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How Digital Cinema Works


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.