In Wrath of the Titans, the sequel to 2010's Clash, Perseus (Sam Worthington), son of Zeus, must rescue his father whose power is being drained in order to awaken Kronos - Zeus' own father imprisoned in the Underworld. The Jonathan Liebesman film, a 3D stereo-converted show, once again features a bevy of mythical gods and Titans - from the devastating Kronos, to the deadly Chimera and Makhai and the giant Cyclopes. In this article we take a look at the work of Nvizage, MPC, Framestore and Method Studios, who, under overall VFX supervisor Nick Davis, brought many of the creatures and visual effects of Wrath to life.

- Above: see MPC's breakdown of their creature work for the film.

Previs'ing the creatures

Nvizage previs for the Chimera attack.
Previs for the Cyclops by Nvizage.

Nvizage produced over 300 shots for the Chimera and Cyclops attacks, as well as other scenes featuring a labyrinth, the armillary sphere and the Underworld prison of Tartarus. Nvizage replicated the Panavision camera system used on the film, lens choices and camera rigs in forming its previs. The studio also created diagrams for the heads of departments once previs had been approved.

"Nvizage started work on Wrath of the Titans, working with Production Designer Charlie Wood based out at Longcross Studios," says Nvizage CG supervisor Martin Chamney. "Within the art department we helped design the Labyrinth set and experiment with various motion studies and gags that could feature in the Labyrinth. Previs work continued with the creature action sequences, under the direction of VFX supervisor Nick Davis. Using construction drawings and concept illustrations from the art department, Nvizage organized virtual environments from the combination of practical locations and digital set extensions."

A virtual camera system (VCS) at Longcross and Shepperton Studios within a 20 foot volume was employed to facilitate creature previs. "This is essentially an optical motion capture system that facilitates soft body mo-cap for bi-ped motions and a rigid body capture that drives the position and orientation of the VCS," explains Chamney. "Once any scene layout was setup anyone could take control of the virtual camera and start exploring the fully textured virtual environment and begin figuring out shots. The VCS helped director Johnathan Liebesman choreograph key fight sequences within the movie, including Perseus' epic battles with the Chimera and the Cyclops."

"The director wanted the camera moves to feel visceral, fast-paced, handheld, similar to the action scenes in the Bourne films," adds Chamney. "This was all achieved with the VCS, which was perfect for creating this kind of realism in our virtual scenes. Some of the shots were very long, and the challenge was to tell the story with exciting camera work yet retain a plausible possibility of being photographed for real."

fxinsider members can also read about the visual effects work by Nvizible (a sister company to Nvizage) for the armillary sphere scene in the film.

The Chimera

A rhinoceros-sized mythological creature from Greek history, the Chimera was realized with two heads - one a goat and the other a lion - and a snake-like tail, by MPC. The creature, which emits liquid from the lion's head and then produces a stream of fire from the goat's head, emerges from the earth to wreak havoc on Perseus' village. "We more or less took the body of a lion, but beefed and bulked it up, and played with the length of his limbs to make it look like he could actually support the two heads," explains MPC visual effects supervisor Gary Brozenich. "That was the big engineering question - how would it move with all of that weight hanging off the front of him? So we did some animation studies, trying to figure out the correct proportions."

Perseus battles the Chimera. Click to enlarge.

The village sequence was shot on a dressed outdoor setting in Tenerife, one that allowed for a frenetic and close-in camera style to be employed when the Chimera attacks. "With the size of the Chimera," says Brozenich, "there were actually quite tight narrow corridors that were deliberately put in place on set so that he would be forced to confront people, pick them up, throw them, stab them and rip them apart. So with that in mind, we went in there with discussions about building shadow-casting objects and having significant stuffies and proxies on set, but really what it came down to with the speed of filming we needed to do and the amount of interaction and 150 extras - there wasn't going to be much time to deal with that stuff."

With limited time, Brozenich sat down with the stunt coordinator Paul Jennings and special effects supervisor Chris Corbould and blocked out the moves the Chimera would have to take. Previs from Nvizage was also used to help establish the moves. "A lot of the route the Chimera took was mapped us by us in conjunction with the special effects guys," notes Brozenich. "They had a lot of smashed up walls that would be pre-smashed or built to explode, pyro explosions and flamethrowers and a lot of squib hits and dust - they're called 'shitkickers' - that would kick up dust and debris along the route."

"We'd also do a series of clean takes," adds Brozenich. "I was concerned it would tie us in to too much timing - that the interaction might penetrate the Chimera or go through people in an unnatural way - but nine out of ten times we ended up going for the original special effects pass on it, because it really suited Jonathan's style - grit, dirt, debris. For us to add all that back in was never going to be as convincing as when we shot it for real."

Watch Perseus take on the Chimera.

In terms of design, MPC looked to diseased animals as reference, since the Chimera was to feature mangy hair and many scars and blisters. "We wanted to make sure this thing looked like it had been through the wars and if you looked at it, you'd think, 'Oh shit, I'm dead'," says Brozenich. "We were never going to make it so that if you looked at it you'd be sick, but we wanted to get you pretty close to that. And it explodes out of the earth too, so it had to be dirty."

The Chimera was sculpted in ZBrush and modeled in Maya, before going through MPC's textural displacement stage and shading pipeline. "What made the biggest difference for us was our fur system - Furtility - which has been developing since 10,000 B.C. when we did the mammoths. We drove the color of the fur from the tip to the root of each individual hair if we needed to. We could also have different bits of material hanging within the hair too. So we had a debris pass that would be clumped into the fur and drag underneath and behind it, and would interact. We could do effects passes and use those as rigid body interactions with the fur. If there was an explosion on set or if he had to go through a wall, we would have an effects object going with him, which meant that the broken, rocks or debris could interact with the fur."

In one shot the Chimera explodes a stream of fire against Perseus who has only a wooden door as protection. "For that," recalls Brozenich, "the SFX guys had flamethrowers on standby, but obviously no-one was going to be happy with them firing those on Sam. So we replaced what would have been the flame with a huge bank of lights on a dial system. Sam had a practical door that we put tracking markers on, and had witness cameras on it to rotomatte it."

Worthington mocked reacting to the flames, and Brozenich then shot clean passes of flamethrower flames. Back at MPC, artists matchmoved the shot, rotomating both Sam and the door completely. "We built a CG proxy door which was textured to be burnt that we rendered out on top of the live action door," says Brozenich. "We did a sim of the fire in Scaline's Flowline that started to blow the door apart, so we had the CG door disintegrating underneath the flame. That was then rendered through RenderMan and the flames partly in mental ray. Most of the embers were 2D elements - we then added a lot more stuff coming off the door and debris. We had to build up some light interaction on Sam - there was a lot there but because it was shot in blistering sunlight in Tenerife - the amount of additional light you could get on him that was stronger than the sun was limited. Smoke elements were mostly 2D. So it was quite a big combination of practical and CG."

Watch behind the scenes of the Chimera chase through Perseus' village.

In a shot running over a minute in length, Perseus pursues the Chimera along the village rooftops before jumping on its back. "It starts off with a good look at the Chimera," says Brozenich. "He picks up a digi-double human, plays with him like a cat with a toy, throws him off camera, turns and blows a flame right at camera. Perseus then turns and starts to pursue the creature, and you pick up on the Chimera at four different points. He keeps re-appearing with someone new in his mouth that he's ripping up or he's blowing flames. Perseus then runs up on top of the roof and jumps on the creature, before stabbing it."

"A lot of technical previs was done on the shots for production, mainly for the cable cam," adds Brozenich. It could be repeated in its performance, and the head can be recorded, although you have to manually operate this. At a point as he leaps, we do a digi takeover and its a digital Sam, who then jumps onto the CG creature's back and stabs him in head. Then we do a wipe with one of the Chimera's heads to bring back in a live action plate - a separate plate shot on a ride rig shot on a separate location later on that day. Then a wing wipe comes over to wipe back to a CG Sam who is holding on for his life. The Chimera turns and flips him back over and we wipe with another wing to reveal a third plate of a stuntman who is thrown off the ride rig and rolls down the hill."

Having inflicted a near-fatal blow that causes the Chimera to spill inflammable liquid, Perseus throws a chain -  an MPC rigid body object that pushed and pulled the CG groom - around its neck and chokes the beast, before the mix of leaking fuel heat haze causes ignition. "We were going to do a burning groom where it went from A to B and burned over time," says Brozenich, "but the action happened so fast in the end - over two shots - that we found that we could just do a burn groom and a non-burn groom and render them both. With the combination of live action and CG fire we would just visually blend between the two with mattes and comp."

The Cyclopes

Perseus' ultimate quest is to form the Spear of Triam, a weapon that can defeat Kronos and the combination of Zeus’ Thunderbolt, Hades' Pitchfork, and Poseidon’s Trident. His search leads him and his party to Hephaestus's island. Here they are attacked by three giant Cyclopes - digital creations by Framestore - in a forest before convincing them to help Perseus' cause.

Cyclops by Framestore.

Framestore visual effects supervisor Jonathan Fawkner oversaw the Cyclopes creatures, essentially a father cyclops and two sons. Animation supervisor Paul Chung conducted some early research into how the cyclopes would behave. "The brief from the director was not to have slow-moving lumbering giants," says Chung. "They had to be a little more intelligent. So I did some research how big guys move, but if each of the cyclops looked the same it would be boring. So we created these back stories for them - the younger one we thought would be a little more hot-headed as a fit cyclops - maybe he would make more mistakes. The older brother would come to his rescue, but because he was overweight he would be out of breath and panting and not very energetic."

After reviewing previs and developing storyboards and some initial blocking, Framestore also embarked on incorporating early motion capture prior to the actual shoot. "We'd been out to the set and we already had a Lidar scan of the set, shot in Dawkins, south of London," says Fawkner. "That meant on set we had some pre-canned animation that we were able to show what we had done, and use that to inform Sam Worthington and the director as to how fast the cyclops was moving."

After principal photography, Framestore then took every shot from the long cut, tracked them and built a CG version with virtual cameras. "Then we lined up a mocap set-up so that we could literally drop our cyclops into the plate," says Fawkner. "It worked incredibly well. The cyclops would go behind trees and in front of trees and we could line up the prop trees to get the right place. I then directed the cyclops performance in this mocap performance - sometimes up to 20 takes. After a week of mocap we got enough for 50 cyclops shots."

The motion capture performer was ex-England rugby player Martin Bayfield who had actually been standing in for Hagrid in the Harry Potter series. On a motion capture stage, Bayfield carried out the Cyclops actions via an optical system, with witness cameras set up also to aid animation down the track. After mocap, Framestore provided editorial with live comp'd Cyclopes into the filmed plates. Says Fawkner: "So they chose takes which was a fantastic way to get someone to sign-off on animation and blocking. We would wait for them to make their selects, then they re-cut and off we went - we would put the higher-res bodies onto the motion capture. It was a really nice way around and I was glad they really stuck to the motion capture."

Watch a featurette on the Cyclops.

In terms of animation, Framestore relied on a new method to re-target the mocap to the giant Cyclopes. "We had been experimenting with various solvers," explains CG supervisor Mark Wilson, "taking the raw mocap data straight from the plate, and putting that onto your character rig. We came across the IKinema software - a full body IK system. It allows us to solve the mocap without stretching any joints or forcefully squeezing things to fit. It does a really good job of solving the initial mocap to our base rig."

A significant challenge for the animators was creating human-like expressions from a creature with one eye. "For example," notes Chung, "when we get angry, our eyebrows go down in the middle and form a V-shape, and then when you're upset, they go the other way. But when you have one eyebrow you won't be able to create the same V-shape. So we developed some asymmetry and wrinkles to move around." Animators also had to adhere to a made-up language to enable the Cyclopes to talk, although most of the remnants of the talking do not appear in the final film.

Looking to adopt a new raytracing approach in Framestore's rendering pipeline, Fawkner set CG supe Mark Wilson a challenge before embarking on the final Cyclopes shots. "I said, 'Can you go out into the mews behind the office, photograph and texture it, divide out all the lighting from the HDRI and set that up so you can raytrace the Cyclops and stick him in the yard outside our office? If you can make that work, raytracing that, I'll make sure we've got all of the right reference for doing it in the forest. And he did."

"Mark said RenderMan v16 was not out yet but was going to have full raytracing," adds Fawkner. "And we were working in Arnold as well, but our skin shading was RenderMan. So PRman was in alpha, but we took the plunge. I wanted the lighting to be physically based and allow me to design the lighting, and worry about the technical veracity."

Click here to read fxguide's Art of Rendering article, which includes detailed discussion of both RenderMan and Arnold.

On set, Lidar scans and light surveys had been taken. "We surveyed all of the lights for every take," says Fawkner. "So when it came to setting up all of the lights, I photographed each of them, and had HDR source photography. Then we put them onto geometry which illuminated the Lidar of the set. The results were really pleasing and we got really convincing stuff early on. We based our lighting model on Harry Potter 7 for Dobby and Kreacher, but this time with full ray tracing. We had to re-write the scatter, hair scattering. We got noise free, flicker free hair all over his body. The moral of the story is we got really good early stuff, even if it wasn't quite right initially."

"The cyclops was incredibly demanding as a character to solve," says Wilson. "It's pretty much a photoreal CG human. He's not wearing a huge amount of clothes so you really see most of his body. We took a volume mesh approach - the volume of the cyclops was modeled underneath him and on one side it's attached to his bones with a rigid attachment. Then the mass is given a kind of stiffness and tension is given to match what his muscles are doing and there's complex mapping internally for all the anatomy. The rig sets up the fleshy bits or muscly parts and passes the data down the pipe. We had to sim all the anatomy, all the way down to the peach fuzz on the face. His face was triggering dynamic displacements and his skin was simulated to slide over the displacements and feel like it was traveling over organs underneath. Then there was muscle sim, fat jiggle sim and skin slide."

The shots were composited in Nuke, with an early challenge having to match to the on-set mist and smoke. However, an even great challenge was awaiting. "Half-way through our post period," recalls Fawkner, "the director said, 'Wouldn't it be nice to color-time the plates and bathe them in sunlight and not just in real fog?' So we were at a stage where we were getting really great results with the reference material from the plates, and then they wanted sunlight. So we dropped in beams of sunlight that would interact with the cyclops and would also have to hit the ground. We made the decision early on that no human characters were going to be sunlit and that they would neatly dance through the rays of lights without getting hit, so we wouldn't have to alter the people in the plate - we could alter the set, that was fine, but not the people. We had volumetric atmosphere renders coming out of mental ray, and Arnold towards the end, and chucking them into RenderMan scenes and comp'ing them all up."

Another view of Framestore's Cyclops work.

Compositing supervisor Chris Zeh's team also added in a multitude of effects - dirt, leaves, footfalls - to tie the Cyclopes into the plates. "They shot some things on set which are always quite good," says Zeh. "They'd shoot a hero event like a tree falling over. But to get his footfalls right we used a lot of 3D effects of little twigs and leaves and dust - there were a significant amount of live action elements as well."

Another challenge for the compers was the close-to-camera nature of the shots. "There are two shots where a cyclops' face is full-screen," comments Zeh. "With shots like that, it always involves tweaking in small detail. Getting an eye to look right is always a challenge. You sit there and noodle for hours and days to get the refraction through the lens and the caustics in the iris and this and that working. You have effects, like the light that refracts through the lens that almost ends up on the other side of the eyeball illuminating it from the other side. So we rendered a good deal of it - they built the eye to a high detail and because we were raytracing a lot of the detail could be achieved in the render. Then you look at it close up and you're not quite happy with it - and eventually you end up tracking in little illuminations or lines or removing things are little hard, or ramping up the spec to make it look wetter, and making sure the eyelashes aren't too thick. It sounds like small things but they can make quite a bit of difference."

fxinsider memebers can read more here about Framestore's visual effects work for Wrath on the later Labyrinth sequence.


Kronos in the Underworld.

Imprisoned by Zeus and Hades in the Underworld, Kronos is brought to life when Zeus is captured by Hades and Ares, and made to transfer his energy to the giant god. In his slumbering state, Kronos is perched almost within the rock of the Underworld. Method Studios, through its LA and UK offices, created shots of Kronos beginning to break free, as well as establishing scenes outside the prison Tartarus, shots of Zeus' power being drained to awaken Kronos and a transition to the battlefield above.

A fully CG Kronos made out of 7,000 pieces was combined with smoke, atmospherics, explosions, lava, embers, pyroclastic and volumetric effects and falling rocks and debris to depict his rising. "In particular," says Method visual effects supervisor Olivier Dumont, "we had a lot of lava at different scales - it goes out of Zeus' veins, then down to a bridge and then reaches Kronos. We tried to mix simulation with a layer of control to try and increase and slow down the speed of the lava."

Method created the lava using a combination of Maya (for character animation) and Houdini (to produce the lava cracks in Kronos). "For his cracks, you cannot just have a texture projected on Kronos and then have him moving because it's going to stretch and it won't look right," explains Dumont. "He didn't move that much, so we were concentrating on getting the main action readable for the audience. There is a big shot where he is taking his hand out of the rock and looking at it and groaning and frowning. We tried to get something interesting in the details for his eyes or in the background - he's flaking, there is smoke coming out of him."

Watch a breakdown of Method's visual effects work for Wrath of the Titans.

For the rock falls inside the Underworld, and from Kronos as the entire environment crumbles, Method looked to glacier reference. "We developed some procedural systems to have good destructions in Houdini," says Dumont. "We looked at reference - when it's that big - of how a mountain could fall. We looked at how a glacier falls - because it's so huge, everything seems to be connected - big bits falling on themselves until there are so many small bits that it looks like a river."

"You take a block and first of all you fracture it once and then again and again," adds Dumont. "Big pieces collect on themselves and that continues to happen to get that glacier look. We would draw the cracks, then transfer that to maps in Houdini, and the tool we had was like building blocks on these maps. When it gets small enough they would break into dust and particles. We also had smoke and dust elements to mesh everything together."

Once risen, Kronos confronts his sons by exploding out of the earth in shots completed by MPC, but he is ultimately destroyed by Perseus via the Spear of Triam. "For these shots," says MPC's Gary Brozenich, "we wanted Kronos to have a timeless quality - a classical Greek artistic look. There were two sculptures I wanted to include - Auguste Rodin did a sculpt of Honoré de Balzac, a French writer from the 19th century, that was beautiful but very rough. It looked like it had been hacked out of the roughest rock you can imagine. But it had a big presence and big arms and hands. Then there was also Michelangelo's unfinished slaves. They're not as refined as you would imagine his work to be, but they have an incredible classic look and beauty. This is something we wanted to get into Kronos - that he was made from the earth."

Perseus, atop Pegasus, fights Kronos.

With these design principles in mind, MPC exaggerated some of Kronos' proportions with longer than usual arms and broader shoulders. They also added chunks of rocks that hang off the God's head, almost like a crown, but were broken and shattered. To help realize Kronos' movement, artists at MPC painted a colleague with wet clay. "He was quite a muscly guy to match Kronos," says  Brozenich. "We let that dry and cool and they filmed him with an overcranked speed doing really slow movements, and also photographed him with a digital camera from different angles so you could see what would happen if you took a human made from something earthy - how would the cracks form?  That was a huge help and made a huge foundation of what made him in the end."

Using Maya and ZBrush, artists then set about a 'massive' modeling project, with one the key features being Kronos' plates that move and shift around on him to make him a bubbling, moving surface, with a cooled shell that sat on top. "Also, from an effects standpoint," adds Brozenich, "we at MPC have never faced anything as difficult as Kronos. People know what volcanoes look like - what a pyroclastic plume looks like. By a great fortune, and misfortune for others, at the time we were diving into this, the volcano in Chile happened. There was also one that happened in Indonesia, and another in Iceland. So we were inundated with material, especially in HD, to use for reference. There was one particular moment from Chile that Jonathan latched onto - a dusk shot where everything had gone dark and there was a lot of visible lightning within it. It was a recognizable cloud but looked more fierce."

"Kronos also has lava constantly dripping off him," notes Brozenich. "There were platelets simulated against each other and dropping little rock simulations off of them. He's got the lava core, which was treated more as a shader than effects simulation. He's got body trails, interactive plume - major pyroclastics off his back and head - the most creatively difficult to get right." The effects team at MPC used Scanline's Flowline to create the lava spills and flows and explosions, and then the studio's rigid-body solver PAPI and finite element tool Kali for the shattering earth in certain shots - along with many layers of real and CG dust elements.

Kronos concept art.

"One thing we did with Kali," continues Brozenich, "is that what we found is that you can get fantastic simulations from it but we didn't always want to render the objects. So what we would do is have Kronos destroying the earth and ripping up the ground with a Kali simulation - and then we'd use that to drive Flowline simulations of lava trails or smoke trails coming off the Kali objects (which we wouldn't render). We'd just use that to drive that through any pyroclastic simulation that was done. It just gave very small detailed events that would happen that we wouldn't have gotten any other way. The other thing that came out of that was the volumetric rendering - we hadn't had a proper shader in place for before - we had a team working on that for 3 or 4 months."

Perseus, possessing the Spear and riding astride Pegasus, is able to destroy Kronos from within the creature. The winged horse Pegasus, also seen in the first film, was an asset MPC re-rigged and re-adapted for the sequel, although a similar approach to applying tracking markers to a real horse was employed on set. "We also re-groomed the horse to be a little more rough and rugged and so it felt more natural," says Brozenich. "The wings were done through our fur tool Furtility. They had guide curves that would run down the horse, and then each of the feathers is spawned off the guide curve and as an individually groomed element. They were individually instanced feathers. You could read each individual quill up close, then when we got wider they would be broken down into even smaller groups of feathers that had a lot less detail."

The Makhai

Makhai concept art.

Before Kronos awakens, he spawns the Makhai from lava catapulted at the battlefield. MPC created the human-like warriors which had two torsos and heads and six arms (the creatures also appear in the Underworld in shots shared with Method Studios). "The Makhai started its life with a single torso and multiple arms, a little bit more like an arachnid," says Brozenich. "But after talking with Jonathan, he was keen to do something crazy and make them into something welded from the souls of dead warriors. So he came up with this idea of having two torsos - one that would come out of his back almost as a surprise attack."

For reference, MPC looked to burn victims, and then replicated a 'half-baked out of lava and cooled exterior' appearance. "It was a combo of flesh and rock," says Brozenich. "It had to be horrific and seem born from Kronos. The Makhai then enter the battlefield in meteor-like explosions. They had to arrive but not come in elegantly - they enter out of control - they hit the ground and explode out of a ball of fire. And very quickly they orient themselves and figure out where they going - but they only have one purpose as killing machines."

Before filming, stunt performers rehearsed pre-choreographed fights dressed in a green gimp suit on stilts. "But we knew we couldn't have a guy on stilts on set because he would always be in a different place than the Makhai would be," comments Brozenich. "So we figured out a way for the stunties to rehearse it with pre-choreographed fights figured out. They had a combo of jerk rigs, quad bike pulls, and guys doing stunt performances - getting picked up, dragged and hitting spikes - almost always without someone else hitting them. Then our animation supe worked with them and video'd them and put them back into the pre-rehearsed fights from the empty stage - all pre-thought out."

Zeus versus Makhai.

On set, actors referenced the taped fights and previs and battled mostly against nothing, although occasionally with stand-ins for the Makhai. MPC then applied its traditional modeling/rigging/animation pipeline - albeit with adaptions for the double-torsos - to create the characters. Like Kronos, the Makhai, were placed into a large 3D environment for the battle - actually a combination of plates shot in Tiede National Park in Tenerife and a location in south Wales. "From an effects standpoint," recalls Brozenich, "we at MPC have never faced anything as difficult as that whole sequence with Kronos and the Makhai."

All images copyright 2012 Warner Bros Pictures.

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