High Definition
TV in the United Kingdom currently operates on a system called PAL which uses 576 vertical lines to build the on-screen picture. The image you see is broadcast in two parts; the odd numbers arrive first which are one, three and five etc followed by the even numbers 2, 4 and 6 etc. This happens faster than your eyes can see; this is called interlacing. HDTV also uses interlacing however it can also use a process called Progressive scanning which makes the on-screen image up in one pass – lines 1, 2, 3 etc.
This allows a very smooth representation of movement, which makes it ideal for fast moving sports such as football and formula one motor racing. There are two different HDTV formats. Interlacing is the technique used with the 1080 line HD system – hence the term 1080i. Progressive scanning uses a 720-line standard – hence the term 720p. Despite their apparent differences both methods give a viewing experience that is much more detailed than current TV transmissions.
Reassuringly for potential HD customers any TV that qualifies as being HD Ready and therefore is able to display the HD-Ready logo must be able to support both HD formats in addition to the standard definition broadcasts.
The 720p broadcast will most likely be used for sports coverage because of its smooth rendition of movement whilst the 1080i format is more likely to be used for wildlife documentaries and Hollywood films where the extra detail really shines through. The good news is that if you have a HD ready TV it will automatically switch to the format the program is being broadcast in saving you the need to switch to the right mode. Finally, the last great feature of HDTV is that the broadcasts are transmitted with multi-channel surround sound audio exactly as you can get with a DVD.
The HD Ready Logo
| When choosing your new television especially for HD programs you need to look for the HD Ready Logo. The TV set has to meet a number of strict criteria to qualify for the HD Ready Logo. These criteria include having a minimum of 720 physical lines, and being a widescreen TV. In addition, it must have the special HD connectors – DVI or HDMI. These two cables ensure the best possible picture quality. However, most importantly of all the set must support both the 720p and the 1080i broadcasts. Below is a quick guide to screen resolutions: |  |
PAL: 720 x 576 pixels
720p: 1280 x 720 pixels
1080i: 1920 x 1080 pixels
Understanding the Benefits of HD
To appreciate the total benefits of HDTV we need to look at how we currently watch standard definition (SD) TV. We take it for granted that our set-top boxes (STB) and DVD players are both digital devices we are therefore getting undiluted digital quality. However, that is not strictly true; both products convert their output to an analogue signal (read loss of quality) so that our conventional TV’s can display it. Of course, because the original signal is digital it looks a whole lot better than traditional analogue TV or VHS. However, if your TV could accept a digital feed directly without having to convert to analogue you would see a significant step up in quality. That is what an HDTV is capable of doing. So not only are you getting a much higher definition from a digital source you are also losing the analogue interference. The result is a viewing experience getting close to going to the cinema. There are two types of digital connection on an HD box – HDMI and DVI – and for a TV to be HD Ready it requires at least one of those connections. The same types of interface will also be included on future HD devices, such as high definition recorders. HDTV is the future of television viewing. Its clarity and sharpness of image leaves conventional TV’s pictures looking fuzzy and indistinct. Combine this with 5.1 surround sound audio and it makes for a truly great viewing experience.
Encoding Formats
There are currently two digital encoding formats being used for TV transmission, MPEG2 and its superior successor, MPEG 4.
MPEG2 is used by DVD as well as Freeview. It is a lossy compression standard, meaning some of the video source is removed to make the file smaller. This result is occasionally seeing blocky artifacts in the video file, particularly in high-speed motion scenes.
MPEG4, will be used by Sky fir its HDTV service, it is a more efficient compression format than MPEG2, although there is still some loss. As a result, it offers higher image quality at much smaller file sizes. The new HD set-top boxes will seamlessly handle both encoding formats.
HDTV Jargon Guide
Brightness: The brightness provided by LCD, Plasma or projector is measured in ANSI lumens. The higher the brightness the better the unit will perform in well-lit rooms. Low brightness may mean needing blinds or curtains being drawn and lights to be dimmed to achieve a bright projected image.
DLP: Digital Light Processor. A display device that reflects light on a dot-by-dot basis to create a high quality projected image.
DVI: Digital Video Interface. This cable provides high-bandwidth digital connection between the source (HDTV signal) and the display device (LCD, Plasma). DVi” cable carries a high quality digital picture but not audio. So an additional digital audio cable is required if you want sound out of your HDTV.
HDMI: High Definition Multimedia Interface. A high-bandwidth digital connection for both video and audio data. HDMI ensures the best quality video signal is sent from the source (HDTV signal) to the display (LCD, Plasma). This done by sending uncompressed video and multi-channel audio data to the display through a single cable. As this cable carries both audio and image signals, it is the preferred connection format.
HDCP: High Bandwidth Digital Content Protection is a copyright protection system that is incorporated into HD displays and receivers. This prevents unauthorised duplication and distribution of copyrighted content.
INTERLACE SCANNING: The system whereby the display (LCD, Plasma) shows every odd horizontal line in the scan then every even line in the second scan. This means the complete screen is shown every other scan. This happens so fast your eyes cannot detect it
LCD TV: Liquid Crystal Display. This is one form of flat-panel TV. They are made up of two transparent panels with a liquid crystal solution sandwiched between the two. Electric currents are passed through the liquid – this causes the crystals to line up so that light cannot pass through them. Each crystal acts as a shutter, allowing light to pass through or blocking it out. The pattern of transparent and dark crystals forms the image.
MPEG4: MPEG4 is a compression format that allows more data to be sent to the receiver in a reduced bandwidth.
PLASMA DISLAY: A type of thin visual display similar to LCD, however plasma panels can be created in larger sizes than an LCD. Plasma creates the picture by using a gas in a vacuum between two panels.
PROGRESSIVE SCANNING: This is based on all the horizontal lines being shown on the screen at the same time giving a much smoother image ideally suited to fast moving images (Motor racing, football matches).
RESOLUTION: The clarity and sharpness of the picture is referred to as resolution and is measured as the individual dots of colour that makes up the image. The higher the number, the truer the picture.
720p: This means the resolution of the TV picture is 720 horizontal lines the ‘p’ refers to progressive scanning.
1080i: This means the resolution of the picture is 1080 lines the ‘i’ refers to Interlaced scanning.
VIEWING ANGLE: The angle from which you watch the set varies immensely; therefore, viewing angles are important. A wide viewing angle ensures that the picture is visible from a greater range of positions. Normally represented by two figures, a viewing angle of 170° x 170° would indicate that the picture could be viewed from 170° both horizontally or vertically.
© AV Shopping.co.uk 2008
