a single bound," she laughs.
Cameron, who directed Weaver in Aliens more than 20 years ago, says he found the performance capture process allowed him to focus on getting the best out of his cast.
"It's probably the best director-actor relationship and working process I've ever been involved in.
"I'm not distracted by the lighting, the time of day, there's the sun setting - do I have to get the shot by 6.15? And where's the dolly track going to go? - and a thousand questions that pull the director's mind away from the process of working with the actors..."
It's no secret that Cameron conceived Avatar before he made Titanic, but waited a decade for technology to catch-up with his vision.
Every aspect of the alien world Pandora - the plants, insects, mountains and clouds - is computer-generated, but looks photo-realistic.
Some geeky facts: The creation of Pandora required over a petabyte (1m gigabytes) of digital storage.
By comparison, it took 2,000 gigabytes to create and sink the Titanic - about 1/500th of the amount used for Avatar.
A lot of time, effort and money went into creating the CG world of Pandora
"The film espouses this love/hate relationship with technology," says Cameron. "Obviously we use technology to tell this story that's a celebration of nature, which is an irony in itself.
"It's not that technology is bad, it's not that technological civilization is bad, it's just that we need to be in control of the technical process.
"We're not going to be able to just rip our clothes off and run back into the wilderness - first of all, there's not a whole lot of it left, secondly, that's not going to work for eight billion people.
"So we're going to have to think our way out of this, we'll have to do it using technology and using science, but we're also going to have to be very, very human about it."
Cameron adds: "One of the themes of the film is symbolised by the fact that it begins and ends with the main character's eyes opening - it's about a change of perception, and about choices that are made once our perceptions change."
Cameron has constructed his alien epic in 3D, which he sees as an important part of big screen spectacle.
He says "cinema has done very well compared to most businesses" during the economic downturn, but "we need something that kick-starts public enthusiasm for the cinema as an experience".
"As people seem to be going down to smaller and smaller devices and watching movies on iPhones, we need to do something to reverse that trend or at least to balance it, so I've certainly set as my goal making the movie theatre back to the sacred experience it's always been for me in my whole life, and 3D is part of that."
These are interesting times for box office economics.
The release of Avatar - thought to have cost more than $200m (£123m) - comes shortly after the micro-budget Paranormal Activity.
The horror hit was shot on a camcorder for $15,000 (£9,000), but has taken more than $100m (£60m) in the US alone - making it one of the most profitable films of all time.
The money matters because if Avatar sinks like the real Titanic at the box office it puts a question mark over two possible sequels.
"All these CG mountains and plants and trees and leaves and flowers and buds and creatures - I mean, everything that you saw up there on the screen - had to be made by people at workstations over a period of years, and so they have value," says Cameron.
"So I feel like I have to make a second one now, but that'll only happen if we make some money with the first one. So we'll see... I have a story worked out for the second film, and the third film, but my lips are sealed."
Avatar opens across the UK on 17 December.