High Definition - more pixels for your pound

What is it?

High Definition video means a video image with a higher-than-normal definition. So the small, coloured elements that make up the image are smaller and there are more of them. It's as simple as that. The driver is picture quality - the higher the definition, the clearer and sharper the image. The improvement in image quality is such that the famous beauties of television and cinema are said to be concerned that their few blemishes will become apparent. High definition signals are also highly preferable for very large televisions.

Nowadays, a "normal" video signal is regarded as the common-or-garden signal that generates a TV image. In Europe (and the rest of the PAL/SECAM world¹) this means 576 lines; in the USA (and the rest of the NTSC world²) televisions display 484-line images. Both the traditional systems are analogue, but are considered to have about 720 "columns", and so an overall resolution of 720×576 or 720×484. Regular DVDs are created to match these sizes. DVD players, VCRs and cable boxes send the humdrum analogue signals out over aerial coax, SCART leads and composite cables to the tube.

A High Definition video signal is many times more detailed than this. The television industry has standardised several possible resolutions and branded them "High Definition". Each offers grids of pixels- usually either 1280×720 or 1920×1080. They are known by the number of horizontal lines, and a letter indicating how the lines are displayed. The main ones being 720p, 1080p and 1080i. PAL and NTSC signals are sometimes called 576i and 484i to bring them into line with this convention.

More details please?

Both the normal NTSC and PAL/SECAM are "interlaced video", meaning that the odd numbered lines of each frame are displayed first (top-to-bottom), and then the even numbered lines (bottom-to-top). The image can be updated when the beam illuminating each line changes direction at the bottom of the screen. In standard high definition signals, the letter "i" after the line-count indicates an interlaced signal. High definition signals can also be "progressive", meaning that the lines are displayed in a straightforward series, from top to bottom. These signals are marked with a "p".

In some consumer taste-tests, 720p was preferred to 1080i, even though it has a much lower resolution³- progressive images flicker less. In theory, because the image may be updated twice as often (at the expense of horizontal resolution), interlaced images may capture the rapid camera movement of fast-paced sporting events more smoothly.

Unlike traditional analogue signals, the shape or "aspect ratio" of the display suits widescreen, since it has square pixels in the familiar 16:9 ratio. PAL or NTSC signals can be squished or stretched to give a widescreen image, but in the HD world, widescreen is the starting assumption.

Where does it come from?

The consumer cannot just buy a high definition television and hope for the best. He'll need to know where he's going to get a signal from. Normal NTSC and PAL broadcasters, DVD players, VCRs, and games consoles will continue to splutter out a few hundred lines, no matter how fancy the TV is. A large, HDTV may even show up the unpleasant artifacts of a compressed image more clearly than a standard telly. There is a lot more information in a high definition signal than in a normal one. An NTSC frame has under 350,000 pixels in it; a 1080i HD frame has over 2 million. Content providers have had to re-tool their entire production line from cameras to editing facilities, storage media, broadcast equipment, interconnecting distribution networks and cabling- you name it. The home user will need mirror images of these bits of kit to run his new toy; a new TV, a new DVD player (but which type?), new set-top boxes, and new HDMI cables (which are more like delicate DVI monitor cables than the brutish SCART leads the PAL world is used to). A useful half-way measure might be a DVD player with an upscaler- a component that blows up a standard-def DVD so that it has the right number of pixels for an HD screen; these look surprisingly good.

Two alternative DVD formats are available which offer the extra capacity that a high definition publication demands- HD DVD from Toshiba and Blu-ray from Sony. Both standards offer up to 1080p playback. A new format war is threatened, and it's not clear whether one side will win, or both will co-exist. Naturally enough, a regular DVD player will not play either format.

The Microsoft XBox 360 and Sony Playstation 3 games consoles can output games in HD; and so can the current generation of PC video cards.

Television content providers are also upping their game and upping their definition; but the most expensive productions are, like feature films, already shot on 16 or 35mm film. These productions can be converted to a high definition signal and issued on one of the new DVD formats or broadcast in HD with the minimum of fuss.

Broadcasters are catching up with HD video technology. In the UK, the BSkyB satellite broadcaster leads the HD field and offers a range of movies, drama serials and sporting fixtures in HD, although it's only a fraction of their output. Telewest offer a similar line-up via cable. Both of those broadcasters run "BBC HD", a showcase for all the HD productions the corporation has been quietly recording for the last year or so. In the US, Mark Cuban's HDnet, a national HD broadcaster were also quick off the mark.

The terrestrial broadcast market in the UK is going through a transition; analogue transmissions around the country are being shut down, region-by-region, with London being last to transition to the "Freeview" digital service in 2012. But Freeview is a standard PAL service, with an emphasis on multi-channel broadcasting, rather than picture quality. The public tend to conflate "digital" with "quality" and hence with "high definition", but this is not the case for Freeview, which is basically 576i.

There currently isn't a great deal of free capacity in the television frequency bands to introduce a high definition terrestrial service. Once the analogue signal is shut off, more spectrum will become available, which could in principle offer a multi-channel HD service. Indeed trials of "Freeview HD" are underway. But current plans are to auction the new spectrum off to the highest bidder, who may use it for something completely different. Current terrestrial broadcasters (BBC, Channel 4, ITV and Channel 5) have recently formed a campaign group called "HDforAll" to lobby for guaranteed access to the vacated spectrum for terrestrial HD broadcasts.

What's the catch?

It's HDCP.

The content industry has learned its lesson from Napster and piracy in general- digital copies can be transmitted effortlessly and don't lose quality. In preparing the HD standard, they've come up with a way for each part of the system to enquire about the capabilities of each other part- High Definition Copy Protection or HDCP. HD content can be encrypted, and a playback device will not decrypt it at full quality unless it is convinced you're not going to make a duplicate. An HD DVD player can therefore use the HDCP protocol over a standard HDMI cable to ask whether it's connected to a TV (fine!) or a recording device (not fine!).

The HD standard requires a playback device to drop its output quality in the presence of recording media or rights-infringing equipment. A 720p signal might become 480i; and a 1080i image would drop to the otherwise-unseen 540i. This is an entirely artificial limitation, designed to ensure that "home-taping" will always look worse than original content. It's not clear how subtle HDCP's idea of "fair use" or "fair dealing" is. Strict (some would say over-zealous) adherence to similar requirement is at the heart of Windows Vista's notorious copy protection policy.

Currently, not every device has HDCP, but soon more and more content will require it. HDCP can be seen as part of a general trend towards Digital Rights Management or DRM. There are some signs at the time of writing that DRM might be beginning to die out as far as digital music is concerned- but only time will tell. In HDCP, high definition video systems come with a clever, interoperable DRM system that at least allows you to make copies, if of restricted quality.

A personal view

I've seen the usual demo-reels of HD content in the shops, and it is a definite improvement over the TV images we've grown accustomed to. The enhanced detail draws you in, and there seems to be richer colours and higher contrast too.

More broadly, though, television isn't really very good, is it? With a few notable exceptions it feels like a medium past its prime. I mean there's not much worth watching as it is. It's possible that the advent of high definition images will lead the content providers away from the horrid "reality television" shows they've been excreting lately towards epic, Ben Hur-style productions. But I doubt it. My media consumption tends more and more towards recorded music, thought-provoking radio and the Internet; television, both broadcast and on DVD is being squeezed out of my life. Viewership figures are drifting downwards, downwards across channels. Will widespread HD availability buck audience trends, or will future generations of consumers look back on high definition broadcasts as television's last gasp?


As a youth, I had a TV in my bedroom with a 3-inch, black and white screen. I tuned it in manually with a little dial. It had an integral audio cassette deck! The image quality was lamentable, but it didn't matter. I enjoyed eight years worth of comedy shows and movies on that little set- after a minute or two's viewing I became fully acclimatised to the shaky, snowy picture and began to enjoy the programming. Perhaps the "wow" factor of HD would not last much longer than the "ow" factor of my old set?

¹ - Europe, Africa, Most of Asia and South America.

² - North and Central America, parts of South America, Japan and a few other isolated spots.

³ - Mind you, surveys have also shown than many proud owners of HDTVs are pleased with improved picture quality, even though they're only using them to view normal definition content. The things people can convince themselves of when they have a £1000 outlay to justify!


  • HD TV in the UK; Register special report - http://www.reghardware.co.uk/2006/12/08/hd_tv_uk_guide_updated/
  • PAL, http://en.wikipedia.org/wiki/PAL
  • NTSC, http://en.wikipedia.org/wiki/
  • Blu-ray Disc, http://en.wikipedia.org/wiki/Blu-ray_Disc
  • HDforAll, http://www.hdforall.org.uk/
  • HD DVD, http://en.wikipedia.org/wiki/HD_DVD
  • Time Magazine - For TV Stars, High Def is Dicey (On how some celebrities don't look so hawt when described by millions of extra pixels.), http://www.time.com/time/magazine/article/0,9171,993791,00.html
  • A Freeview HD trailist tells all: http://www.hdtvuk.tv/2006/06/a_freeview_hd_t.html

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