I.E. Effects Gets Immersed in the World of Harry Potter

Labour Intensive
Converting a 2D film to stereo 3D with results that look natural is labour intensive. To create the two separate images required for stereo content from a single frame, adjustments are made to the viewing angle for each element in the image. The process starts with rotoscoping elements out of the image and assigning depth values to them to make different parts of the picture seem closer or farther away. The depth values allow the artists to reposition each element for the right and the left eyes. Once in place, the missing details for the left and right eye images need to be painted in frame by frame.

“We received a fairly comprehensive data package from Warner Bros. for our conversion work,” David said. “It included everything we might need. The most helpful for the film’s opening Shell Cottage sequences were the dimensions of the set, and lens information. Using this information to build an accurate 3D model of select areas of the cottage and 3D tracking the frame sequences allowed us to lay in most of the main structure very accurately. Using the depth cues generated by this process allowed us to place additional talent, furniture and props correctly in 3D space.”

Also, the stereographer and director may decide on a more subtle feel during indoor dialogue sequences, because heavy-handed use of 3D can sometimes detract from an intimate exchange.
“Finding the proper depth ‘feel’ within a scene can be a great challenge, but its importance cannot be overstated. Odd and unnatural depth can quickly separate the viewer from an intended experience,” said David.

Several shots in the opening sequence included very fine elements, such as hair blowing in the wind. “The Ollivander character is a wise old wizard with wispy hair,” said Michel. "Hair is an interesting challenge for any kind of visual effects work. For this film we had a small team of artists painting and tweaking individual strands for some time until we got the stereo 3D just right.”

Defocused areas of the frame create a different kind of challenge during conversion. If a filmmaker uses a narrow depth of field to draw the viewer's attention to an area in the image, the soft-focus or blurred foreground and background elements have to be handled carefully. The soft-focus parts of the shots need some creative feathering of the depth matte. An artist can manipulate this falloff in order to minimize pulling forward background imagery inappropriately. “Stereo conversion is as much an art as it is a science, so we look at every shot individually and approach it in a handcrafted way,” said Michel. "It is not something for which you can just push a button and let a machine do the work."

Shape, Distance, Composition
David explained some other considerations. “3D across single elements would generally depend on the angle at which the object in question is represented, and its distance from the camera. If a large building were shown face on, it would require very little depth change across its surface. But if we were looking at the corner of the same building you would more than likely want to build ramps into your depth matte to represent the sides of the building falling of into the distance.

“The shape of an object, as well would dictate the type of depth treatment. A cup, for instance, would fall off into further distance at its sides. This should be represented in the depth build, provided the object is adequately represented in the foreground. Objects that fall within the background of a scene will naturally start falling flat the further their distance from the camera. Sculpting depth across background objects becomes less necessary, and can actually harm the stereo composition if used inappropriately.”

Depth Wedges
I.E. Effects worked with the onset stereographer almost daily. He would relay the director's notes and feelings regarding a particular shot or sequence, and the team would implement these comments as quickly and accurately as possible. “We also built several depth wedges in order to show an array of different treatments, allowing the director to play with the 3D space and ‘feel’ out the most appropriate depth for the sequence in question,” said David.

For rotoscoping and reassembling the images, the artists use Nuke combined with their own in-house software to drive the workflow and link the company's two locations. “We use automation to expedite the steps in the process, but this kind of work always comes down to the artist’s eye and a lot of patience.

“The values for the depth mattes that we generate are assigned within Nuke using a proprietary I.E. toolset, and we have several other tools in our pipeline to aid the conversion,” David explained. “We utilize 3D packages such as Maya, modo and Lightwave, plus 3D tracking software and other compositing packages that may have specific strengths. But whenever an off-the-shelf tool falls short of our needs, we will try to build a tool to get the results we’re looking for more efficiently.”

Dialling Depth
Some of the vfx vendors on ‘Harry Potter’ were responsible for delivering some of their own shots and sequences in stereo. “Being aware of how other vendors’ teams approached the process was helpful, but as you might imagine, many have their own proprietary process, as we do. So for this reason, the information isn’t always made readily available, as helpful as it may be.”

The I. E. Effects team worked on several sequences, in particular from the film’s opening scenes at Shell Cottage. David described some of the more interesting shots. “Getting the depth dialled in for the dialogue between Olivander and Harry was challenging and, creatively, also a great deal of fun. For example, manipulating the 3D space in one of the last shots in this sequence allowed us to profoundly enhance the narrative.

“As the camera pulls away from Olivander sitting in his chair while Harry and his group are leaving the room, the director required that Olivander feel very alone in the space. To achieve this, we had to exaggerate certain areas of the basic depth, slightly miniaturizing Olivander in effect while making the room feel larger then it was. This made the character feel rather alone and helpless.

“Challenges from other sequences involved a very soft focus and rack during an extreme close-up of Hermione, as well as an exterior scene in which Harry examines a shard of mirror.”

Here to Stay
David feels certain that although some people may think it's a gimmick, stereo 3D is here to stay. "We've seen a lot of sensational 3D in recent years, where objects erupt out of the screen into the audience, but gags like that get old fast. That is not what 3D is about."

Instead of coming out of the screen, he feels that good stereoscopy is more subtle and pulls the audience in, making it feel comfortable and natural. “3D is about providing an immersive experience that is as close to real life as you can get in the theatre. It's like 'visual surround sound,' making the story that much more immediate. Just like when movies were given sound, and then colour and then special effects, 3D is a powerful addition to the filmmaker's toolkit when it's used properly.” www.ieeffects.com