Articles and whitepapers

What is HDTV? (3/10/2005)

By Toby Pearce, Touch of a Button

HDTV (High Definition TV) is the future of television broadcast and should be top of the list for any audio visual custom installation. HDTV is as significant an improvement in viewing pleasure as the transition from VHS to DVD. It represents a step change in picture quality, offering greater depth and tone of colours and textures, and delivering a home viewing experience similar to that in cinemas.

NEC HD ready TV

The market for HDTV is already a reality in countries such as the United States, Japan, Canada, Australia and South Korea. In Europe, the Belgian broadcaster HD1 has been airing HD broadcasts since 2004. German and French broadcasters are launching a number of HD services in 2005, BSkyB plans to start HD broadcasting in 2006, and the BBC intends to produce all of its content in HD by 2010.

The path to HDTV

At present, we can receive two forms of TV broadcast, namely analogue and digital. Analogue TV has been with us since the 1930's, and with its signature 'ghostly' on-screen images, will be fading away for good in the UK by 2012.

Analogue television uses a technique called 'interlaced' scanning. The television picture is made up of 25 frames per second, with each frame comprising 625 lines. The frame is actually made of two fields. For the first field, the odd numbered lines are beamed onto the screen, then for the second field, all of the even numbered lines are beamed onto the screen. Interlacing works fine on small screens, but with larger screens, the scan lines become more visible and the interlacing system creates unwanted artefacts.

Computer screens on the other hand, use a technique called 'progressive' scanning whereby the frame is made up in one go by beaming each line sequentially, i.e. line 1, followed by line 2, then line 3 etc.

Both interlaced and progressive scanning are used with digital television, as are a variety of line resolutions ranging from 480 to 720 and 1080 lines, aspect ratios ranging from 1:1 (square) to 4:3 (standard TV) and 16:9 (widescreen TV), and different frame rates e.g. 720/50 (720 lines using 50 frames per second) and 1080/25 (1080 lines using 25 frames per second).

In the US, digital television currently comes in three guises, namely standard definition TV (SDTV), enhanced definition TV (EDTV), and high definition (HDTV). SDTV typically uses 480i (480 lines interlaced), offers a picture quality at least as good as analogue, and also includes digital surround sound. EDTV typically uses 480p (480 progressive lines), and also offers digital audio. It has a much crisper image than SDTV, but is not as clear as HDTV. HDTV is the most superior video picture available in digital television, and has at least twice the resolution of SDTV.

In the US, there is a wide variety of formats in use for broadcasting digital television, and is it up to the broadcasters to choose which format they broadcast in. For high definition, broadcasters such as Fox, ABC, and ESPN broadcast 720p content, whereas NBC and CBS broadcast 1080i. In Europe, there is as yet no consensus. Some interested parties are pushing for 1080i lines, whereas others are championing 720p.

HDTV specifications

With HDTV becoming more widespread across Europe, television broadcasters must work together to set a uniform standard of presentation. Although a single broadcasting standard has yet to be agreed, Europe's national broadcasters - members of the European Broadcasting Union (EBU) - are at least supporting the 'HD ready' logo.

The HD ready logo

The aim of the HD ready logo is to give consumers the assurance that displays from different manufacturers are fully compliant with accepted technical standards of HD broadcasts. The HD ready logo can only be attached to displays that meet the following conditions:

* have a minimum of 720 horizontal lines;
* accept HD inputs via analogue component (YPbPr), and DVI or HDMI;
* can accept 720p/50, 720p/60, 1080i/25 and 1080i/30 inputs;
* the DVI or HDMI input supports content protection (HDCP).

A DVI (Digital Video Interface) makes the digital to digital connection (video only) between your video source, such as set-top box or DVD player, and the HDTV screen. An HDMI (High-Definition Multimedia Interface) is similar, but also supports audio.

HDCP (High-Bandwidth Digital Content Protection) was created by Intel, and is used with HDTV signals over DVI and HDMI connections to prevent unauthorised duplication of copyrighted material.

If you want true HDTV performance however, you need to take into consideration more than the just the screen. You must ensure that the entire signal path is HDTV compliant. If any components are not, there will be a weak link and a loss of quality.

High Definition TVs

For most of the branded manufacturers, expect to pay around GBP2000 for a 42" HDTV plasma. LCD (Liquid Crystal Diode) and DLP (Digital Light Processor) screens are also available, and rear projection screens offer the best picture quality per cm2.

The Pioneer PURE Vision Black HD ready plasma TV

Given the speed of progress in this technology, a sore point is raised. Nearly 90% of plasma and LCD TV screens purchased in the last five years will not meet the minimum requirements to be HD ready. That said, if you want a bargain you can now pick up non-HDTV compliant plasma and LCD screens at rock bottom prices.

Advice on purchasing an HDTV screen

Buying an HDTV is far more complicated than a standard CRT. You can choose between a plasma, LCD or DLP, and a range of sizes, so ensure you choose the most favourable option for the size of your room. Connectivity is also vital, as mentioned previously, HDTV is supported by DVI and HDMI, so ensure that whatever equipment you wish to use in conjunction with the screen, has the correct connections. And for those interested in bargains, the best deals are often found with 'unbranded' screens that offer as good quality as the well known ones, but at a considerable discount.

Toby Pearce is the Operations Manager for Touch of a Button, supplier of affordable, custom smart home, design and installation services.

www.TouchofaButton.co.uk