Digital Magic in Harry Potter and the Chamber of Secrets

Plate photography of actor Daniel Radcliffe reacting to an invisibleDobby.

A key character in the Harry Potter franchise debuts in HarryPotter and the Chamber Of Secrets, director Chris Columbus' secondfilm in the Warner Bros. series. Dobby the elf appears in Harry's roomand soon reveals forbidden information — a transgression forwhich he promptly punishes himself by hitting himself with a lamp. Asbrought to life by Industrial Light + Magic, Dobby appears to havecrawled out from under a rock, his wrinkled skin very visible beneaththe grimy pillowcase he wears.

“The big issue for this shot was the interaction between Dobbyand the environment,” explains Douglas Smythe, ILM's associatevisual effects supervisor. “Dobby jumps off a stool, leavingindentations in the seat, and knocks things off Harry's desk. And thelamp he's hitting himself with shines on everything in the room. All ofthose things had to be dealt with in one way or another.”

During plate photography, actor Daniel Radcliffe reacted to a ballon a stick that indicated where Dobby's eyeline would later be. Thecamera followed the hyperkinetic elf as well, because as Smythe says,“Lock-offs are boring and old-fashioned!”

Once the shot was scanned, Smythe's team used ILM's proprietary MARSsoftware to recover the camera move. They then built CG geometry tomatch what was in the room so they could properly position Dobby. Thescene had been photographed with props on Harry's desk, including apencil cup, photo album, and a deck of cards, but when it was decidedthat Dobby's actions would affect these props, ILM painted out theoriginals so they could be replaced with computer-animated versions.Painting was done with a combination of Pinnacle Systems' Commotion,Matador Paint, and Adobe Photoshop.

CG modeling was done with Alias|Wavefront's Power Animator, andanimation proceeded with a combination of Softimage and ILM'sproprietary Caricature software. Part of the Caricature suite of toolsis cloth simulation software, used for Dobby's clothing and theindentations he leaves on the stool's seat. “Even though Dobby'sonly about 30 pounds,” observes Smythe, “that's enough tomake an indentation, and it really helps tie him into thescene.”

ILM's Viewpaint software was employed to create the surfaces, whilethe character designers used a new proprietary tool to push and pullDobby into particular poses. “You can pull on the fingertip andthe finger will straighten. Then the hand, and the forearm and all theway to up the body if necessary — everything pulls along in aphysically believable way,” Smythe explains. “You can makeinteresting dynamic poses almost as easily as you would using thoselittle wire characters that all animators have on theirdesks.”

Wireframe model of the character.

In addition to bounding around Harry's room and whacking himselfwith a lamp, Dobby delivers rapid-fire dialogue, animated by hand.“We didn't do any mocap or facial capture at all,” Smythenotes. “We did have some reference video shot of the actor duringthe voice-over session. He had some great facial expressions and weincorporated a lot of those ideas.”

Dobby's wrinkled skin proved challenging, both in terms of how itmoved and how it was rendered. “We had a huge library of shapesthat the animators could dial in, especially around the head andvarious joints,” Smythe recalls. “But technology gets youonly part of the way. It takes an artist to finish the job, and werelied extensively on hand work for the movement of theskin.”

To light Dobby, Smythe continues, “We used a new skin shaderthat was a RenderMan implementation of subsurface scattering. This isdefinitely a step forward for skin rendering technology. With this newsystem — as with real skin — light doesn't hit the surfaceand then bounce off. It enters the surface, bounces around inside,picks up some color and then comes out. So you get a blending of thesurface color and the stuff that's underneath, combined in aninteresting way. Because skin is translucent, you see this especiallywhen light enters from behind, like through Dobby's ears. We tried toplay that up because it's a cool look.”

Dobby’s seat was created with cloth simulation software toshow the indentations he leaves.

Lighting was especially crucial to integrate Dobby into the liveaction, especially since the lamp he's brandishing creates multipleshadows. So in addition to the rendering done with Pixar's RenderMan,ILM used Mental Images' Mental Ray software to compute all of theshadows, which were raytraced with soft shadow penumbras. Because thelamplight bounces off the character onto the wall, “We made surethat the shadows weren't just darkening, but also had the rightfall-off and blurring with distance — all of the things thathappen for free in the real world,” notes Smythe.

Smythe's team did add some lighting to the plate photography sinceHarry's lamp had an open-top shade that projected a circle of lightonto the wall when Dobby turned it sideways. To achieve this, they setup a virtual rig that shadowed the bulb to create appropriate circlesof reflected light. Otherwise, relatively few interactive lightingeffects were added. “Because if you mess with your platephotography too much, it looks fake and distracting,” saysSmythe.

Final composite

Compositing all these elements was done with proprietary software,and both SGI and Linux hardware were used throughout production. WhileDobby's appearance definitely benefited from several new advances inILM software, Smythe gives the lion's share of credit to the animators'imaginations. “They were able to take what was photographed withvery little reference — just the eyeline and the camera move— and fit in a motivated performance. That takes realtalent.”

Director: Chris Columbus
DP: Roger Pratt
Visual Effects Supervisor: Jim Mitchell
For Industrial Light + Magic:
Associate Visual Effects Supervisor: Douglas Smythe
Sequence Supervisor: Indira Guerrieri
Paint and Roto Lead: Pat Jarvis
Cloth Development Lead: Juan-Luis Sanchez
Skin Shader Development: Christophe Hery
Technical Direction: Steve Molin, Bruce Powell
Character Modeling: Frank Gravatt
Viewpainter: Jean-Claude Langer
Compositor: Barbara Brennan