I made the image above in a 3D animation program, Blender (following a tutorial very closely!). It includes all the basic tools need to create objects, characters, effects, and animations. In a film such as Avatar, dozens of seperate programs would be used, with each one focusing on a specific area, such as model design, lighting, movement, the environment or editing (a list of programs used can be found here).
I added a basic rotation of the Earth with the camera in a fixed position. The animation lasted for 60 frames, at a standard 24 frames per second, which is less than 3 seconds. I rendered the animation, which means that the program basically 'draws' each frame, and then they play in sequence. Because of my ancient computer, it took about an hour to render all 60 frames.
Before Avatar was released, James Cameron told audiences that each frame of finished film takes 30-50 hours to render, then double that up for 3D.
So if that's 40 hours on average, and Avatar is 9720 seconds long (162 minutes), and it's 24 frames per second, then: 9720 x 24 = 233,280
So there are 233,280 frames in Avatar.
If each one takes roughly 40 hours to render, then: 233,280 x 40 = 9,331,200
Then double that for 3D, the whole of Avatar would take about 18, 662, 400 hours to render. That's 777600 days, or 2129 years. (That took ages, I hate maths).
Rather than releasing the film 2 millennia later, loads of highpower servers were used, such as the ones below (source).
Cameron is apparently planning to release Avatar 2 and 3 in 48 frames per second, becausehe belives that it "makes for better 3D". The Hobbit: An Unexpected Journey is shooting at 48fps.
But was it worth it? The film's profit shows that it probably was, and the effects created were very detailed and realistic.
The Thing experimented with a frame by frame method, although it was not nearly as technical. Stop-motion was used for the alien in the climax of the film, but Director John Carpenter didn't think that it looked believable to audiences, so it was deleted:
These particular examples show that, in this case, computer generated imagery is more effective than physical stop-motion.
Something else to consider when thinking about how believable something looks on screen is not just the effect, but the actor's reaction to the effect. When there is physically nothing in front of them, apart from perhaps a ball on a stick, they have to react to what they imagine is there, rather than what is there. In Alien, the actors apparently had no idea what would happen in the 'chest-buster' scene, and because everything in that scene was phyical, it lead to a more realistic reaction.
On a side note, The Dark Knight Rises was great, especially in Imax!
