With many movies that depend on CGI to be precise, entertaining and believable, more than one effects house will work on different scenes so a movie can be released on deadline. As with James Cameron’s CGI blockbuster Avatar, Industrial Light & Magic was asked to help with a number of scenes in the film.
Oscar-winning visual effects supervisor John Knoll chats with Cnet about the role ILM played in helping with the movie’s hefty to-do list, working with Weta, and how ILM developed a way to make CGI explosions even more believable and entertaining.
Until now, big fiery explosions in CGI-heavy films have been shot with live camera and then had visual effects added to them. But Knoll said that because of some of the limitation of matching Cameron’s templates for “Avatar,” there was no practical way to meet the movie’s explosive needs with live-action.
“We’ve done CG explosions in the past,” Knoll said, “but never with this level of realism, and never this close up.”
Fortunately, ILM had pioneered the rendering of the visual movement of fluids in films like “Poseidon” and “Pirates of the Caribbean,” and Knoll knew that the shape and movement dynamics of an explosion were similar to that of water.
“The same underlying engine is being used on this,” Knoll said. “The motion of the underlying gas is similar to the motion of fluids. The medium is relatively uncompressable. So when there’s movement of the medium, it can’t change volume real dramatically. So if you push on one side, something has to push on the other side.”
That meant that ILM could take the graphics engine it had created for fluid shots in the previous films and apply the same basic technology for the explosions in “Avatar.” Though there are clearly some major differences between fluid and big fire–notably that as fuel burns, fire expands, and then retracts when the fuel goes away, the technique was similar enough that the technology could be adapted to the needs of “Avatar.”
“I think this is going to be an important technique (for the industry) in the future,” Knoll said, “to tailor-make an explosion that looks good close up.”
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ILM steps in to help finish Avatar visual effects