Heath Ledger could appear in his last film courtesy of computer wizardry - unless its director persuades Johnny Depp to step into his role instead.

The young Australian actor died in New York last week during a break from the filming in London of The Imaginarium of Doctor Parnassus, a $30 million fantasy movie directed by Terry Gilliam.

His co-star Christopher Plummer told People Magazine that Gilliam was "terribly saddened" by Ledger's death and "trying to work out at this moment how to continue on".

"Fortunately, because the film deals with magic there is a way, perhaps, of turning Heath into other people and then, using stills and I think they call it CGI (computer-generated imagery)," he said.

"Terry was a very good friend [of Ledger]. He very wants to go on with the movie, and I can very much understand why. Because he wants to dedicate it to Heath, of course."

In The Imaginarium of Doctor Parnassus, Ledger played a mysterious new member of a magician's troupe. Plummer plays the eponymous magician who has developed extraordinary powers by trading them for his teenage daughter's life in a deal with the Devil.

The recent location shooting in East London meant that filming was about one-third complete when Ledger was found dead in his Manhattan apartment. Cast and crew were due to get together again in Toronto next week, although that was called off as soon as news emerged of the actor's death.

It would not be the first time that CGI had been used to complete a role. It was used most notably after the death of Oliver Reed to finish off the actor's performance in Ridley Scott's Gladiator, although in that case shooting was much closer to completion.

An alternative for Gilliam, notorious as a director whose projects hit unexpected snags, is to appoint another actor to take over in Ledger's role, specifically after a scene when his character steps through a magic mirror. The American Johnny Depp, who has worked with Gilliam in the past, is seen as the most likely contender.

In his People interview, Plummer said that Ledger had been in "very high spirits" during filming in London. "He was just enjoying himself tremendously. It's a rather fanciful script, and he was wonderful in this role," he said.

But he confirmed that the actor had not been feeling well on set. He said: "We all caught colds because we were shooting outside on horrible, damp nights. But Heath's went on and I don't think he dealt with it immediately with the antibiotics.

"I think what he did have was the walking pneumonia... He was saying all the time, 'dammit, I can't sleep'…and he was taking all these pills."

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