Baseblack Brings Ghostly Magic to Harry Potter

When the friends decide to return to Diagon Alley with the goblin Griphook, they travel via a four-way apparition created by CG Artist Will Correia. He developed textures for the apparating characters in Photoshop from a combination of the plate photography, reference pictures supplied by production and some original repainting, which he then reprojected onto simple gingerbread type models, rigged to deform and animate as required. All animation was completed inside Maya and rendered with mental

Having been provided with reference plates of mountains and lakes shot on location in Scotland, CG Supervisor Fred Sundqvist’s team stitched the photographic elements into a series of 24K panoramas that could be reprojected onto proxy geometry at different levels to allow visible parallax as the camera moved restlessly around. This included blending multiple plates of water together to create the illusion of a seamless lake surface moving behind them.

Compositors Peter Farkas and Sarah Juniper integrated the live-action plates into the created environment, which included water interactions as the characters emerged from the projected lake surface and blending the burnt out summertime grass of the live-action set with the lusher spring grass of the background plates. “The separate water plates were overlapped and hand-stitched with selective blending, frame by frame wherever a seam was visible in a shot. The panoramas were carefully designed to limit the amount of visible seams. The stitching and compositing were completed inside Nuke,” said VFX Producer Kate Phillips.

Lead Compositor Dave Bowman designed a look with variable displacement, animation and transparency values, which could be set separately for different sections of the cut or varied dynamically during shots to show the ghost fading in and out visibility. Kate said, “Each value was set on a different node inside Nuke and could be locked or dynamically varied within the Nuke script for each shot. The levels were set shot by shot, following the dramatic beats David Yates had specified. In one shot, to show her sudden fit of rage, several different takes of the Grey Lady’s face were combined in layers to create an unsettling, shifting look. Her teeth and eyes were scaled up and pulsating veins tracked onto her forehead and shoulders.”

Supernatural Moves
A special task for the 3D team was a look for her supernaturally rapid moves through the environment. At one point she rushes straight through Harry himself. David Yates suggested they revisit the Deluminator effect they had created in for ‘Deathly Hallows Part 1’ as a visual reference, a challenge in itself. The Deluminator was a moving point of light created as 2D animation, but the Grey Lady had to transition into that state from a full 3D human and back again within a few frames. A digital double of the character was built and developed enough to take over from the live-action performance within the one shot and then quickly shrink and elongate into a point of light.

“To signal her transition, the Grey Lady's arms and dress shredded as she picked up speed before turning into iridescent trails of light,” said Kate. “An underlying simulation of her arms, hair and dress, using MayaCloth and HairSimulation, was used as a way to create light trails inside Nuke through a procedural conversion which was hand-tweaked shot by shot. Although the double was only expected to appear for a few frames, late in production the editors needed a shot of the Grey Lady for which no footage had been captured. Fortunately she had been built at a high enough quality to appear in the shot. The artists had used their usual 3D pipeline - Photoshop for textures, modelling and rigging inside Maya - but 3D-Coat was used to re-texture her face for an extreme close-up.”

Mechanical Beauty
When Harry’s situation becomes desperate, he goes to the Forbidden Forest to sacrifice himself and finds the members of his resurrected family, again provided by Baseblack. “Unlike the Grey Lady, the characters are invoked by the Resurrection Stone, which emerges from the Snitch, which Baseblack had created in ‘Deathly Hallows Part 1’. For Part 2 we restored our existing model but it had to be re-rigged to open and also enlarged to fit the resurrection stone inside. Its elegant, mechanical animation designed, built and rendered by Robert Grbevski, composited by Joss Flores. It went through multiple design stages - we designed around six different opening mechanisms. The final version David Yates and Tim Burke selected is one of the least elaborate of the options presented. Then we then re-timed it to work within the cut editorial put together,” Kate said.

The family had to appear peaceful and serene, quite different from the Grey Lady. After trying different looks, Sequence Lead John Hardwick developed a look that softened the actors’ faces with a gentle glow. Instead of separate green screen passes, the complete sequence was shot in-camera and the characters were made transparent by rotoscoping them off the plates, repainting the background behind them and mixing them back in. This sequence included some set replacement to extend the forest further into the background, which they accomplished with layered matte paintings.

Boat House
A more complex environment replacement was required in the sequences taking place around the Hogwarts Boat House. This new set was built on a green screen stage and Baseblack added views in three directions, designed by Co-Supervisor Rudi Holzapfel. It required separate matte paintings for the sky and mountains, and a wide expanse of CG water. Kate said, “The separate matte paintings were necessary because they're all derived from photographed textures, and the skies and mountains were shot separately. All aspects of the look of the landscape were subject to extensive redesign, as well as being used to derive reflections for the water, so it was more efficient to create separate matte paintings which we could tweak individually.”

The CG water needed to blend with a pool of water on-set, close to camera, and we needed to add some fiery reflections to the surface, coming from Hogwarts which is on fire behind the characters. This wider environment was matched with some very close-up work to create a CG window through which much of the boat house is seen while Harry crouches outside. After Naweed Khan modelled and textured a window to match the on-set reference, 3D artists tracked the windows into the plates - sometimes cheating the track with animation to make sure the audience could see the action clearly - before the compositors completed the shots with various distortions to reflect the warped glass.

Ashes to Ashes
Baseblack’s work on the film culminated in a wild wand battle that erupts in the Great Hall at Hogwarts, where a duel breaks out between Molly Weasley and Bellatrix Lestrange. The fight was carried out mainly through hand-animated wand bursts, with layers of smoke and interactive lighting. Kate said, “The hero wand effects were all individually hand-painted inside Nuke. The background effects are simple roto shapes being used as grading masks. These effects were designed with a general sense in mind of the looks established on previous films, especially our own work in the Cafe Fight and Snatcher Attack in Part 1, but we weren't concerned about matching other vendors' shots since Tim Burke and David Yates liked the idea of developing individual looks for specific scenes.” Defensive shields were created by wrapping painted textures around hemispheres inside Nuke.

In the climactic shot when Bellatrix is struck down, the original plate was re-sped a fair amount to make her appear frozen in space. Because the plates were all shot at 24fps, the re-speed artefacts were corrected and re-painted by hand. A digital double then takes over and quickly deforms as her body shrinks and desiccates, and animated cracks spread over Bellatrix’s face and arms. “The cracking is produced with hand-drawn textures made in Photoshop, progressively projected onto the digital double inside Maya - essentially 2D animation being implemented in 3D,” said Kate. “At the final blow, the shrunken digital double is blown apart in an explosion created by Fred Sundqvist, designed with a combination of ncloth and nparticles inside Maya to result in burning ash falling to the ground.”