Behind the DV technology

Jan Ozer ZDNet US

Published: 10 Jan 2003

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So, what is digital video? Technically, the DV format is a sequence of frames compressed to a data rate of 25Mbps, using a technology called Motion JPEG. Despite the format difference, however, DV cameras work like analogue cameras to a certain degree. They use lenses to focus on an image, then use charge-coupled devices, or CCDs, to convert the image to electronic signals.

Demystifying DV

Here's the difference between digital and analogue cameras: rather than storing a video frame on tape in analogue format, as a VHS or Hi8 camera would, DV cameras convert the image to zeros and ones, compress it to DV format, and then store the digital file. This compression method greatly reduces the generation loss associated with storing an image on tape, which means that digital video offers higher quality both when you compress the video and when you copy it later. In addition, DV stores a higher-quality signal than most consumer analogue formats (500 lines of resolution compared to VHS's 240), which further improves comparative image clarity and detail. Translation: you see crisper images and more accurate colours.

FireWire: camera to computer, in a jiffy

Digital video also makes transferring video to your computer much simpler. Virtually all DV cameras come equipped with FireWire (IEEE 1394) compatibility so that you can easily transfer DV files to any computer with a FireWire port and the appropriate software. Most video-editing software can detect scene changes by analysing the time- and date-code data included on DV tapes and can automatically break your video into different scenes, making it easier to find specific segments of your finished video.

DV flavours

As with any burgeoning technology, digital video comes in several styles. MiniDV cameras store data on a tape cartridge that's about the size of a box of matches. Digital8 cameras store DV-formatted video on DV Hi8 tapes and can read analogue Hi8 tapes as well. You'll also see names such as DVCam and DVCPRO, which are higher-end formats used in professional cameras. A more recent format called MicroMV isn't digital video at all but an MPEG-2-based format stored on even smaller cassettes than those used by MiniDV cameras. In this article, we'll focus on MiniDV and Digital8 cameras, since those formats comprise the bulk of the cameras sold into consumer and corporate markets.

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