What is High Definition TV?

A high definition TV signal is transmitted in a 16:9 aspect ratio. 16:9 is also known as widescreen or letter box - like the screen in movie theatres. High definition TV has around four times as much picture detail compared to standard TV.

Who provides the service?

At the moment the key providers of High definition TV in the UK are Telewest (Now Virgin Media) and Sky and with more High Definition TV (HDTV) channels becoming available, it's important to understand what this all means.

Is Digital TV and High Definition TV the same thing?

Both standard definition and high definition TV signals are transmitted digitally. High definition TV is the top-level resolution offered but requires a specific decoder to unscramble the information.

What does resolution mean?

Standard television signals have a resolution of about 540 lines whereas high definition TV is at least 720 or 1080. This number represents the number of 'vertical' lines across the screen that make up the picture; the more lines the better the picture quality.

You will also see a letter after the resolution number, which is either an 'i' for interlaced or 'p' for progressing scanning. For example: 720p equates to 1280 horizontal lines X 720 vertical lines in a single whole frame (not made up of numerous scans from top to bottom as with traditional (interlaced) TV signals). This results in a smoother crisper image.

A signal transmitted as 1080i would in fact show 1920 horizontal lines with 1080 vertical with te images interlaced. It should be noted that a TV or minitor with 1080i capacity is required to see the best 'un-scaled' results.

The ultimate image resolution is currently 1080p but the High definition TV suppliers are not currently transmitting at the rate and there are very few projectors and players that can accomodate this at this time.

So what does all this really mean? - Projectors, Plasma and LCD screens accomodate one of these formats. The lower end cheaper models only support 720 vertical lines. If you can afford more, go for something that can support 1080i and you will get the best possible image when viewing High definition TV.

Do I really need High definition TV?

At the moment not all programming is offered in HD and there is an additional charge for High definition TV programming. You can get a brilliant picture with standard digital TV on a reasonably priced screen, although you will not get the 'HD' experience of rich deep images without it.

Do I have to subscribe to cable/satellite to get High definition TV?

At the moment, the only way to recieve regular high defination TV programmes is via Telewest (now Virgin Media) or Sky but there are some channels currently experiementing with high definition programmes transmitted to freeview boxes.

What do I need and what does it cost?

Sky HD

To recieve Sky's High definition TV service, you need a satellite dish and a Sky HD Box. You should also note that you will need a compaitble TV, such as plasma or LCD that is 'HD Ready' and it is recommended that your screen has at least one HDMI or DVI socket (as some older screens do not have this). At the moment you can connect a Sky HD box to your screen using using component video inputs but Sky are considering removing this ability from its future generation boxes. If you don't have HDMI sockets on your current HD Ready plasma or LCD screen you might want to consider subscribing to Sky now!

Sky customers currently pay £299 for an HD box plus a £10 per month additional subscription (on top of standard digital subscription costs). See www.sky.com for more details). Customers not taking a package of two or more Sky Premium channels will pay another £10 a month for Sky+ functionality.

Sky Channels with high definition TV

Sky currently transmit the following Sky channels:

Programmes are broadcast in either 720p or 1080i and your TV should be able to display both if you want the best picture quality.

Telewest/Virgin Media HD

Telewest's (now Virgin Media) high definition TV servive is now available to nearly five million homes in its catchment area. The content is not the same as that offered by Sky; there are no movie or sport based channels but Virgin Media does also have the BBC HD channel. Other High definition TV channels include arts and nature/wildlife material and has some exclusive Channel 4 programmes.

The plus side for Virgin Media is that High definition TV content is available at no extra cost to subsribers.

There are no up-front installation costs for new customers although existing customers must pay a one off charge of £50 - which is still cheaper than the £300 hardware costs charged by Sky who will hopefully take note!

Virgin Media also offer a great selection of programmes on demand:

• Over 500 films at your beck and call (£1.50 to £3.75 a go.)
• 1000 music videos, including concerts (from 20p a go.)
• Popular drama series, kids programmes, comedies and documentaries (Cost included).
• Their pick of last week's TV, for free.

Sky has just introdiced a similar on demand service for a limited number of programmes, but this does not currently compete with Virgin's service.

So who should I pick?

The following chart indicates a breakdown of the High definition TV services provided by each party:

SkyHD have the most HD and other channels to pick from and Virgin Media still have a way to go to catch up. However, SkyHD is certainly not a cheap option and Virgin Media's Video On Demand choices are brilliant compared to the slow starting Sky+ offering. There are certainly choices to consider when thinking about High definition TV.