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Rhythm & Hues Lets the Cat Out for Hat Visual Effects

Rhythm & Hues used Side Effects Softwares Houdini to create the surreal visuals for THE CAT IN THE HAT. 3D animation and effects included clouds, vapor, flying goo, a churning Vortex, motion-blur "streaks" for Thing 1 and Thing 2, authentic water interaction between a fish and its bowl, incidental effects for a multi-armed clean-up car and numerous supporting effects.

"This was the first production experience for many of our artists and that added a certain challenge, said FX lead Caleb Howard, Rhythm & Hues. To keep new artists productive under a demanding schedule, we needed to keep the amount of new information they had to retain to a minimum, which demanded having a robust but encapsulated toolset in place. In the case of this show, we were able to develop tools for each effect and train the artists in the use of those tools only. The ability to create an effective toolset that can be used without prior knowledge of the broader array of the Houdini feature set means artists can become efficient with a powerful application very quickly in a production context."

Rhythm & Hues built workflows around Houdini allowing different effects tools to be evolved and maintained in multiple versions, which could be given to the artists who required them without affecting the tools being used by others. A large portion of shots revolved around volumetric effects created via the facility's "Cloud Tank" tools, an integrated in-house system shaped around custom Houdini surface and shader operators.

The most challenging effects were for the Vortex, a tornado-like dimension. To render the material and seamlessly incorporate digital and photographic 3D objects, an adaptive ray marcher was put together using VOPs, Houdini's streamlined graphical interface for the VEX scripting language. In addition, Rhythm & Hues used Houdini's new volumetric texturing tools.

Globs of goo that fly around indoors and interact with the live-action set were also created in Houdini. The film required motion-blur streak effects for the movement of characters Thing 1 and Thing 2. The "Thing Trails" needed to work in two different pipelines, one for the live-action actors and another for digital actors. Rhythm & Hues had an additional pipeline dedicated to water interaction effects for the film's fish and fish bowl sequences. These effects were done using an in-house water simulation software with a front-end Houdini interface linked up via the Houdini Developers Kit (HDK). Artists handed off animated geometry to tds, who then ran realistic simulations of water as it would react to the fish, the glass and other elements.

"CAT IN THE HAT was complex from an organizational point of view," said Rhythm & Hues visual effects supervisor Doug Smith. "Usually, you have a high volume of shots that are similar and fit into one main category; on this film, we had people working on four effects pipelines with lots of overlapping in between. They always say you can do anything you want in production with enough time and money. The reality, of course, for visual effects producers is that you need to do things that are new and different, yet are still achievable in a practical sense."

Rhythm & Hues' film division is a preeminent producer of visual effects and character animation, with a track record of more than 75 feature films. In 1995, the studio was recognized with an Academy Award for Best Visual Effects for its work on BABE. For more information, visit

Established in 1987, Side Effects Software is a world leader in the development of advanced 3D and 2D graphics and special effects software for use in film, broadcast and game development. It is a leader in the field of non-linear animation with its unique, award-winning Houdini technology. For more information, visit

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Rick DeMott
Animation World Network
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