Percy Jackson & The Olympians: The Lightning Thief is the latest in a long list of imaginative films by director Chris Columbus. The Lightning Thief is the screen debut of the award winning series of novels written by Rick Riordan. In order to create the fantastic menagerie of gods, demigods and monsters, Columbus turned to Luma Pictures ( X-Men Origins: Wolverine, Book of Eli , Harry Potter and the Half-Blood Prince, Pirates of the Caribbean: At World's End, Hancock, Apocalypto... ), acclaimed Visual Effects Supervisor Kevin Mack, who is well versed at bringing this kind of tale to life for big screen audiences.

The project was quite an undertaking and when it came time to parcel out the huge number of CG creatures and effects needed to make this film a reality, Columbus and Mack partnered up with Luma Pictures to tackle two of the most challenging characters in the Film, Medusa and Poseidon, a.k.a. “One of the Big Three"

 

Bringing Medusa and Poseidon to life

In bringing Medusa to life, the seasoned crew at Luma, helmed by Executive Visual Effect Supervisor Payam Shohadai and navigated by Visual Effects Supervisor, Vincent Cirelli set about to conquer the daunting task of turning the lovely Uma Thurman into the beguiling monster that turns flesh to stone with a mere glance. “Turning Uma's hair into a roiling mass of over 70 snakes is no job for the squeamish,” recounts Vince Cirelli. “The challenge was to not only seamlessly integrate these snakes into Uma Thurman's hair line, but also to give them each a personality,” comments Animation Supervisor Raphael Pimentel.

There were several shots in which the actress is in a battle with the hero's of the story and her performance is so dynamic that the team at Luma had to create equally dynamic animation to match. “It was like directing 70 + extras on set, each snake reacted to the environment, the actors in the shot and with each other.” Luma designed the effect so that the snakes were Medusa's all seeing eyes, reacting to events before she new about them. In one major shot, we are close up for over 700 frames of individually animated CG snakes.” To make Uma's character really slither on screen, the team started off by creating a dynamics layer over top of the animation rig in order to ensure that whatever the performance called for, the snakes could move freely without running into each other. The result is a seamless performance of actor and digital prosthetic that really sells the story of the Gorgon priestess.

“One of the great things about working with really well trained actors is that even if they are acting against a green screen or simply imagining their CG add ons, they can still bring the feeling home to the audience,” notes VFX Producer Steve Griffith. Each of the 70 + snakes on Medusa's head has a unique patterning and scale design and the larger snakes have an elaborate system of 3D scales that really sell the reptile look. “We devised a rig that allowed us to add 3D scales that could be matched to the performance by the animators,” remarks CG Supervisor Richard Sutherland. “The result is not just a bunch of bending tubes, but a scaly outer shell that fans out naturally with each wriggle”. “Uma Thurman provided us with a lot of material to work with; she really visualized the motion of her CG character and added the perfect amount of weight to her performance to bring it to life,” adds Griffith.

What would an on screen incarnation of Medusa would be without the classic “flesh to stone” effect that she is so (in)famous for. “To create this signature effect Medusa has on her victims, we wanted to stay away from the standard animated texture reveal of stone underneath the skin and come up with something unique for the audience,” Vince Cirelli explains. “What Chris and Kevin wanted was something more like a lakebed drying out in a time-lapse sequence, taking place in real time”. The result is a perfectly matched digital double whose surface is composed of tiny textured geometry flakes. “The skin transformation is driven by hundreds of thousands of particles, created in Houdini and animated over the surface of the woman's body. As the particles pour out from the emitters, instanced geometry flakes turn outwards to create a unified surface,” adds Sutherland. The end result is a dynamically evolving effect where the actors’ life force seems to dry out right before our eyes.

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