Laptops	TV	Projectors	Digital Cameras	Camcorders	DVD Players	Game Consoles
Consumer Electronics with High Potential

Mark it:

Web	www.zettavolt.co.uk

High Definition Television (HDTV)

High Definition is a new development in TV and video that provides pictures which improve over the standards which have been in use for the last 40 years. The most significant improvement is better image resolution for more detail. This is acheived by using more lines and pixels to make up the image. The traditional TV image (now known as standard definition) is made up of 480 lines in the US or 576 lines in Europe, but the new standards push that to 720 lines or even 1080 lines. These changes are also accompanied by higher specifications for colour, frame rates and surround sound.

To receive the Sky service you need a Sky HD box, satellite dish and SKY subscription. Unfortuneatly it is a very expensive service which will cost at least ?299 for the box and setup and ?642 a year subscription if you want all the HD channels. For the Virgin media service you need to live in an area with their cable connection and you need a V+ box. This is much cheaper but so far the HD choice is limited to BBC and some on-demand films.

Ideally we would like to be able to pick up HD via traditional network television but that is not happening. Although a trial of HD Terrestrial transmissions has been taking place in London, it is unlikely that this will be continued or extended. There are some other alternatives for HD such as the Belgian satellite channel EURO1080, but the most promising prospect for HD content is online-TV which will be provided via the internet. If you want something simpler, you can also buy an HD-DVD player and watch films from HD-DVD disk.

HDTV resolution standards

To understand HDTV you need to understand something of the different HD standards used. The main standards that you will hear about are 720p, 1080i and 1080p. 720p uses a widescreen pixel grid of 1280 by 720. The p stands for progressive, which means that every line in a frame is scanned for each image field. This differs from the old video system known as interlaced where a frame is scanned in two successive fields each consisting of alternate lines of the frame. The progressive standard is much better especially with fast action images so it is preferred for sports. The 1080i and 1080p standards use 1920 by 1080 pixels. The difference between the two is that the 1080i standard is interlaced while 1080p is progressive. The standards used for broadcast TV are 720p and 1080i, with 720p being more common in the US and 1080i being more common in Europe. 1080p which is sometimes known as Full HD is used for non-broadcast video such as HD-DVD or internet downloads.

Faster Frame Rates

The frame rates for the progressive HDTV standards are in principle twice what was available with the old interlaced standards. 50Hz is now used in Europe and 60Hz in the US. Films are traditionally recorded at 24 frames per second and until that changes we will not see smoother movies in HDTV, but live sports action is already being broadcast at the higher frame rates for improved action sequences. There is an ongoing problem with the need to transform between the different frame rates and that can lead to some jerky effects. For example, coverage of a sports event in the US is likely to be captured at 60Hz so to show it in Europe where the stadard is 50 Hz the broadcaster may just remove every sixth frame. The better HDTV sets have electronics that can smooth out the movement. Some even use motion compensation methods to interpolate between frames when the video is derived from film source. The next generation of displays offers the capability to refresh at frame rates up to 120Hz which is more than adequate for even the fastest action sequences.

Digital Television (DTV)

Traditional TV transmissions came in analogue form so that each line was traced out in the signal as a varying strength exactly as it had to be displayed. Modern TV and HDTV in particlualr is always delivered in digital form, i.e as streams of binary data. One advantage of a digital signal is that there is normally no loss of information during transmission or recording, but to keep the amount of data within the necessary broadcast bandwidth it must be compressed and that means some loss of information. Standard Digital television is compressed using MPEG-2 but HDTV is often compressed using the newer MPEG-4 which has allows higher compression ratios. Compression always reduces the quality of the picture and the amount of loss can be controlled by the originator of the signal. If it is compressed too much then the viewer will start to notice loss of quality in the form of artifacts such as pixelation. If a broadcaster wants to squeeze more channels into the limited bandwidth they have available they may be tempted to cut the quality down. Even if a program is broadcast in 1080i the compression may reduce the amount of detail in the image so that it is no better than a lower standard such as 720p. This is less of a problem with recorded media such as HD-DVD or internet downloads so ultimately these could become the media of choice for HDTV films.

HD Ready Display Technologies

With HDTV comes a new range of television display technologies which are very different from the old cathode Ray Tube (CRT) sets. You have the option of flat screen TVs or projectors that use a variety of technologies. For the majority of viewers the main choice will be between LCD or Plasma screens. LCD has proven to be the easier type of display to manufacture at high resolutions. Even QuadHD LCD displays with 3840 x 2160 pixels are available. That is the equivlent to four 1080p screens in one. The problem for LCD producers is that LCD screens at high resolution make no sense unless either the viewer is very close or the display is very big, and it has proven difficult and expensive to manufacture large 46 inch pus LCD panels. The developers of plasma screesn have faced the opposite problem. They have found it hard to achieve Full HD 1080p resolution and the panels are diffcult to make at the smaller sizes around 32 inch that most people are used to having in their living rooms.

There are other advantages and disadvantages between the two technologies. If you want good screen response times for smooth action then Plasma is better. Plasma also has better contrast ratio and colour range so overall the plasma screen is the ultimate choice if you can accomodate a large screen and want the very best picture quality. However, plasma screens reflect more light back so they are not as clear as LCD in a bright room, they also need more power and sometimes need a noisy cooling fan to avoid overheating. They are also prone to burn-in so you have to be careful what you do with them for the first few hundred hours of running.

As time has progressed these limitations have diminished for each. Large LCD screens with very good images and response times are available. Likewise, plasma screens can be made at the sizes and resolutions that the market needs. When buying it is best to compare the two together and choose on the basis of specification and test comparisons.

Surround Sound

You will not get the full HDTV experience unless you also have good quality surround sound. Audio for up to eight speakers is becoming common place and the signal is encoded at 24 bits giving much better clarity and dynamic range than the 16 bit standards used on CD. Dolby TrueHD is the leading standard but it is not yet commonly available.

Connectors and Copy Protection

When buying any HDTV equipment it is important to check which connectors it supports and how many. The most common standard connector for HDTV is HDMI (High-Definition Multimedia Interface) which supports HDTV standards up to 1080p at 60 Hz and TrueHd sound. It also includes the HDCP copy protection standard which is important since a lot of HDTV content is likely to use copy protection. In short, if all yout HDTV devices interconnect with HDMI then you are in good shape.

An alternative connector which is common on computers is DVI-D or DVI-I which can alos include the essential copy protection standards. However, this is not mandatory so of you use DVI you need to make sure that the right standards are supported at both ends of the cable. If not your signal could be automatically downgraded to a lower standard and the only indication will be a poorer quality picture. For these reasons the use of HDMI is preferrable.

HD-DVD and Blu-Ray

The media industry is marketing two competing systems to replace DVD for HDTV movies. HD-DVD and Blu-Ray are incompatible and are supported by different manufacturers and film studios. This means that it is not possible to buy one player that is sure to be able to play all films, unless it is an expensive dual format player. While this is clearly a problem and has been the subject of much dismay and critcism from consumers, it is also true that the competition between the owners of the standards has helped accelerate the speed at which these players have been brought to market and has kept the cost low. It is still too early to know which of the two standards will win. It is even possible that both formats will die before their war is won because interent downloads to hard-disk may make them obsolete.