Lucasfilm engineers created THX, which was designed to help theaters create the best sound for movies through a system that the Lucas company certifies meets its technical standards. THX, which was spun off from Lucasfilms in 2001, also certifies home entertainment systems, consumer electronic products and automobile sound systems.

Hollywood studios have a generally poor record owning effects companies, said Scott Ross, a former general manager of ILM and one of the founders of effects company Digital Domain.

Disney bought Dream Quest Images in 1996 and shuttered it five years later. Warner Bros. also has shut or sold off effects companies it acquired. Only Sony Corp has found success with its Imageworks effects unit.

Studios usually discover that running an effects business is costly and foreign competitors can do the job cheaper, Ross said. "They come to the conclusion that running a visual effects company is not a profitable business," Ross said.

Iger, in announcing the deal to Wall Street analysts, praised ILM's work and said he had no immediate plans to change it. "It's been a decent business for Lucasfilm and one we have every intention of staying in," he said.