special effect

Special Effects
For The Two Towers, Weta Digital doubled their staff[18] of 260.[19] In total, they would produce 73 minutes of digital effects with 799 shots.[18] The film would feature their first challenge in creating a battle scene, as well as creating two digital characters who needed to act rather than be a set piece, unlike the previous film's Cave Troll and Balrog.[14]
Gollum
Weta began animating Gollum in late 1998 to convince New Line they could achieve the effect. Andy Serkis "played" Gollum by providing his voice and movements on set, as well as performing within the motion capture suit later on. His scenes were filmed twice, with and without him. Originally Gollum was set to solely be a CG character, but Jackson was so impressed by Andy Serkis' audition tape that they used him on set as well.
Gollum's CG model was also redesigned during 2001 when Serkis was cast as Sméagol, Gollum's form before he is cursed by the One Ring, so as to give the impression Andy Serkis as Sméagol transforms into the CG Gollum. The original model can still be glimpsed briefly in the first film. So over Christmas 2001 the crew proceeded to reanimate all the previous shots accordingly within two months. Another problem was that the crew realized that the cast performed better in the versions of the film with Serkis. In the end, the CG Gollum was rotoscoped and animated on top of these scenes. Sometimes due to Gollum not being human, they fully animated some shots such as him crawling upside down. Serkis' motion capture animated the body whilst animators did the head. Gino Acevedo supervised realistic skin tones, which took four hours per frame to render.[20]