Need help choosing a render engine? Part four of our guide to the subject looks at the issues involved in setting up a VFX pipeline

In issue 126 of 3D World, we look at the range of rendering software currently on the market.

In the magazine itself, you can find a guide to ten key renderers: Brazil r/s, finalRender, FPrime, HyperShot, mental ray, MachStudioPro, Maxwell Render, RenderMan, Turtle and V-Ray.

But for serious visual effects work, it’s easy to assume that there is only one renderer in town: Pixar’s RenderMan. That isn’t necessarily the case, says VFX supervisor Allan McKay, a veteran of ILM, Blur Studio and Prime Focus.

“RenderMan is great… if you have enough of a team to support it. A lot of small and mid-sized studios just automatically assume their work is going to look as good as the big boys if they use it. It’s like buying a Flame suite because you hear it’s good for compositing.”

For smaller studios, RenderMan-compliant systems like 3Delight, AIR or even the open-source Aqsis and Pixie offer many of the benefits without such heavy technical overheads, while McKay notes that mental ray is also worth considering.

“RenderMan is much more flexible and open, so it’s very fast when optimised. But mental ray is really solid for certain things like water and glass.”

MAKING AN INFORMED CHOICE
So what should determine your choice of renderer in a VFX pipeline? “The key thing I look at is speed vs quality,” says McKay. “Motion blur needs to be fast, and capable of handling atmospherics. Displacement and reflection/refractions are also killer. Same with GI.”

“Also check that the [shading language] is flexible and stable, as some have a lot of little quirks. Coming back to blank or dropped bucket rendered frames [is also vital].”

McKay notes that the new breed of raytracing renderers like V-Ray and finalRender, though popular among 3ds Max users, have taken longer to make an impact in the Maya market.

“Many [facilities] still prefer mental ray as a lighter-weight alternative to RenderMan,” he says. “Interestingly, Blur Studio switched its entire pipeline to mental ray purely because it had a nice Fast Skin shader: [for them], subsurface scattering of human skin was one of the key deciding points.”

RENDERMAN: THE GOLD STANDARD?
But among the larger VFX studios we spoke to, one renderer still dominates: Pixar’s RenderMan, also formerly known as PhotoRealistic RenderMan or PRMan.

One such studio is Industrial Light & Magic. Although ILM also uses mental ray and modo on specific jobs, Oscar-winning VFX supervisor John Knoll draws attention to RenderMan’s reputation as a production workhorse.

“RenderMan‘s widespread use among facilities whose reputation depends on creating consistently excellent imagery is telling,” he says. Its extreme flexibility, quality, robustness and scalability have made it the standard among professionals that it is today.”

MOVING AWAY FROM REYES
To a degree, market inertia also plays its part. The amount of R&D work that older studios have invested into honing a RenderMan pipeline makes many unwilling to change, unless a significantly better solution can be found.

So when Sony Pictures Imageworks announced that it was adopting Marcos Fajardo’s global illumination renderer Arnold as a major part of its pipeline, the news was greeted with interest by the 3D community.

While the Reyes rendering system used by RenderMan traditionally offers a winning compromise between speed and image quality, Imageworks believes that the complexities that Reyes methods introduce early in the production process now outweigh the speed increase during rendering itself.

Cloudy With a Chance of Meatballs image coutesy of Sony Pictures

“With our previous rendering solutions, we found ourselves managing numerous control passes,” says company CTO Rob Bredow, who also acted as VFX supervisor on Cloudy With a Chance of Meatballs, on which Arnold was used for rendering.

“For example, a complicated shot might have pre-processing passes for shadows, subsurface calculations and even indirect bounce – sometimes hundreds in total. These passes take a while to calculate and manage.”

FREED UP BY RAYTRACING?
This creates not only technical but artistic limitations, since the complexities of managing the separate passes discourage lighting artists from moving lights unnecessarily.

In contrast, a raytracing engine like Arnold offers far more scope for creative experimentation. “We find that any time before the final render has been submitted to the cue, you can move a light, change its size, or even add a blocker or bounce card… and it doesn’t ‘cost‘ any more,” says Bredow.

“It’s creatively freeing and the workflow is more akin to live-action lighting. Plus, since we aren’t using as many shortcuts, our lighting looks better and more accurate, even before the extra artistic adjustments.”

Whether more studios will follow Imageworks’ lead and move from Reyes methods to newer rendering solutions remains a matter for debate. One thing’s for certain: the market for visual effects rendering systems will be a very interesting one to watch over the coming year.