"Chris has an instinct for what kids like because he always seems to be aiming that way, and the action and effects have more of an edgy slant, which makes them feel like they're seeing something above them," the overall visual effects supervisor suggests. "There is also something about it that reminded me of reading your first adventure book as a kid."
Indeed, a movie inhabited by Zeus (Sean Bean), Poseidon (Kevin McKidd), Hades (Steve Coogan), Athena (Melina Kanakaredes), Medusa (Uma Thurman), a Minotaur and Hydra -- for starters -- is rich with visual possibilities and vfx challenges.
"Digital Domain really stepped up with their water and it was a great opportunity to do some creature work," Mack adds. "I was real happy with what MPC did with Hades and Luma just did fantastic work with Medusa. Uma was great to work with: she had so many ideas for how to act and behave in a way that would tie her in to the big snakes on her head. She gave herself a weight to her head movements and she would relate to the snakes and look at them, even though they're not there. It gave us a lot of cool stuff to back into in terms of the snakes interacted with her. And she had this whole notion of her relationship with them: that they were her only friends because everybody else got turned to stone.
"Pixomondo did a handful of shots but they were big ones: the Hades Underworld exterior where the boat comes out of the Hollywood sign with the city in ruins. It's a combination of 3D and 2D. In the end, it kept changing and I wound up doing a drawing on one of those dry erase boards that we did the schedules on and in about five minutes I did the city in ruins with big chasms and stuff floating in the air, and Chris really liked that. From there, they did more illustrations based on that drawing and we developed it at Pixomondo, which did previs early on and projected paintings onto the stuff."
For Digital Domain, which contributed about 350 shots, the Hydra and Fury creatures provided an animated change of pace. "We were really excited to do great character work, spending a lot of time designing and modeling Hydra and Fury, getting the look just right," offers Kelly Port, Digital Domain's visual effects supervisor. "For the Fury, we got a simple sketch from Chris Columbus, which had six wings and big teeth, but that was essentially it. Nick Lloyd was able to take over the designs for that and was able to mock it up in both 2D and 3D and get that concept look approved with Chris.
"For Hydra, we had Raul Dominguez model the Hydra, so we actually built it from a skeletal structure up with muscle system and made sure it was as anatomically correct as it could be. Of course, after it grows another set of heads, it's really a whole other character with a new set of proportions to deal with. It's a difficult creature to animate with five or 10 heads and they all have to be doing something and attacking the kids. One of the challenges of that sequence was: Why doesn't it just reach over and eat them? So we attempted to build, as Kevin Mack put it, 'a junkyard dog on a chain.' While one neck is going in one direction, trying to reach around and eat the kids, another head on the other side is trying to reach around in the opposite direction and do the same, so they pull at each other and fighting and that's why we set it so it was so difficult to get the kids."
Digital Domain implemented RenderMan's point-based lighting  into its pipeline to enhance its work on the Hydra. The studio also utilized a lot of animated displacement maps for Hydra when it came to refinements for muscle and skin sims. Digital Domain additionally improved its fire pipeline using Houdini for the Hydra sequence. While locked off elements were shot in Vancouver, digital fire was required for the extra lag when necks moved in space and rotated.
Meanwhile, Luma embraced Medusa with open arms, so to speak, under the supervision of Vincent Cirelli. In fact, the challenge was like directing 70 extras on set with a dynamics layer on top of the animation rig to ensure free-style movement and interaction. Luma devised a rig to add 3D scales that could be matched to the performance by the animators, complete with "a scaly outer shell that fans out naturally with each wriggle."
For Poseidon, Luma used RealFlow  and customized dynamics rigs to dissolve the actors' body into and out of a rushing torrent of water. Luma also had to create the effect of Poseidon emerging from his underwater kingdom. For this, the studio created very precise matchmove geometry to track to the actors face, and then we used this to run RealFlow simulations to create water sheeting off his skin.
MPC Vancouver, under the supervision of Guillaume Rocheron provided 160 shots, including the creation of Hades, the 12-foot-tall fire demon and simulating a fiery inferno. ; For Hades' facial performance capture, MPC used the Mova Contour Reality Capture system and integrated the data taken into MPC's in-house motion blending tools and motion clips manager to allow the artists to mix and tweak different dialogue and expression takes according to the requirements of the shots.
Hades was joined by the Minotaur, a huge furry and athletic beast that Percy fights, and the Hellhounds, who are half -dog, half hyena; both used MPC's Furtility  fur solution. As with Hades, MPC modeled, textured and rigged the creatures using custom muscle and skin deformation solutions. Photoreal fire simulations for Hades and the giant fire inferno with hundreds of CG fire-like creatures called the Lost Souls entailed some bar-raising work. They were computed at a voxel size below 1mm and then plugged into MPC's rendering system to generate accurate illumination onto the character.
"Our FX team pushed the fire simulations to a much higher resolution than we've done previously to ensure details were contributing to the motion and not only added as a post-process,"
Bill Desowitz is Senior Editor of AWN & VFXWorld.