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Issue: September 1, 2004

OPENEXR: ILM'S INDUSTRY STANDARD FOR FILM EFFECTS

By: By Ken McGorry
SAN RAFAEL, CA - Last year Industrial Light & Magic (www.ilm.com) opened its proprietary image file format to visual effects practitioners and software developers.

Called OpenEXR, the ILM file format offers extended dynamic range, allowing it to act more like film - over 30 f-stops allow users to digitally "develop" their images from very dark to very light without being stuck with the few f-stops other digital file formats handle. OpenEXR is a 16-bit, floating-point file format (compared to the industry's 8- and 10-bit file formats), is fully compatible with Nvidia?s 3D graphics solutions and achieves lossless compression ratios of 2:1 for scanned film images.

The file format is available free to the industry's open source community (via www.openexr.net) and the idea is to allow more effects artists to work on films, regardless of their professional affiliation. Little guys can work more efficiently with the big guys.

"The main purpose of it is to get as much information from an image as possible," says Cliff Plumer, chief technology officer at ILM. A lot gets lost in the transfer from film to digits, Plumer says, and it's especially useful in placing a synthetic character within a live-action plate. "Principal photography schedules are getting a lot shorter, so maybe not every scene gets the necessary set-up time for lighting. This enables us to do a lot more in post production and maybe free things up a bit more during photography."

The EXR format can also benefit those shooting HD or other digital formats, although Plumer cautions that video has quite a bit less information to work with. However, EXR does mean that folks working on a no-film budget have a way to composite their effects and virtual characters more seamlessly.

"There've been 'religious wars' in the film industry about resolution, which is important," Plumer says, "but we feel that color depth is just as important - maybe more important. Whether you?re working with HD material or film material, that expanded color depth is a big win. It enables you to do a lot more than other image formats." Software vendors adopting EXR include Discreet, Alias, Softimage and RenderMan and Mental Ray support it for rendering.

And, since EXR is free, users are encouraged to give back their own innovations to the source code, too. "If you're enhancing it in any way, make that available," Plumer says.

More and more Hollywood studios are implementing EXR, Plumer says, as are most of the software vendors. "It's great for the industry, but it also helps us at ILM just being able to share the material with the other studios. Projects have gotten so large that it's difficult for any one studio to do it all so as we?re sharing assets and elements between studios, it's nice to have a common format that benefits everyone."