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Technique

Le présent article n'est pas disponible en Français
April 2008

Crisper, clearer, sharper, brighter. High definition (HD) has transformed video in the same way that colour transformed photography. We examine the benefits – and the challenges – HD offers today’s camcorder users.

Picture quality never stands still. In both photography and video, there is a constant quest to create images that are more detailed, more vibrant and more lifelike. For a long time, the broadcasting and video worlds operated in standard definition, using either 625- or 525-line systems. But now, the video world is rapidly moving towards the high definition as HD equipment is now routinely installed in many broadcasting suites and studios, and HD-ready displays, along with HD-compatible games consoles, camcorders and video players, are flooding into households.

In the same way that everyone expects televisions and camcorders to offer colour pictures, so more and more consumers are expecting on-screen images to be in HD. What is more, broadcasters are increasingly demanding that footage is now shot in HD and it’s rare that a major TV production is shot in anything else these days. It makes good sense, because HD images can be down-converted to SD, and at the same time, HD footage is ready for the time when HD broadcasting becomes the norm. As a result, filmmakers, documentary makers, news gatherers and enthusiasts are investing in HD camcorders.

Naturally, HD equipment commands a premium over standard definition products and until recently, professional-quality HD camcorder prices were beyond the means of most camcorder users. But a new generation of affordable, high-specification HD camcorders – like the XH G1 and XH A1 – have brought HD into the hands of many. What is more, affordability does not mean having to make compromises when it comes to performance, functionality or versatility.

HDV format

Canon’s HD camcorders use the HDV format, a tape-based system which comes in two forms: 720p and 1080i. The former displays 720 scanning lines with progressive scanning, but most HD broadcasts, HD videos and HD camcorders (including Canon’s) use a 1080i system, which displays 1080 scanning lines that are interlaced. In order to capture HD images, high resolution CCDs are required and Canon’s HD camcorders are equipped with three 1/3-inch 1.67 megapixel CCDs for this purpose.

HDV 1080i images are recorded on tape in the form of 1440 x 1080 pixels in a 1.33:1 aspect ratio, but can be displayed by an HDTV monitor as 1920 x 1080 pixels in 16:9 aspect ratio. This means that each HD frame is composed of more than two million pixels or roughly four times more information than a standard definition display. As a result, fine detail that is normally lost in standard definition images (such as skin texture or individual blades of grass) can be captured and displayed by a good HD system. Some HD camcorders – such as those from Canon – also offer 25F (frame) shooting, a system specially developed by Canon to give video footage a more film-like appearance.

Recording HD images generates a large amount of data, and when shooting in HDV’s 1080i mode, the data rate is 25Mbps. This massive amount of data demands huge processing power and Canon’s HD camcorders use a DIGIC DV II processor to reduce noise and enhance colour reproduction.

In order to reduce the amount of data that needs to be recorded, processed and stored, the HDV format uses MPEG-2 video compression to remove redundant picture information. MPEG-2 is a lossy compression system which arranges frames into groups of 12 or 15 and then uses both intra-frame and inter-frame compression techniques to reduce the amount of data. This enables up to 80 minutes of HD video to be stored on a MiniDV cassette, using 6.35mm metal tape.

MPEG-2 is a highly efficient system, but the nature of the compression process means that editing native HDV footage is a challenge, because splicing between frames causes some disruption and distortion at the edit point. But there are ways around this, for example, by decompressing and then recompressing an HDV frame group. Another way is to transcode the HDV footage using an intermediate codec, which allows each frame to be decoded and displayed independently. HDV also compresses the audio, using high quality MPEG-1 Layer II compression, with a data rate of 384kbps.

HDV footage can be easily transferred from a camcorder to a PC using an IEEE 1394 interface (also known as Firewire), although some HD camcorders – such as Canon’s XL H1 and XH G1 – also offer a High Definition Serial Digital Interface (HD-SDI) output, which can handle both compressed and uncompressed video (at full 1920 x 1080 resolution with 4:2:2 chroma subsampling), and is widely used by the broadcasting industry.

Shooting in HD demands higher production values and any flaws in lighting, colour balance or focusing can be mercilessly revealed on-screen. But set against this is the giant leap forward HD offers in terms of creativity, picture quality and sheer viewing enjoyment.

To find out more about the Canon video products mentioned in this article or to try out or purchase Canon video products, contact your nearest Canon video dealer. For contact details just click here.