OZ the Great and Powerful

Thu 14th Mar 2013, by Paul Hellard | Tutorial

CGSociety :: Production Focus

18 March 2013, by Paul Hellard

Imageworks’ Scott Stokdyk got together with Sam Raimi and Robert Stromberg and a massive multi-studio crew of talented artists to put this Wonderland-inspired, Wizard of OZ-type screenplay classic into production. Working with crew from Imageworks, Luma Pictures as well as other smaller studios like Evil Eye Pictures, the challenge was on to create some fantastical environments, and generate colorful fiery effects.


There was a completely CG monkey, some incredibly intense tornado and storm effects, a living, breathing little porcelain doll called the China Girl, and a spinning turbine of a witch with homage to the Tassie devil character in its midst.


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China Girl

But, the China Girl wasn’t a typical CG creation. “When we were on set, we had a marionette artist there, Phillip Huber, an incredibly talented master puppeteer who’d been doing the craft for 40 years,” explains Overall Lead VFX Supervisor Scott Stokdyk, whose history goes back almost as far, in film effects. “Huber worked on the intro to Being John Malkovich. As we were filming on set, we’d shoot whoever was interacting with the China Girl, Phillip would be in a blue suit, holding the puppet. That gave a really good interaction between the lead actor and whatever became the CG recreation of the China Girl.” This became the perfect eye-line reference for the lead, James Franco, lighting reference, and performance reference for everyone else. The limitations of this real puppet gave the animation director Troy Saliba and his team inspiration. They worked from the puppet performance and worked within those self imposed restrictions. “Of course, with a CG rigged character, you can do whatever you like, but using a real puppet restricts the performance just enough that it continues to look correct for a puppet and doesn’t over-perform,” adds Stokdyk.


The final rendition of the China Girl was almost exclusively CG. There was always an ambition to use at least some of the real puppet, especially the dress. But the puppet’s dress would require at least 20 wires to preserve the flow, and then painting them out would have been a nightmare,” explains Stokdyk. “When we first introduce the China Girl, she’s kinda hidden behind a table, so there’s the real puppet there.”


The Tornado scene starts in the circus in Kansas. Imageworks sent a photographer storm chasing in Tornado Alley in the heart of the country to gather assets to study. Roger Hill is a ‘storm-chasing’ expert and showed the guys what the supercell cloud formation looks like just before a tornado drop. “Back in the studio, we built up these moving clouds, and then handed over to Luma Pictures, after their great work on the clouds in the Thor production,” Stokdyk continues. “Luma Pictures added dynamics and the funnel, while using some of the same clouds we generated. Imageworks generated a thick cloud, rendered from the kinds of images brought back from the storm chase that Sam [Raimi] ended up selecting. This was a fairly dense particulate and debris matter in there.”

On all levels, OZ the Great and Powerful was designed as a 3D movie. So, throughout the movie, Imageworks was concerned with filling the volume with density in the 25 tornadoes required. Rather than having a soft downy texture to the cloud, Stokdyk was after a granular, dusty detail in the mix.


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Vincent Cirelli from Luma Pictures talks about his work with his crew using Houdini to composite a very convincing storm or two. The base simulations, both outside the storm and inside the storm, were executed the same way but then the amount of layers were different. An incredibly dense data set is required the render the resolutions inside the storm. “Scott [Stokdyk] wanted us to gather as much detail as possible. Fill the void with very, very fine particulate, like sand debris as well as fluid,” says Cirelli. These massive datasets had to be moved through partitions with multiple iterations, so they could be art directed. Controlling a storm, but allowing the movement to look totally random. The Luma Pictures team started all the way back in Previz, in a system the effects team built for the job. “Oftentimes it is strange to have animators playing with things that effects artists build, but it was a new way to move art directed assets through this pipeline procedure. Like velocity, overall gross rotation speeds, and ‘per’ [per container speeds]. A bit like riggers building a character, the effects artists built a tornado and the animators could control that tornado, a piece at a time, like a character rig.”

The Luma team wanted to show the Imageworks supervisors what a good representation of what these tornadoes would look like, without having to run a full simulation. “If you’re trying to tell a story, sometimes the most natural, realistic result is not the result that you want,” explains Cirelli, from the Melbourne studio of Luma Pictures. “If the event was real, certain things relevant to the story could happen too quickly for the audience to register them. Each segment was timed out to allow the elements to be told in a story. From that point, the rig was driving the base simulation. The tornado was comprised of hero debris, and we had a vast library of broken planks and fences, and mid-ground and background collisions were simulation based but the foreground elements were animated. Rigid body simulations with destruction of some elements and randomised the simulations so it looks similar but and it is instanced over itself quite a few times to add the density that we need in the particulate.”


A couple of years ago Luma thought they could use the services of the programmer who invented the solver for Fume FX into 3ds Max. John Cassella from Luma Pictures and Pál Mezei, who worked at Digic Pictures at the time, collaborated with Sitni Sati on porting FumeFX to Maya. While Luma Pictures is a Maya to Arnold to NUKE facility, by Cirelli’s reckoning, using this solver with all the forces within Maya would be exactly what they needed. By porting Fume FX into Maya, Luma were able to get really highly detailed simulation inside Maya. “When rendering in stereo, with all the debris passes, fluids, with different motion blur amounts and lighting, there was a lot of early partitioning and all of this was brought together over a long period to create the tornadoes,” Cirelli describes.

The landscapes and environments, small creatures and quirky animals are strangely and quite gleefully familiar. Imageworks used as many wonderful artists in from the crew of Tim Burton’s Alice in Wonderland as they could. The result is pure delight. “It all started from the mind of Robert Stromberg, the production designer,” says Stokdyk. “Working on Alice and as well as Avatar, you can feel feel that architecture from Alice, in OZ. I had a chat with Robert very early on and decided on a fantastical land, filled with CG. The backbone of this was that we were going to build as many sets as possible, and then build onto and into them. In Alice, they were working on a lot more restricted stage space, so a lot more went virtual, whereas we wanted an art directed large stage look. We were basing the look of these sets on the descriptions set out in the original books, dressed on set, like a stage, around the actors.”


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Francisco De Jesus, an Imageworks VFX Supervisor on the production, was in charge of some specific effects sequences, describes the powers in context. “Each of the witch’s magic powers is unique. She flies in a kind of soap bubble with an irridescence to it,” he says. “This is a giant silk bubble, if you will. This surrounds her kingdom and keeps evil witches away.”

The theme of the ‘Birth of the Witch’ seems to be a recurring theme with Sami Raimi. In this instance there was the tornado involved in how the birth of the witch was created. Glenda the good witch’s kingdom is protected by the ‘Shimmering Wall’ but now it is under attack.


Magnus Wrenninge was an Effects Lead on the show and one of his specialties has always been fluid dynamics. There was a need to switch from realistic flames to more ‘magical ones’ and most of the effects was done through Houdini. There was a large visual element to the tornado that kept some of the people to approach the flames and the actor was on a rotating base, which became the platform for her performance.

The good witch invokes a full color world, whereas the dark witch is surrounded with smoke, ash, sparks and fire. “I was trying to come up with something that would tie in with the themed effects throughout the movie,” Stokdyk explains. “You may have seen a natural effect where plumes of fire twist into tornadoes during bushfires. This was adopted for the dark witch as a combination of fire, ember and smoke. This tied into the tornado that brought OZ to the Land of OZ, as well as tying into the dark witch’s fiery, elemental magical powers.”

Imageworks first of all prevized the entire sequence, shot a background on set, and then shot a separate element of the witch over blue-screen in an animation performance, introduced a CG version of her going to specific poses. Magnus went in and drove a smoke simulation, filling in the volume of the animated witch. Around that he added layer upon layer of fire, embers and smoke. Obscuring her and revealing her with hand drawn animation and blue-screen of our dark witch. “At the end of the day, the compositor was carving out, revealing and obscuring the witch on a frame by frame basis,” says Stokdyk. “There’s a lot of Art Direction in the visual effects of this movie.”

Francisco De Jesus mentions that in the the previz and through into the final render of the tornado, swears there are glimpses of the ‘Tasmanian Devil’, with limbs reaching out of the vortex as the Dark Witch is generated.



Old World Hollywood

Stokdyk, Stromberg, the DP Peter Deming, and Sam Raimi came to realise early on that these big art-designed sets and environments were now part of the American psyche, United States political history, and Hollywood’s colorful answer to the dust-bowl depression in the 20s and 30s of last century. The original story was recreated on stage, then made into the film with Judy Garland, using all practical effects of course, with huge matte painted backings, and big casts of extras. Now with the advent of digital matte painting, full extended 3D, digital CG effects, Imageworks has recreated that magic in this memorable twist of the original story.



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