Harry Potter brings back the magic for the third time. Director Alfonso Cuarón (right) was anti-Terminator. He insisted that the film’s vfx be grounded in reality. All images unless otherwise noter © 2004 Warner Bros. Ent. Harry Potter Publishing Rights © J.K.R. Photos: Murray Close.

The highly anticipated third film in the phenomenal fantasy saga, Harry Potter and the Prisoner of Azkaban, features the return of the regular cast of children, teachers and guardians, as well as a number of new characters and creatures. This time around, a shadow is cast over Harry’s third year at Hogwarts with the news that mass-murderer Sirius Black (Gary Oldman) has escaped from his prison in Azkaban, apparently intent on finding and killing Harry.

Industrial Light & Magic vfx supervisor Bill George was challenged by Cuarón’s call to make the vfx photorealistic. Photo courtesy of ILM.

The darker material, Alfonso Cuarón's direction and vfx supervision from Roger Guyett and Tim Burke drove the creative choices on this movie. “Alfonso is a very passionate director. He just didn’t want things to look fake or effectsy. He had a philosophy that if it looks too flashy and too much like a special effect, then it cheapens it... He is such a unique director. Most directors want if as big and spectacular as we can do it. He was much more about subtlety,” reveals Industrial Light & Magic vfx supervisor Bill George. Reportedly anti-CG going into the film, Cuarón wanted to ground this film in a reality. The effects needed to be organic, driven by the magic. The CG not only had to be photorealistic, but also needed to behave more mechanically. According to Simon Stanley-Clamp, vfx supervisor for Cinesite in London, “He didn’t want a ‘Terminator-look’. That was his term for anything CG.”

To create the magic for Azkaban, five different visual effects houses supplied more than 750 vfx shots.

The Moving Picture Co. (MPC) supplied 230 visual effects shots — the highest number awarded. Their contributions include the “Grim” — a menacing photoreal CG dog, a Werewolf and a reprise of the Whomping Willow.

With a team of about 100, ILM broke 200 shots with the Quidditch game, the Dementors, the Boggart and others.

From Cinesite 167 shots made the final cut. “It felt like more because some of the shots are so long,” explains Stanley-Clamp. “Commonly, 10 seconds is your average.” The first shot the team did was a two-minute long steadi-cam shot in the Leaky Cauldron, where the wanted posters of Sirius Black are animated and there are reflections in mirrors and things.

In total, Double Negative completed around 130 shots: more than 90 on the Knight Bus sequence, 20 on the Hogwarts Express and some more miscellaneous shots that cropped up along the way, the most notable being two floating CG lolly-pop shots.