Charlie's Angels 2

A 'Full Throttle' Effects Shot

The director known simply as McG faced a major challenge: toppingthe mega-success of his original Charlie's Angels feature forColumbia Pictures. So for Charlie's Angels 2 he wanted theaction to live up to the sequel's subtitle — FullThrottle. For visual effects supervisor Mark Stetson of SonyPictures Imageworks, that meant creating a host of over-the-top shots,including a 280-frame extravaganza that sets the tone early on.

The shot finds the Angels (Cameron Diaz, Lucy Liu, and DrewBarrymore) preparing to bail out of a large truck that's careeningalong the top of a dam, high above a precipitous gorge. Diaz'scharacter has climbed into a helicopter that's beneath a tarpaulin inthe truck bed. As the vehicle hits a retaining wall at the top of thedam, the tarp is ripped off and the helicopter is thrown free. Itsomersaults into space — and the camera goes after it.“It's as if the cameraman has jumped backwards off thedam,” says Stetson.

The camera also passes through the helicopter cabin as Diazstruggles to control the craft. The other characters are tumbling fromthe doomed truck and falling toward the helicopter, desperate to getaboard. Chunks of debris and dust are raining down as well. “Bythe end of the shot everything, including the truck, is tumbling pastthe camera,” notes Stetson. “It's a lot of story to tell inone shot.”

After storyboard artists came up with an initial pass, theImageworks previz team used Alias/Wavefront's Maya running on WindowsPCs to create a choreographed version. Scans of the Angels from theoriginal film were used for the characters, while the helicopter wasmodeled with Viewpoint data. This previz was used to demonstrate theshot for everyone involved in the tricky greenscreen shoot thatfollowed.

That shoot required photographing actors on wires, as well as Diazinside a buck of the helicopter cabin (whose exterior would later becompleted in 3D-CGI.) The buck was on a programmable hydraulic base,and the camera was programmed to move through the buck via Image G'sBulldog motion control rig. Because there were so many elements to beorchestrated, Imageworks used Maya to model a virtual version of theentire setup for the crew to study. Pressed on DVDs, it showed top andside views of the stage as well as what the camera was supposed to see.“It helped us orient the motion control rig and figure out howmany sections of track we'd need for the rig, as well as exactly wherethis big hydraulic buck was going to be and where the actors wouldhang,” recalls CG supervisor Daniel Eaton.

To translate the virtual camerawork in the previz into moves thatthe actual rig could perform, they worked out a pipeline from Maya tothe Kuper motion control file format, Stetson explains. It translatedthe previz files into usable motion control material. The stage crewcould then replicate the desired camera moves — albeitconsiderably slowed down. (The frames would later be re-timed digitallyusing Realviz's ReTimer software.)

Complicating the process was the fact that the motion controlprogram had to be run in reverse. “We shot backwards,” saysStetson, “because it's much easier to pose actors in a goodposition and have them tumble out of that, rather than try to tumbleinto position.”

“There was also some concern with flying this bigmotion-control camera literally within inches of the actors hanging onwires,” Eaton adds. “By shooting in reverse, the camerastarted slow right next to them and then pulled away faster and faster,which made everyone feel more comfortable. And it allowed us to framethem a little better.” To show the actors what was expected, thepreviz was played backwards for them.

The greenscreen footage was then prepped (including wire removal)with Discreet's Inferno. The actors' tumbling performances werestabilized, and footage of Diaz in the buck had to be merged with a CGmodel of the helicopter. That CG chopper and its animated rotor blades,along with the disintegrating truck, were done in Maya on Windows PCs.The accompanying dust and debris were created with Side Effects'Houdini, running on Unix hardware.

Alias/Wavefront's StudioPaint was used to create surface textures,and the models were lit using Imageworks' inhouse lighting tool BIRPS.“There's lots of specular glints and little distortion gags onthe surfaces,” Stetson notes. “We used tricks in therepresentation of the rotor blades — a sharp version,motion-blurred versions, and sort of an occlusion pass that we ran withthe blades to take down the background behind thehelicopter.”

“Occlusion passes help figure out the densities of the shadowsin the helicopter and under the truck as well,” Eaton says.Imageworks rendered the CG with Pixar's RenderMan running onLinux-based PCs. This mix of CG and live action played out against abackground that was virtual as well.

Stetson and Eaton had photographed actual dams and canyons, andthese images were projected onto rough 3D geometry to create thebackground for the shot. The images were prepped with Adobe Photoshop,which was used to create the sky as well. “Basically, everythingis entirely texture-mapped CG,” says Eaton, “or it isre-projected matte paintings constructed from our locationphotography.” All these disparate elements were composited withImageworks Bonsai software.

Having this completely invented environment allowed them to maketotally free camera moves. “This is one of the shots where wepulled out all the stops,” notes Stetson. “Being able tointegrate motion control and CG is what this shot is really allabout.”

McG - Director

Mic Rodgers - Second Unit Director

Mark Stetson - Visual Effects Supervisor

Jonathan Taylor - Second Unit DP

Mike Swift, Adolfo Martinez - Storyboards

Matt Sweeney - Special Effects Director

For Sony Pictures Imageworks:

Daniel Eaton - CG Supervisor

Crys Forsyth-Smith - Visual Effects Producer

Jeff Lin, Pepe Valencia - Previsualization

Francisco de Jesus, Dan Ziegler - Technical Directors

Greg Derochie - Lead Compositor