Harry Potter ends in a flood of VFX
The release of Harry Potter and the Deathly Hallows: Part II on July 15th 2011 marks the end of perhaps the most ambitious – and certainly the most remunerative – film cycles in cinematic history. Almost ten years on from Philosopher’s Stone, J.K. Rowling’s saga is concluded on screen, in 3D. (warning – the following contains possible spoilers)
As with Part I, the film is directed by David Yates and produced by David Heyman, David Barron and J.K. Rowling. As always, the film stars Daniel Radcliffe, Rupert Grint and Emma Watson, supported by a panoply of top British acting talent, both young and old.
For Framestore, too, Deathly Hallows: Part II marks the end of an era. The company has been a part of the cycle from the outset, contributing to every single film. Framestore’s work has included the deadly Basilisk in Chamber of Secrets, Buckbeak the Hippogriff in Prisoner of Azkaban and Dobby the House Elf’s moving final performance in Deathly Hallows Part I. The new film sees Framestore once more facing new challenges, with the company providing a brace of dazzling sequences, as well as – a bittersweet honour and pleasure, claims the facility, helping create the last sequence and shot of this last film.
After destroying one Horcrux and discovering the significance of the three Deathly Hallows, Harry, Ron and Hermione continue, in Deathly Hallows: Part II, to seek the other Horcruxes in an attempt to destroy Lord Voldemort. However, now that Voldemort has obtained the Elder Wand, he aims to complete his final stage to ultimate power and launches an attack on Hogwarts School of Witchcraft and Wizardry, where the trio return for one last stand against the dark forces that threaten to take over the Wizarding and Muggle worlds.
VFX Supervisor Andy Kind led the Framestore team’s work on the film. “Compared to our contribution to some of the other films, DH: Part II was a relatively modest affair, some 90 or so shots,” he noted. “That said, it kept us pretty busy. Not only were there challenging technical aspects to the VFX work, but the creation of our own 3D versions of these sequences to an appropriately high standard meant we had to stay on our mettle.”
The first of Framestore’s sequences takes place in the Chamber of Secrets, the underground cave system below Hogwarts, first seen in the eponymous second film of the Potter cycle. Ron and Hermione return to the Chamber, seeking one of the Horcruxes, which is in the form of a cup. Finding it, they destroy it by striking it with a tooth taken from the corpse of the Basilisk that Harry slew several years ago. As they strike, the residual malevolent energy possesses all of the water in the Chamber, causing it to rise up (with Voldemort’s face briefly forming in it) and pursue Ron and Hermione through the chamber before running out of energy and collapsing in a huge, drenching splash over them. As the waters recede, Ron and Hermione are moved to express their feelings for one another.
While HP 2 featured a fully constructed Chamber of Secrets set, the location’s quite brief reappearance in DH: Part II meant that a digital environment was the order of the day. Filmed entirely on green screen, with even the studio floor getting replaced, faithfully recreating the Chamber was actually the least of Framestore’s problems. “The really tricky thing about the sequence,” said Kind, “Was that you were dealing with this big FX water simulation, but at the same time it was a sort of character. You had to convey that it was moved by a sort of primitive intelligence and malevolence, and show these forces rising and finally exhausting themselves.”
Leading the technical charge was Senior FX TD Alex Rothwell. “We knew early on that we were going for water simulation rather than any sort of rig-based animated model, which rarely looks completely natural,” he explained. “We used Naiad, a new liquid and gas simulation tool developed by Swedish company Exotic Matter. Naiad is very good at generating natural water movement – stuff that obeys the same laws of physics that actual water does. But our water had to do so much than just look natural, which can create problems. There’s only so much control you can exert on simulated water without it looking very constrained. If you’re not careful, when you try to affect it you end up with something that looks like water being poured through an invisible glass tube. So you’ve got to keep the splashiness and fluidity, and create constraint using force rather than surface.”
In addition to an initial look/dev period, in consultation with the film’s Senior VFX Supervisor, Tim Burke, the problem of meshing had to be addressed. “Because what we produced in Naiad can’t be rendered directly through Renderman,” explained Rothwell, “The meshing stage involved a tool that Martin Preston and his R&D team wrote called fApproxDist. It takes all the points coming out of Naiad and produces a mesh which gets passed on to the lighters, and from then on it’s a lighting and shading job.”
Once the main water simulation was completed and ‘baked’, it was fed back into the system for a series of foam and spray passes, also generated through Naiad. These hang off the completed main simulation, with its various attributes driving them.
Framestore’s compositing team for Deathly Hallows: Part II was led by Christian Kaestner. “To light the Chamber we started off with pure ambient light, meaning there wasn’t supposed to be any artificial lighting in it and it was supposed to be very dark,” he explained. “But as we went through it with the client we ended up putting in lights to give the basilisk head and the chamber itself some kind of shape. We also had an extra pass – the water sparkle pass – which would give little bit of shine on the floor. This sequence was the most challenging technically, as it was something we hadn’t really pursued before.”
“We’d done the standing wave for The Voyage of the Dawn Treader (also using Naiad), but having animated water with a character to maintain, and to give it the look and feel that the client wanted, was a bit tricky,” Kaestner continued. “We found that calibrating water is just as sensitive as, say, the skin of the house elves which we’d done for DH: Part I. It has to be just right. It either tends towards tropical water – very clear – or it becomes too murky. If the viscosity and the colour aren’t just right, it starts to look like oil. There were numerous elements – subsurface scattering , how much the light comes through, how much reflection, how much detail – to be combined in the right proportions.”
The need for a 3D version added an extra wrinkle, added Kaestner. “We started off doing realistic renders of left and right eye cameras with the water, but if you calculated it correctly, we found that it didn’t work because you have different subsurface scatter and refraction and reflection in each camera which, in the real world, your eye and brain compensate for because you always converge on the things that you look at. So we ended up having to ‘cheat’ reality in order to make it look real.”
Near the film’s climax, as he finally comes to understand his own nature, Harry Potter surrenders himself to Voldemort, who casts the Killing Curse at him, sending Harry to a limbo-like state between life and death. He finds himself in a version of Kings Cross, but one very different from the station he knows. Everything has a bleached white appearance and the arches and platforms stretch off into infinity. Here he meets and converses at length with Dumbledore, his beloved – but dead – headmaster.
Their conversation concludes with Harry’s returning to earth and to battle. The initial brief for this sequence suggested a sort of ‘ice hotel’ feel, with everything somehow there but not there. Harry and Dumbledore were shot on a completely white stage.
“This allowed the comp team, lead by Russell Hoarth, to key it differently with Luma keys,” explained Kaestner, “Of course, we did have to roto bits and so on, but at least we had a better starting point than we would have had with a green screen shoot – the bounce was all white and therefore more applicable to the final look of the environment. The look development of the post-life platforms continued for many months of the post-production period. “We played around with subsurface scattering, making it look like ice, trying different levels of refraction,” Kaestner recalled. “But throughout this time we never seemed to hit just the look they were after. It was slightly stalled when, in March – very late on, really – we went back to our Art Department, led by the redoubtable Kevin Jenkins, and got them to produce some quick concept suggestions based on the renders that we had. The new look that they generated was an instant hit with the director, and from then on it got much easier, notwithstanding that it was some 40 shots and over five minutes of screen time.”
“I think it was the simplicity of look that we’d arrived at (which is actually very hard to achieve) that finally made it work,” Kaestner continued, “We took out all of the walls and arches, leaving just the roof, columns and platforms, which opened and enlarged the space, as well as making it less ‘realistic’, giving a much better sense of other-worldly infinity. We introduced 3D mist and fog as well. We played around with a very bright horizon line, which floods the whole environment with bright light. On top of that, at the request of the client, we started animating the opacity of some of the columns. It’s very subtle, but some of them phase in and out, which adds to the ‘otherness’ of the place.”
Once more, 3D presented the sequence’s compositors with a steep learning curve. “In Avatar the footage was all 3D to begin with, but here we had to work out how to bring 3D to 2D and to living people,” said Kaestner. “We ended up using rotoscope and cards in Nuke to achieve the necessary effect, which meant that you could then constrain values to the camera movement as well. So, based on the distance to camera, the characters could maintain the same volume. So that allowed us the most flexibility. Also, putting it on a card means you can actually see it in 3D space, which is a little bit easier for the artist, I think.”
Harry Potter and the Deathly Hallows: Part II closes with a simple, epilogue-like sequence that takes place 19 years after the events we’ve just witnessed. Harry and his family and friends have gathered on Kings Cross’s legendary Platform 9 ¾ to say goodbye to their children – the next generation – as they head off to Hogwarts, some for their first term.
Shot at Leavesden, with green screens and partial set, the final sequence presented no dramatic challenges to the Framestore team. A couple of animations – a chocolate frog and an origami bird – harked back to the earliest films. The platform environment was digitally extended, including some rendering and matte painting, the whole assembled as a photorealistic comp with Senior Compositor Kate Windibank as lead. The sequence was delivered to the client in 2D.
As Framestore says, it’s worth reflecting that the impact of the Harry Potter films on the UK Visual Effects industry is almost impossible to overstate. Tim Burke, who has worked as both VFX Supervisor and Senior VFX Supervisor on all of the films since HP 2, put this point across recently in The Guardian, “The UK is now recognised as the leading provider for visual effects in the world. All the studios are bringing their work to UK effects companies. Every facility is fully booked, and that wasn’t the case before Harry Potter.”