'Merlin Magic'

Category: In Focus
Arnold renderer is key

For the complex creature rendering challenges of the BBC's “Merlin,” boutique London VFX house Vine turned not to sorcery, but to Solid Angle's Arnold renderer.

Creating the visual effects for an entire series of “Merlin” would be a challenge for any company. With its otherworldly mixture of creatures, environments and wizardry – both literal and digital – the BBC's Arthurian fantasy is broadcast to millions of viewers in over 180 countries worldwide. But for Michael Illingworth, founder of boutique London facility Vine, the challenge was doubled. Before he could create the effects, he had to build a studio.

"Before we started work, there were five of us," says Illingworth, a veteran digital artist and VFX supervisor, who had handled the matte painting for the previous series of “Merlin.” “When we finished, there were 20. We had to get the whole company up and running – down to buying the desks and chairs – in three months. And of course, we had to decide what software to use."



One choice: Solid Angle's Arnold renderer.

As Illingworth can attest, Arnold is the visual effects industry's best-kept, worst-kept secret. Developed by Solid Angle founder Marcos Fajardo since 1997, this fast, physically accurate raytracing renderer has steadily built a user base that includes some of the world's major VFX studios. Sony Pictures Imageworks, with whom Solid Angle has a long-established development partnership, has used it as its primary renderer for years. Other clients include Digital Domain and Framestore. But go to the company's website, and you will be greeted only by a single, enigmatic equation: the formula for light transport through a differential solid angle of space.

"All we knew about Arnold before we got started was that big studios were using it and liked it," admits Illingworth. "But we were pleasantly surprised with the support we got from the developers and management team – and how easy it was to get beautiful images out."

Complex tasks, low render times

Rendering quality, particularly in complex 3D scenes, was a prime factor in Vine's choice of Arnold as its render engine. For the first two episodes of “Merlin” alone, the studio was asked to create two entirely new all-digital creatures: the white dragon Aithusa and the Euchdag – a 400-year-old humanoid creature who is reputed to hold the key to all earthly knowledge.



The Euchdag, a photorealistic humanoid character driven by actress Josette Simon's motion-captured performance, was to prove the show's key technical challenge.

"She's very slight, and withered and skinny," says Illingworth. "But she also has a translucent quality. Her skin refracts the light, and you can see her internal organs glowing inside. We were trying to achieve a look like a jellyfish."

To replicate the luminous, gelatinous transparency of a sea creature, Vine needed to mimic a range of complex real-world light effects, including subsurface scattering, soft shadows and multiple internal refractions. Moreover, it needed to do so in no more than 40 minutes per frame.

"It's one thing to make shots look great, but we had to prevent render times from getting out of hand," says Illingworth. "We had a colossal amount of work to do."

All told, the studio had 204 VFX shots to deliver for the first two episodes, all of which had to be completed inside six months. From starting to build assets to delivering the first completed renders took just three months. And again, Arnold played a key role.

Effects for free

"The great thing about Arnold is that you can get really nice renders right off," says Ivor Middleton, Vine's head of 3D. "It's all about the bounced lighting. It's not like old-fashioned ambient or diffuse occlusion. [Because it's a physically accurate raytrace renderer] you can put a single light into an environment and get all your indirect lighting for free.

This simplicity of workflow was a key selling point for Middleton, who also considered using RenderMan, 3Delight, mental ray, V-Ray and Houdini's Mantra renderer for the work. "With Arnold, we'd typically only have around three lights per scene: a key, fill and edge lighting. If you were lighting a similar shot in RenderMan, you would typically end up with quite a few area lights to get the set looking nice, but with Arnold, an awful lot comes from the environment itself."

And because Arnold does not need to pre-calculate secondary data like point clouds, shadow maps or irradiance caches before commencing a render, the calculation process itself is memory-efficient, placing minimal load on servers and network infrastructure, and requires little human intervention.

"If you're generating point caches, you have to go through and debug them. There's more TD’ing to do," says Middleton. "Because Arnold is handling all of that for you, it's a lot simpler."

Minimal setup times

While Arnold excels at rendering complex organic characters, they aren't its only strength. Vine's other effects for “Merlin” included digital environments, set extensions and hard-surface props: tasks the company expects to repeat on future jobs.

"Arnold worked beautifully for this particular project, but we're not going to disappear at the end of the show," says Illingworth, who is now negotiating a range of future TV and movie effects projects. "We regard our pipeline as a long-term investment."

Vine uses an eclectic range of tools for its 3D work, from 3D-Coat to Houdini, but its workhorses are Maya for asset creation and animation, and Nuke for compositing. Arnold links into this pipeline seamlessly, with Maya writing out files in its native ASS file format via Solid Angle's MtoA plug-in, and Arnold spitting out a range of render passes, both standard and user-customised, ready for compositing in Nuke. All Vine had to do was to write a few low-level Python scripts.

"We knew that we weren't going to have time to do a big setup or write shaders," says Middleton. "That Arnold worked out of the box was as important to us as what it could do as a renderer."



An ideal tool for small studios

This combination of ease of setup, raw render quality, and what Middleton describes as "very competitive" pricing, made Arnold an ideal choice for a small start-up facility like Vine. The fact that its workflow felt familiar to users of other popular render engines was a further bonus.

"Because we're a very small facility, we have to go with tools we think the artists we hire are going to pick up quickly," says Illingworth. "We thought RenderMan lighters from the movie world would be comfortable using Arnold, as well as people from TV backgrounds using mental ray."

And with Arnold now rapidly expanding from its original user base within the major Hollywood studios, Illingworth expects other small-to-medium sized studios to take advantage of its power.

"It's one of a range of fantastic tools that do tasks that would traditionally have been done by teams of in-house developers," he says. "Now small companies like us can buy them off the shelf."

Maximising artists' time

Most of all, Arnold enables CG artists to concentrate on what they do best: on creating great images, not on technical troubleshooting – something that makes both creative and financial sense, given that an artist's hourly wages are often estimated to be around a thousand times greater than one hour of CPU processing time.

"If we hadn't used Arnold, a lot more of the work on “Merlin” would have to have been done in the composite," concludes Illingworth. "We would have had to bully the render passes into working in the way we wanted. What was impressive with Arnold was that, even with just a single light, each creature sat in its environment pretty much out of the box. They looked fantastic straight away."



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