Ellen Wolff talks with Sony Imageworks Pete Travers about launching Zathura into cinematic outer space.
Columbia Pictures Zathura (opening Nov. 11) is an old-fashioned sci-fi fest, complete with a reptilian monster called Zorgon and a shiny metal robot right out of Lost In Space. It chronicles the out-of-this world events that unfold when two brothers roll the dice and play an old board game that theyve uncovered in their basement. Zathura, directed by Jon Favreau (Elf) brings to the screen another adventure from Chris Van Allsburg, author of Jumanji and The Polar Express. And Sony Pictures Imageworks, fresh from having animated the latter film, has handled more than 200 digital effects shots for this movie as well.
Imageworks vfx supervisor Pete Travers, whose credits include digital effects supervision on The Aviator, Haunted Mansion and The Matrix Reloaded, explains the creative challenge given to Sony by the films vfx supervisor Joe Bauer. The artwork in the book is very stylized, observes Travers. Its kind of like pointillism, and its a very 50s sci-fi look. That look was a very important aspect of the effects.
In addition to Sony, Bauer worked with Stan Winston Studios to create the robot suit and on-set Zorgon puppet. Then CafeFX computer-animated the Zorgon creature in the scene where it had to be nimble. Zoic tracked and composited star fields, and Digital Dimension also comped star fields and worked on integrating miniatures used in the film. Since there were hundreds of star field shots, Zathura was one of the seasons most heavily composited shows.
The Adventure Begins
Our first inkling that this is no ordinary board game comes when the little brother cant read the card that he has drawn. The older brother grabs it and reads: Meteor Shower. Take Evasive Action. The little brother asks what that means, and the big brother says, It means you have to get out of the way. All of a sudden a meteor shower blasts through the living room of the boys home. This is the first sequence that comes after the boys take a card, notes Travers, so the director wanted it to have a high level of energy.
Principal photography showed the boys running around on a practical set with meteor holes already in the floor. Imageworks matchmoved the scene to create a digital camera and then added CG meteors, smoke trails, sparks and interactive glows. The trails themselves were run using a fluid-based simulation with dynamic interaction, frequently with the actors.
The view of this chaos takes place almost entirely from the kids POV, explains Travers. The director wanted this to be up close and personal. But there were exceptions. Sometimes when youre watching a movie youre starving for establishing shots to show whats going on. And they are in there. The Saturn sequence is like that.
In the Saturn sequence, the films second major adventure, the boys discover that their house travels through space. The kids open up the door and look out onto their porch, says Travers, and theres a giant thing in the way, which turns out to be an asteroid. As the camera moves over their shoulders out into space, the planet Saturn is revealed. By the end of the sequence, you are looking at a tiny house hovering over the rings of Saturn.
The effect was composed of a background matte painting of nebulas, and stars mapped onto a semi-curved surface. Saturn, along with its orbiting asteroid belts and moons, was built in 3D. Since the planet is gaseous, with storms raging across its surface, Travers team ran fluid simulations to mimic this. Were a big Houdini house, but were also a big Maya effects house. This movie was probably right down the middle. There was a lot of Houdini for meteor smoke trails and flares but there were also lots of effects done in Maya, including the asteroid belt and Saturn. But the dust surrounding the asteroid belt was done in Houdini and rendered in our proprietary renderer Birps. It gets tricky, and you spend a lot of time making sure your glue-ware is working.
You pick and choose what will suit the shot and what the individual artist is comfortable with. Sometimes you have to pick two different packages and make sure that youve got glue-ware on the back end so you can composite everything together. Our pipeline for dealing with Houdini, either through Maya or coming back in through RenderMan or even rendering out of Houdini and then compositing is very solid.
Questions Of Character
A key character in Zathura is a giant, lumbering robot who destroys half the house while chasing after the kids. It was often played by a performer in a suit, with Imageworks matchmoving the performance in order to later add CG arms and legs. Stan Winstons guys built a number of different robots that had different capabilities, recalls Travers. In some robots, the backs opened up and rocket thrusters came out. In others, they added a saw blade to one of the armatures. But when the robot had to run around, there was no way a human could fit in its framework and actually move the arms and the legs. The robots torso is huge and the legs are skinny and the feet are big and the shoulder blades are way out. The arms themselves hang way down past the knees and theyre very thin. So what do you do?
Director Favreau actually loved it when the performer who could barely see outside the robot suit would bump into things. The robot was literally crashing into doors and falling down, Travers remembers, and Jon was saying, Perfect! because the robot was supposed to be clumsy. The advantages of doing it on set, obviously, were that Jon could see and approve the performance. And if any actors were responding to it, their reaction was perfect. Also, the robot was so big, just by walking into the room it also affected the lighting on the set dramatically. So its shadows were built into the plate. We got them for free.
Travers explains, In shots where the torso and feet are practical and were adding CG arms and legs, it got a little tricky. We had to matchmove the practical robot, but then we also had to give it to the character animators, because if we just did a straight matchmove and put in CG pelvis-to-ankles, it wouldnt necessarily be the performance that Jon wanted. A guy could fit in the robot suit, but his proportions werent anywhere near what the robots pelvis was. The robots hips were much wider than the performers. So he would do his best to keep the general relationship between the feet and the torso where Jon wanted it, and then wed have to figure out a way to fit everything in between in there. We had to put a lot of controls in there.
The Virtual Version
The process of digitally augmenting the practical robot fell to Imageworks animation team, which was lead by CG supervisors David Seager, Bob Winter and Bob Peitzman. Throughout the process, observes Travers, There was crossover point between a matchmover and a character animator, where we had to figure out the stopping point for the matchmover. There was really a fine line. Should we just continue to match the performance? Or was it time for an animator to take over and then bend the knees or the hips or whatever needed to be done to make the performance work? When you matchmove a torso and you matchmove the feet, there are only so many degrees of freedom left for moving the pelvis. Essentially, thats the definition of inverse kinematics. You keyframe the target for the kinematic chain and the kinematic chain decides how to move. What ended up was that the matchmovers did a lot of animation and the animators did a lot of matchmoving. A lot of communication was required. But when it was all done, recalls Travers, there were a lot of shots where Jon Favreau would look at it and ask us if it was the practical robot or the CG version because he couldnt tell. And thats always a good sign.
Imageworks used Maya for matchmoving models and animation, and used an MTOR Maya to RenderMan pipeline. We call it our alternative pipeline, notes Travers. The renders took a while but we ran ambient occlusion passes and reflection occlusion passes. We have the ability to render all the occlusion passes and key lighting passes in one fell swoop or we can break it down. There are pros and cons to each approach. When you have so many passes you get a gigantic node tree. Its comp bloat. As much as we talk about how expensive it is to render, if there are processors sitting idle at night, hitting the render button and having it chew through something so that its done in the morning thats free.
The robot shots in Zathura also involved what Travers called some nightmare composites. In one shot, the robot chases the boy through two doorways and he smashes both doorways. The passes of the robot were shot with motion control, but the explosions of the doors couldnt be done that way. There was no way they could time it with motion control and they had to be shot separately. So we had to kind of Frankenstein together one overriding plate and match move that to do our robot pass. The robot ended up being fully CG in the shot, but we started with a match move of what they had there. To track the exploding doors and to get them into this complex 3D move was tough.
One especially scary sequence in Zathura unfolds when the boys flying house is pulled toward a giant gravity planet called Tsouris3. Nobody has ever seen Tsouris1 or 2, jokes Travers. The house itself was shot motion control in many passes, so that the balancing of the lighting could be handled within the composite. But Tsouris3 itself required a fully digital solution, composed of flowing lava, atmospheric clouds and a large corona of solar flares that interact with the house.
Travers explains, We had to do a lot of scaling of that planet, just like we did for Saturn, to fit the planet in the shot and get the right composition. Tsouris3 is supposed to be gigantic, but we had to cheat the scale to make it work. It hurts when you youre trying to cheat something and you have a 3D camera move. If youre just looking at a planet as a backdrop, it could be 50 billion light years away. But as soon as you have a 3D camera move, the gag gets revealed.
Of course, the only way to demonstrate that Tsouris3 is a gravity planet is by showing how other objects react to it. We had a house that was constantly spewing out debris thats flying toward it. Tsouris has a giant, glowing corona with flares shooting off of it, so you get a sense that its a big thing. There is a shot where the house is screen left and the planet is screen right. Its a cheat (in terms of scale) but if youre to buy into the danger to the house, the planet had to be in the shot.
Enter The Zorgons
Just when it seems like things cant get any wilder, the Zorgon battleship arrives to attack the boys house with a harpoon and cable. The practical plate consisted of an interior house with a harpoon shot out of a pneumatic rig. The backside of the harpoon and rig were removed and replaced by a digital harpoon that emerged from the ship. The ship, designed to resemble an old ironclad, was CG, including thrusters and torpedo blasts.
That foreground ship is not alone, either. Its part of a Zorgon armada comprised of dozens of background ships. Because this attack sequence represents the films climax, it was carefully previsualized to determine the motion for the shot. The house was filmed as a miniature in multiple passes, in both the pre-destruction and post-destruction phases.
Theres some heavy duty digital stuff of the house at the end, says Travers, because there are 45 ships flying around the house and blowing it up. All of the explosions and all of the debris flying off the house shingles and big panels thats all digital. There was some practical pyro, so we had to figure out a way to get the pyro in between the miniature and our digital explosions. It got into some heavy-duty compositing. As a general rule with this kind of stuff, the power of it is in the details. It was hard to know when to stop. We just kept adding splinters and shingles. Compositing, using Sonys alternative pipeline, was done in Shake, and Travers notes that when it comes down to broadening our tool set to include Shake and MTOR whatever it takes then Im all for it.
The Final Analysis
Before a movie starts, Travers reflects, you always look at a handful of shots and think: These shot are going to be the nightmares. But by the end, there are a few shots that you werent necessarily thinking about which end up being the real nightmares. The ones that youve put a lot of effort into thinking about at the front end typically go a lot smoother, maybe because youre bracing for them!
Movies have a tremendous amount of things that you could continue to improve. And there was a time when you didnt have the capabilities to do that. But along came digital effects and now you can do anything, which is a double-edged sword. And digital intermediates are going to have more and more capabilities as time goes on. Theres a lot of Hey, lets fix that in the DI. Its both good and bad. Its great that we have the capability, but we do at a certain point have to abandon the movie, and thats difficult when these tools are sitting there. Thinking about how this situation might apply to the film he just finished, Travers laughs and says, Hey, this version of the movie could be Zathura 1.0!
Ellen Wolff is a southern California-based writer whose articles have appeared in publications such as Daily Variety, Millimeter, Animation Magazine, Video Systems and the website CreativePlanet.com. Her areas of special interest are computer animation and digital visual effects.