Creating 24's Mushroom Cloud

How Zoic Studios Made Jack Bauer's Day Even Worse

The new season of Fox's perennial hit 24 got off to a running start this year, as a two-night, four-part season premiere culminated in a one-two punch — first, Jack was forced to kill one of his best friends in the Counter Terrorisum Unit (CTU) in the name of national security. Then, a nuclear warhead exploded in suburban Los Angeles.

24 is well-loved for its general atmosphere of mayhem, but showing a mushroom cloud over an American city was new terrain even for that show. Could this be Jack Bauer's worst day yet? This year, 24's producers took their heavy VFX lifting to Zoic Studios, known for its work on sci-fi show Firefly and its feature-film spin-off, Serenity. We asked CG supervisor Jarrod Davis to fill us in on their work so far.

FILM & VIDEO: Talk about the mushroom cloud effect from the 24 series premiere. How was it visualized, and then how was it actually executed?
JARROD DAVIS: The mushroom cloud is one of the most recognizable, iconic images in the modern world. It occupies a space in everyone's head, and there's an instant emotional reaction to it. So, we wanted to keep it a very traditional shape. There's no shortage of reference footage of something very close to what we wanted, so working with 24 production — who are great to work with, by the way — we chose the piece and set about making it happen.

The actual execution of the elements was a combination of Lightwave 3D's hypervoxels, a volumetric plugin for Lightwave called Dynamite, and Re:Flex Warp in [Discreet] Combustion. I used hypervoxels for the "stem" of the cloud, because I've been using them for years and I knew I could quickly get just what I wanted. Initially, I toyed with doing an actual fluid simulation in Maya to drive Lightwave particles, but it ended up being too complicated and uncontrollable. The problem with using fluid sims is that they actually behave like reality, and we all know how cooperative reality is.

The more I studied just the stem of the clouds in the real footage, the more I saw how very simple the motion of the stem was. Despite the complicated thermal dynamics, visually it just looks like a vacuum cleaner in the center of the mushroom "cap" sucking dirt up into the stem. And the closer you get to the center of the cap, the faster it moves. So I ended up making a cloud of random points, shaping them a little bit with a magnet tool, and then just doing a simple morph on their position. Attach hypervoxels, render, done.

The cap of the cloud took the longest to put together. The rolling effect of the mushroom cap is arguably the most recognizable part of the nuclear cloud experience. Everyone alive today has been inundated with these images. We know what they look like, so I knew I had to get it just right.

Of course, while I could easily have spent a couple of months developing this look, we did have a delivery date. Early on, I chose to use Dynamite in Lightwave for the rendering of the cloud because it has an incredible internal-light shading model, with simple, efficient controls. Dynamite allows you to set a "fire temperature" and an outside cooling percentage. Dialing those two values allows you to set exactly how hot the center gets and how that falls off to the outside of the cloud. They're also animatable, so as the cloud gets older, I can make the internal fire die down, in a realistic manner. Unlike hypervoxels, which attach to points, Dynamite allows you to attach voxels to polygons, which gives you the ability to rotate them. I ended up with a semicircular array of about 25 polygons, with their rotations all tied to one so that they all had a consistent speed. Then I offset each one's size a bit to give some unevenness to the cloud. When rendered, the clouds all blend together to make a seamless whole. For compositing purposes, I rendered the "front half" of the cloud and the "back half" separately.

In the composite, the first step was to do a 2D track on the panning and zooming plate to get it moving correctly. Then I pulled out Re:Flex Warp and started going to town. There was a lot of 2D and time warping on the elements to get them to go exactly where the client wanted them to, and to give them some variety. They were long renders — the front side of the cap took four hours a frame — so I didn't want to get into a cycle of re-rendering. I put just a bit of variation into the cap in 3D and did the rest with Flex Warp, drawing splines around the rendered element to define the borders and then another spline to reshape them. I did the same with the stem, thinning it out a bit, stretching it vertically, and making sure that the end sat correctly in the middle of the cap. I layered the front cap render on top, the stem below that, and the back half render below. Then I masked a shadow line across the stem to look like the cap was casting shadows. I added some glow using Combustion's built in glow, which is very good, and also just screening Gaussian-blurred, high-contrast versions of the front cap element on top. Film grain, which is quite heavy as part of the style on 24, went on last, and voila: nuclear explosion in Valencia. Which, ironically, is where I live.

Describe some of the more invisible FX work you're doing on the show.
I like to think that the subway explosion sequence was mostly invisible. I was quite pleased with the way that turned out. It was a real team effort between myself and compositors Eric McAvoy and Spence Fuller. Then there are the even more subtle things. For example, when Jack is forced to shoot Curtis, the way the scene played out in the edit, production felt it wasn't quite clear who had shot him, so they asked us to add a bit of smoke coming out of his gun barrel, so there's no question. So there's an example of using VFX to tell the story. In a later episode, we added blood to the shirt of a victim of.very bloody treatment. In another episode, we enhanced practical explosions by adding even more explosion and debris. Even though the practical explosions went off properly, in the end, production wanted more, and with us, the digital Swiss army knife in their back pocket, if things don't quite work out practically, they have the ability to choreograph and compose things the way they really envision them.

What's new in your FX pipeline? And what's been key to your ability to jump from spots to episodics to features?
The focus for our pipeline lately has been standardization and automation. We've got a unified structure now that's standard between all types of FX work, be it commercial, game, film, episodic, or even web, but it's also flexible enough to adapt to special cases when necessary. And there's a lot of input from the artists, which is crucial, because designing a pipeline can very easily turn into something that artists have to work to use, rather than something that works for them. After standardization comes automation, automating as many repetitive tasks as possible, so the artists and producers can spend more time on work and less time on managing their workload.

I think the key to the ability to jump from spots to episodics to features has been our people. We have a ton of people who are really versatile. Some are 3D artists who also composite, or compositors who also do 3D. Some are compositors who are very flexible in what they do, from very stylized work like CSI to the "invisible" FX like in 24.

We have very, very few specialized people, and absolutely no prima donnas. We also have a crew of producers and creative management that have a lot of experience in a wide variety of commercial, film, and episodic work. There aren't many types of visual effects out there that someone here hasn't worked on before. And when we do encounter those, everyone's excited to jump in and be a part of figuring it out.