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Making it BIG: Episode II – The IMAX Experience

In less than a month, select IMAX ® theaters across North America will play Star Wars: Episode II Attack of the Clones in its largest format ever. This is not just a re-projection of the standard-sized 35-mm film print onto a larger screen; through the revolutionary IMAX DMR ™ process, the movie has been re-mastered and the image enlarged to occupy up to eight stories of screen and the sound enhanced to include 12,000 watts of uncompressed sound.

Imagine the blue-white shafts of laser energy spearing the immense Trade Federation core ship, and suddenly you’re engulfed in a cloud of dust as the fallen vessel strikes the Geonosian surface. Picture twisting and diving through the luminescent skylanes of Coruscant, as panicked commuters soar directly at you. Or imagine a forty-foot tall Yoda, using the Force to draw his lightsaber as he gets ready to square off against Count Dooku.

“The biggest thing when you get get that kind of sound and that size of image on the screen, is that it draws you into it. You’re part of the experience,” says Brian Bonnick, the Vice President of Technology for IMAX Corporation.

Up until the innovation of IMAX DMR technology, there was no way to project a standard-sized live action film to the scale of an IMAX movie and still maintain a quality performance. IMAX theaters were built for 70mm film format; smaller film formats are comprised of a fine grain structure that would be magnified and detract from the underlying picture, creating a soft, unfocused and poor image. IMAX DMR digitally removes the grain and preserves the quality of the image, allowing it to be projected onto IMAX screens.

The majority of Star Wars fans saw Episode II in a 35mm film format. This means that each film frame is 35 millimeters across. The film area is mostly square — a special lens on the projector spreads the image out to its rectangular proportions. If you were to look at a film frame from a reel of Episode II, the characters would look very tall and skinny (the Kaminoans even more so). The image is compressed into the frame and the projector lens decompresses it. On each side of the image, there are four sprocket holes or “perfs” (short for perforations), which the projector uses to tug long lengths of film through its inner mechanisms.

IMAX is a totally different picture. It’s 70 millimeters wide, and the image isn’t compressed. It’s about 10 times larger in area than 35mm film stock. It’s called 15/70mm format for the 15 perforations that run along the top and bottom of the frame. Regular movies spool into a projector vertically; IMAX projectors move film horizontally for reasons explained later on.

To get a movie projected to the IMAX scale requires a lot of image area within the film frame, and a lot of light shining through it. A 35mm film frame just doesn’t have the resolution to hold up to that scale, and a typical 35 mm projector just can’t crank out the kind of light an IMAX’s 15,000-watt xenon bulb can.

So IMAX DMR technology figured out a way to scan a 35mm film frame, enhance it, and enlarge it to 70mm without sacrificing image quality. “IMAX has been working on this innovative technology for the past five years to enhance the theatrical experience, offering movie-goers an all-encompassing experience which literally brings them into the story ,” says Bonnick.

The first feature film to undergo this process is the recently released Apollo 13: The IMAX Experience. The Ron Howard-directed film was shot in Super 35mm. That film was scanned and converted into a digital form at the highest possible resolution.

“We then apply our proprietary software and it mathematically analyzes and extracts the important image elements from each frame from the original grainy structure,” explains Bonnick. “It creates the most pristine form from the original photograph. It’s clearly the most complex step in the whole DMR process.”

The complex software algorithms makes images sharper and improves the contrast on a frame-by-frame basis. Colors are adjusted to the unique technical characteristics of the IMAX screen. If there are any scratches, blotches, or imperfections in the film image — known as artifacts — those are digitally removed by a special patent-pending process. “We clean the whole thing up from front to back end,” says Bonnick.

Once the entire film has been digitized and enhanced, it is then output back to film, but this time in 15/70mm stock. “This conversion from digital back to 15/70mm is accomplished by using our proprietary 15/70 laser film recorder. It was both designed and manufactured by IMAX. It is capable of providing greater dynamic color range than normal scanners on the market and it has capabilities of capturing resolutions up to 8,000 x 6,000.”

For Apollo 13, once the film was digitized, it comprised nearly 200,000 frames of data. “When we were finished the conversion process, we had over seven terabytes of data — that’s 12 zeroes. That’s equivalent to about 13,000 DVDs of data. Episode II is comparable in frame count. There’s a massive amount of information we’re working with,” says Bonnick.

“People tend to get mixed up thinking that DMR is just a piece of software,” he continues. “IMAX DMR is a total process that clearly involves some very complex software algorithms that process image data, but along with that comes the management of that information. You have to have an infrastructure capable of knowing where every frame is in the process to manage this much.”

Digital to IMAX

With Episode II, the DMR process was spared a step in that the image content already existed in a digital state; there would be no film to scan. But starting from an HD-source brought its own technical issues, as the algorithms set in place for handling a 35mm source wouldn’t entirely suffice for the re-mastering of Clones.

“In a digital film, it doesn’t obviously have grain that we’ve come to know in normal photography,” explains Bonnick. “But it does tend to carry ‘video noise’ artifacts. Two noticeable ones would be when pixels appear to be off-color relative to those in the surrounding area. You might get a flicker from frame to frame. Or when tighter clusters of pixels tend to slightly vary in color from frame to frame. That tends to happen in dark areas, and it looks a bit like a boiling effect. Now these are very, very subtle effects; in most cases I’d have to take you into a theater and describe to you what to look for and you would find it. Somebody who is very up on video would really pick these sort of things up; obviously, in our industry that’s part of our job.”

The DMR pipeline was customized to deal with these unique forms of artifacts. “We’ve designed it to be very open-ended. If we come across an artifact that we’ve never dealt with before, we’re in a position to very quickly write a new algorithm and incorporate it into the production engine in a short period of time.”

Though the software examined each and every frame of image, the re-mastering team broke the film down into shots as discreet units of work and focus. An individual shot (a sustained hold from a camera vantage point prior to it cutting to the next “shot”) is fairly uniform in its re-mastering requirements, though if there are specific artifact issues within a shot, the team then redirects their efforts to the more focused scale: individual frames.

The image re-mastering process took about 14 weeks of work, and was finished by the end of September 2002. “The process is scalable,” says Bonnick. “At the moment, we’ve got dozens and dozens of computers in our render farm. It’s all a factor of how many frames per day you want to process. If you want to process more frames per day in a given timeline under a tighter deadline, then you would scale up the numbers of computers in your system to give you greater throughput capacity.”

The IMAX Experience™ is more than just big picture. It also delivers six-channel uncompressed multi-speaker sound that further completes the audience’s total immersion into Episode II. “We use six completely discreet channels plus subwoofers on their own separate channels. We use ultra-low distortion amplifiers, capable of delivering up to 12,000 watts of power. We employ our own custom-designed speaker-set with over 44 speakers,” explains Bonnick. That sound system is carefully aligned by lasers to deliver proportional point source (PPS) quality.

“The non-technical definition of a PPS speaker is that we have designed it such that, rather than having the dead-center seat in the theater being the ‘sweet spot,’ these speakers are designed to enlarge the sweet spot quite a bit so that everybody in the theater is sitting in a good position to hear the sound as it was originally intended,” explains Bonnick.

The IMAX sound system will not only deliver huge events like the shattering of asteroids or the crash of a core ship, but also soft sounds like the distant birds of Naboo or the hum of background cloning machinery with crystal clarity. “The IMAX sound system has been designed with a very high dynamic range, unlike 35mm theaters. There, when you start to get anything with depth or volume to it, you tend to hear a lot of distortion.”

Those fortunate enough to have caught the original digital exhibition of Episode II in the spring are probably digital-converts, fully aware of the limitations of traditional film. IMAX film is a whole different set of variables, since the quality-assurance and technical advancements in projecting films of this size help overcome many of the limitations of 35mm exhibition.

“IMAX film lasts substantially longer than 35 mm film, because we use the rolling loop technology in our projectors,” explains Bonnick “The film is moved around the lens aperture in a wave motion. We’re not moving it constantly through sprockets that over time wear the film out and enlarge the perforations, which is when you start getting a jiggle in the film. Because of this fluid motion that the IMAX film goes through, we are being very gentle to it, ergo it lasts longer.”

An IMAX projector has a steadiness of .004 percentage change from frame-to-frame. A traditional 35mm film has a .12 steadiness in comparison. Even the heat of the projection bulb will cause a 35mm film to buckle, something that can’t happen in an IMAX projector thanks to a field flattener that holds the film steady and true.

Furthermore, the smaller number of IMAX screens makes quality assurance easier to manage. “The systems are constantly being tuned to ensure the films are running properly, that the steadiness is accurate, and the light intensity and distribution of it are all set adequately, that the screens are clean, that everything is at optimum performance levels.”

An IMAX projector is an immense machine, weighing in at over two tons. The huge platter that spins the oversized film has an upper limit of film length. Most films that play in IMAX theaters are documentaries that don’t clock in much over an hour in length. Feature films have to be cut to 120 minutes since that is the current maximum the platter can sustain. For number-minded trivia fans, the Episode II IMAX print is 58 inches in diameter and weighs 390 pounds! “It’s the limit now,” explains Bonnick. “We are actively developing a 150-minute solution that would be employed as an upgrade to the theaters in the future.”