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How Digital Cinema Works


The typical American household is loaded with digital technology. A well-equipped house might have:

Clearly, digital technology has already taken over much of the home entertainment market. It seems strange, then, that the vast majority of theatrical motion pictures are shot and distributed on celluloid film, just like they were more than a century ago. Of course, the technology has improved over the years, but it's still based on the same basic principles. The reason is simple: Up until recently, nothing could come close to the image quality of projected film.

But things are starting to change. George Lucas kicked off the digital cinema charge in May of 2002 with "Star Wars: Episode II, the Attack of the Clones," the first big budget live action movie shot entirely on digital video. Most theaters played 35-mm film transfers of the movie, but some played it on digital movie projectors. Film never entered the picture. With more and more filmmakers embracing the new technology, including big names like Steven Soderbergh and Robert Rodriguez, digital cinema is well on its way.

In this ­article, we'll find out what digital cinema is all about, and we'll see what it means to the film industry. As it turns out, the rise of digital cinema will have a pretty big effect on the world. ­

Elements of Digital Cinema

Digital cinema is simply a new approach to making and showing movies. The basic idea is to use bits and bytes (strings of 1s and 0s) to record, transmit and replay images, rather than using chemicals on film.

The main advantage of digital technology (such as a CD) is that it can store, transmit and retrieve a huge amount of information exactly as it was originally recorded. Analog technology (such as an audio tape) loses information in transmission, and generally degrades with each viewing. (For more information, see How Analog and Digital Recording Works.)

Digital information is also a lot more flexible than analog information. A computer can manipulate bytes of data very easily, but it can't do much with a streaming analog signal. It's a completely different language.

Digital cinema affects three major areas of movie-making:

  • Production - how the movie is actually made
  • Distribution - how the movie gets from the production company to movie theaters
  • Projection - how the theater presents the movie

In the next sections, we'll look at each of these areas in detail to find out how digital cinema is different from conventional cinema.

Production

With an $800 consumer digital camcorder, a stack of tapes, a computer and some video-editing software, you could make a digital movie. But there are a couple of problems with this approach. First, your image resolution won't be that great on a big movie screen. Second, your movie will look like news footage, not a normal theatrical film. Conventional video has a completely different look from film, and just about anybody can tell the difference in a second.

Film and video differ a lot in image clarity, depth of focus and color range, but the biggest contrast is frame rate. Film cameras normally shoot at 24 frames per second, while most U.S. television video cameras shoot at 30 frames per second (29.97 per second, to be exact). Most video footage is also interlaced -- each frame is split into two sets of horizontal lines that fit together. Video is designed this way to work with the standard television format. A television's electron beam paints every other line as it moves down the screen (for example, every odd-numbered line). Then, the next time it moves down the screen, it paints the even-numbered lines, alternating back and forth between even-numbered and odd-numbered lines on each pass. (See How Video Formatting Works for more information.)

All of these factors give conventional video a completely different flavor than film -- the image seems to move differently. In order to mimic the characteristic look of film, movie-makers use digital camcorders that shoot like film cameras. For example, George Lucas shot "Attack of the Clones" with Sony HDW-F900 HDCAM camcorders outfitted with high-end Panavision lenses. These camcorders can shoot conventional 30-frame interlaced footage, but you can also set them to shoot 24 frames per second, just like film cameras. On this setting, the camera can shoot progressive video -- video made up of complete frames instead of interlaced fields. The camera also has a similar light range and depth of field to film cameras.

These professional digital camcorders work on the same basic idea as cheaper consumer models. They use charge-coupled devices (CCDs) to convert the incoming light from a scene into an electronic signal, and an analog-to-digital converter to turn this signal into a stream of 1s and 0s. (See How Camcorders Work for details.)

Other than frame rate, the main difference between a professional camcorder and a consumer model is image quality. Professional camcorders use higher-resolution CCDs to pick up more information from the scene. For example, the HDW-F900 records 1920 x 1080 pixels. They also use more CCDs than cheaper models. Inside the camera, a beam splitter separates the light from the scene into red, green and blue light. The camera records each color of light with a separate CCD in order to capture the full color range. When you recombine these colors, you retrieve the full color image. Cheaper camcorders use a single CCD to capture all colors of light, which compromises image quality a good deal.

Sony HDW-F900 camcorders record in a high-definition format called HDCAM, which is designed to rival film in image resolution and to adapt well to a variety of other video formats used around the world. Check out Sony: HDCAM for more information.

Experts disagree on whether digital video is up to the quality standards of film, but it is definitely close. If a filmmaker is satisfied with the image quality, there are some distinct advantages to using video, as we'll see in the next section.

Production Benefits

Apart from image quality, there are two huge differences between film and digital video: cost and flexibility.

Cost

Film is hundreds of times more expensive than digital video. The raw video alone is extremely cheap, and there is virtually no processing involved before the editing stage. Filmmakers on a real shoe-string budget can even re-use the tape multiple times. By Hollywood standards, digital video costs nearly nothing.

The "Star Wars" crew can definitely back this up. In an interview with Cinematographer.com, Rick McCallum, one of the producers on "Attack of the Clones," said they spent $16,000 on 220 hours of digital tape, and they would have spent about $1.8 million on 220 hours of film.

Flexibility

For the filmmaker, the most exciting element of digital technology is how easy it is to use. Most filmmakers have already switched to digital editing systems because they make it so much simpler to put a movie together. In the current process, filmmakers actually convert the film footage to a digital format for post-production and then back to film again for its theatrical release. The conversion process is costly, it ends up degrading the image quality somewhat, and it takes time.

Digital video doesn't have to go through this conversion process. As soon as they shoot digital footage, filmmakers can immediately play it back and start editing it. With film, they have to send the footage off for processing before they know what they have. A director might spend all day shooting only to discover the lighting was off and the footage is totally unusable. On the "Attack of the Clones" set, the crew could review the footage after every shot. They could shoot a scene in the morning and start editing it that afternoon.

Additionally, the crew doesn't have to get extensive coverage (repeated takes) in case something looks wrong. They know right away if there were any problems.

Distribution

For the business side of the movie industry, the most compelling aspect of digital cinema is distribution. In today's system, production companies spend a lot of money producing film prints of their movies. Then, working with distribution companies, they spend even more money shipping the heavy reels of film to theaters all over the world, only to collect them again when the movie finishes its run.

Because the distribution costs are so high, production companies have to be extremely cautious about where they play their movies. Unless they have a sure-fire hit, they take a pretty big risk sending a film to a lot of theaters. If it bombs, they might not make their money back. (See How Movie Distribution Works for details.)

If you take the physical film out of the equation, things get a lot cheaper. Digital movies are basically big computer files, and just like computer files, you can write them to a DVD-ROM, send them through broadband cable or transmit them via satellite. There are virtually no shipping costs, and it doesn't cost the production company much more to show the movie in 100 theaters than in one theater. With this distribution system, production companies could easily open movies in theaters all over the world on the same day.

The digital distribution system also helps out the individual theaters. If a movie sells out, a theater could decide to show it on additional screens on the spur of the moment. They simply connect to the digital signal. Theaters could also show live sporting events and other digital programming.

Projection

Photo courtesy Texas Instruments

To the audience, the most important aspect of digital cinema is the projection system. This is the final piece of technology that controls how the movie actually looks at the end of the line.

Pretty much everybody agrees that a good film projector loaded with a pristine film print produces a fantastic, vibrant picture. The problem is, every time you play the movie, the film quality drops a little. When you go to a movie that's been playing for a few weeks, you'll probably see hundreds of scratches and bits of dirt.

Many critics hold that a projected digital movie is inferior to a pristine film print, but they recognize that while a film print gradually degrades, a digital movie looks the same every time you show it. Think of a CD as compared to an audio tape. Every time you play an audio tape, the sound gets a little warped. A CD's digital information sounds exactly the same every time you listen to it (unless it gets scratched).

Today, there are two major digital cinema projector technologies: Micromirror projectors and LCD projectors.

Micromirror projectors, like Texas Instruments' Digital Light Processing (DLP) line, form images with an array of microscopic mirrors. In this system, a high-power lamp shines light through a prism. The prism splits the light into the component colors red, green and blue. Each color beam hits a different Digital Micromirror Device (DMD) -- a semiconductor chip that is covered in more than a million hinged mirrors.

Based on the information encoded in the video signal, the DMD turns over the tiny mirrors to reflect the colored light. Collectively, the tiny dots of reflected light form a monochromatic image. To see how this works, imagine a crowd of people on the ground at night, each holding a square-foot mirror. A helicopter flies overhead and shines a light down on the crowd. Depending on which people held their mirrors up, you would see a different reflected image. If everybody worked together, they could spell out words or form images. If you had more than a million people, pressed shoulder to shoulder, you could make highly detailed pictures.

In actuality, most of the individual mirrors are flipped from "on" (reflecting light) to "off" (not reflecting light) and back again thousands of times per second. A mirror that is flipped on a greater proportion of the time will reflect more light and so will form a brighter pixel than a mirror that is not flipped on for as long. This is how the DMD creates a gradation between light and dark. The mirrors that are flipping rapidly from on to off create varying shades of gray (or varying shades of red, green and blue, in this case).

Each micromirror chip reflects the monochromatic image back to the prism, which recombines the colors. The red, green and blue rejoin to form a full color image, which is projected on the screen.

LCD projectors, such as JVC's Digital Image Light Amplifier (D-ILA) line, work on a slightly different system. These projectors reflect high-intensity light off of a stationary mirror covered with a liquid crystal display (LCD). Based on the digital signal, the projector directs some of the liquid crystals to let reflected light through and others to block it. In this way, the LCD modifies the high-intensity light beam to create an image.

There is a flip-side to digital projector technology. In both projector designs, individual pixels may break from time to time. When this happens, it degrades the image quality of every single movie shown on that projector. In contrast, if a film print gets scratched, it's only that particular movie that's damaged -- the next print looks fine.

Making it Happen

It's a given that at some point, digital cinema will replace the old film system. The question is when and how.

George Lucas and many other filmmakers say it's already time to make the switch to digital production, as its quality is comparable to film and it's much easier and cheaper. Others aren't ready to give up the old standby so quickly, noting that despite what Lucas says, digital video hasn't yet reached the level of film. As technology improves, however, digital video will likely find more converts. Eventually, digital production's main obstacle will be nostalgia and familiarity. Film has served Hollywood well for decades, and it will be hard to give it up.

Digital cinema makes a lot of economical sense on the distribution front, but it would involve huge changes in the industry. For one thing, distribution companies wouldn't have nearly as much work to do -- it's a good bet it would cut down their workforce considerably. Even if the result is a cheaper distribution system, the restructuring could be a major hurdle.

The other obstacle is piracy. To make off with an illegal copy of a movie on conventional film, a bootlegger either has to hold up a delivery truck or sneak a camcorder into a theater. In the first case, bootleggers have to use expensive machinery to make video copies, and in the second, the pirated tapes really don't look that great.

But if a movie were already in the form of bytes of data, anybody could make an exact copy by hooking into the data stream. To make broadband and satellite transmission feasible, the movie industry will have to come up with advanced encryption schemes.

To movie theaters, the main obstacle to digital cinema is money. Today, it costs somewhere around $150,000 to convert a film theater auditorium into a digital theater auditorium. Most movie theaters aren't going to do this unless they're compensated in some way. After all, the production and distribution companies will save millions and millions if the switch to digital is successful, but the theaters will be conducting business as usual.

In the end, the most important question about digital cinema is how it looks to the audience. Digital cinema's proponents cite market research showing that audiences generally prefer the look of digital movies to filmed movies, but many movie buffs aren't so sure. Digital cinema will have to win over a large majority of movie fans before it can completely take the place of film.

Another concern is the convergence of home entertainment technology and professional theater technology. Today, there is a huge gap in image quality between high-end digital projectors and home models, but they are actually built on similar technologies. As home theater projectors improve and drop in price, will people still bother to go to the movie theater? In the past, the difference between film and conventional TV was huge, and theaters still had a hard time packing in crowds. In order to keep the business alive, theaters may have to add a lot more than new projectors.

Fortunately, transmitting video digitally also opens up possibilities for improved surround sound, varied programming and interactive cinema. If production companies and theaters fully explore the scope of the new technology, digital cinema may be the biggest thing to happen to movies since the talkies.

For much more information on digital cinema, check out the links on the next page.

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