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material in the scene. A number of revolutionary visual effects techniques were used in the production of Avatar. According to Cameron, work on the film had been delayed since the 1990s to allow the techniques to reach the necessary degree of advancement to adequately portray his vision of the film. The director planned to make use of photorealistic computer-generated characters, created using new motion-capture animation technologies he had been developing in the 14 months leading up to December 2006. Innovations include a new system for lighting massive areas like Pandora's jungle, a motion-capture stage or "volume" six times larger than any previously used, and an improved method of capturing facial expressions, enabling full performance capture. To achieve the face capturing, actors wore individually made skull caps fitted with a tiny camera positioned in front of the actors' faces; the information collected about their facial expressions and eyes is then transmitted to computers. According to Cameron, the method allows the filmmakers to transfer 100% of the actors' physical performances to their digital counterparts. Besides the performance capture data which were transferred directly to the computers, numerous reference cameras gave the digital artists multiple angles of each performance. A technically challenging scene was near the end of the film when the computer-generated Neytiri held the live action Jake in human form, and attention was given
Visual effects
to the details of the shadows and reflected light between them. The lead visual effects company was Weta Digital in Wellington, New Zealand, at one point employing 900 people to work on the film. To render Avatar, Weta used a 10,000 sq ft (930 m) server farm making use of 4,000 Hewlett-Packard servers with 35,000 processor cores running Ubuntu Linux and the Grid Engine cluster manager. The render farm occupies the 193rd to 197th spots in the TOP500 list of the world's most powerful supercomputers. Creating the Na'vi characters and the virtual world of Pandora required over a petabyte of digital storage, and each minute of the final footage for Avatar occupies 17.28 gigabytes of storage. To help finish preparing the special effects sequences on time, a number of other companies were brought on board, including