High definition TV explainedGet yourself HD-ready

HD-ready TV

First, you need a TV that’s ‘HD-ready’. This means the TV has the minimum requirements necessary to receive and display the higher resolution HD picture. Most new large-screen TVs in the UK are now HD-ready.

Which? tests TVs continuously so read our TV reviews to find a Which? Best Buy that's right for you.

The technical bit

HDTV pictures come in two main formats – 1080i and 1080p – depending on the number of horizontal lines that make up the picture and the way they’re broadcast. All HD-ready TVs can display 1080i – and in effect there’s not much difference between the two.

HDTV is broadcast in 1080i. This is made of 1080 lines – the ‘i’ means the lines are not scanned 1 after another, but ‘interlaced’ so all even-numbered lines are scanned first and then odd numbers. The two combine to make a picture.

A 1080p image is made up of 1080 lines scanned one after another, and pictures are even sharper and more detailed, but this improvement is quite subtle. This system isn't used by broadcasters, but is used by the new generation of high-definition Blu-ray DVD players, but these players also output 1080i if required. a 1080p picture is more detailed and realistic than a 1080i image - but the effect is quite subtle.

DVI input

The humble Scart lead won’t cope with HD signals so a new type of interface and lead has been created called HDMI.

To get HD, your TV will have to have an HDMI or DVI socket and be compatible with a copyright protection system called HDCP, as the movie industry is concerned that people will start to pirate high quality transmissions.

The HD-ready label ensures compatibility with the HDCP system.

HD-ready and HD-ready 1080p

The official logo

The HD-ready label means the LCD or plasma TV has the minimum screen resolution (of at least 720 horizontal lines) and digital sockets (HDMI or DVI) to receive and display a 1080i HD picture - so they're perfect for watching HDTV from Sky, Virgin or Freesat. Most new HD-ready sets will also support the 1080p HD signal. If the TV does not support 1080p it simply switches to 1080i.

The relatively new HD-ready 1080p logo from EICTA (the same people behind HD-ready ) means the LCD or plasma TV can process a 1080p signal but also has a high screen resolution of 1080 horizontal lines (1920x1080). In theory this should mean even better HD pictures, but in practice the quality of the TV picture has alot more to do with the picture processing software that powers the set, rather than just the resolution of the screen.For instance, many of our Best Buy Panasonic TVs have a relatively low screen resolution but boast fantastic pictures.

Similar-sounding and -looking logos such as, HD Full, 1080HD or 1080HD-ready are also commonplace, but exact meanings can differ between manufacturers. 

24fps.

The whole 1080i versus 1080p question is further complicated by something called 24fps (frames per second). It's not unusual for new TVs to sport logos boasting 1080/24 compatibility. This simply means that the TV can process the 1080p signal and display it on screen at 24 frames per second. The HD-ready 1080p logo is a guarantee of this but most new HD-ready sets will process 1080/24 too.

1080/24 can become an issue if you want to watch Blu-ray movies on your TV. The high-definition discs are recorded at 24 frames per second , rather than the traditional European speed of 25fps. If the output from the player and the refresh rate on the TV screen don't match the result can be juddery movements on camera-panning or fast motion scenes.