Techincal Answers - Displays

Its no use having DVD movies or videos if you no way of viewing them. Therefore you will need some form of display device. This article in out How 2 section will describe how these devices work, and how to connect them to your home cinema.

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Display Types

There are a number of different display technologies this section will describe the how each works and the advantages of each type:

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Cathode Ray Tube (CRT) Televisions

Television

How it works

This is the most common type of television and it is also the cheapest. The television works by sending a ray of light produced by a cathode towards a phosphorus coated screen. This ray forms a point of light, that is then moved using magnets to form a scanning line. The line scans down the length of the screen about 60 times a second. Each scan paints a picture on the screen, which is then changed with each subsequent set of scans. When a picture changes at sixty times a second the human eye is fooled into thinks the image is actually moving, and so the image on the television appears to move. Colour televisions use three coloured rays (red, green, and blue) and a focusing mesh to provide a colour picture.

CRT Televisions come in a wide variety of sizes, from about 5 inch screens right up to 32 or so inches. It is worth noting that screen size is measured diagonally across the screen, and that due to screen curvature the visual size of a screen is usually less than the specified size.

Verdict

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Liquid Crystal Displays (LCD)

LCD

How it works

These displays work by applying an electrical current to various points in a chemical coating in a transparent layered sandwich. Early displays were pretty imprecise due to the difficulty delivering the voltage to precisely the correct spot cause ghosting when displaying quick movement. However new displays uses tiny embedded transistors to fix this problems (these screens are called TFT displays). Splitting each point (or pixel) on the display into three coloured sub-points (red, green, and blue) forms a coloured display.

LCD screens can come in just about any size, however the larger the screen the higher chance that some of the points on the screen will not work. This makes it very difficult to manufacture very large screens.

Verdict

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Projection Televisions

Projection Televisions

How it works

These televisions work by using a light source to project a picture from a special small CRT or LCD through a magnifying lens onto a screen. The projected image is usually on the back of the screen and this is called rear projection. There are more advanced projection televisions that do not use a CRT or LCD but special reflective microchips; these apparently have a much better picture quality.

This type of television can be very big indeed. Most units are of forty inches or more. However the technology is not appropriate for use in small sets.

Verdict

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Projectors

LCD

How it works

Like Projection televisions, video projectors use a light source to project an image from a LCD or CRT through a lens. However unlike Projection televisions they require a separate screen. There are two main types of projector, those that use three separate coloured images and lens to create a image, and those that use a colour LCD through one lens to form an image.

Because the screens are separate they need to be place a distance away from the projector. This means that the image size is variable but can be anything up the size of a cinema screen.

Verdict

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World Television formats

When a signal is received by a television it is displayed in a specific format. This format determines the number of times a second that the screen is refreshed and the number of scan lines that form the picture. Just to confuse things there are three different and incompatible television formats. These are

Format: NTSC PAL SECAM
Name: National Television System Committee Phase Alternating Line Sequential Couleur Avec Memoire
Scan Lines: 525 lines 625 lines 625 lines
Refresh: 60 frames per second 50 frames per second 50 frames per second

The following table lists which countries use which format:

NTSC PAL SECAM
Antigua, Bahamas, Barbados, Belize, Bermuda, Bolivia, Burma, Cambodia, Canada, Chile, Colombia, Costa Rica, Cuba, Dominica, Dominican Republic, Ecuador, El Salvador, Greenland, Guam, Guatemala, Haiti, Honduras, Jamaica, Japan, South Korea, Mexico, Nicaragua, Panama, Peru, Puerto Rico, Saipan, Samoa, Surinam, Taiwan, Tobago, Trinidad, United States, Venezuela, Virgin Islands Afghanistan, Algeria, Argentina, Australia, Austria, Bahrain, Bangladesh, Belgium, Brazil, Brunei, Canary Islands, China, Cyprus, Czech Republic, Denmark, Fiji, Finland, Germany, Gibraltar, Ghana, Hong Kong, Hungary, Iceland, India, Indonesia, Ireland, Israel, Italy, Jordan, Kenya, North Korea, Kuwait, Liberia, Luxembourg, Malaysia, Malta, Monaco, Netherlands, New Guinea, New Zealand, Nigeria, Norway, Oman, Pakistan, Paraguay, Poland, Portugal, Qatar, Romania, Saudi Arabia, Sierra Leone, Singapore, South Africa, Spain, Sri Lanka, Sudan, Swaziland, Sweden, Switzerland, Tanzania, Thailand, Turkey, Uganda, United Arab Emirates, United Kingdom, Uruguay, Yemen, Yugoslavia, Zambia, Zimbabwe Albania, Benin, Bulgaria, Congo, Czech Republic, Djibouti, Egypt, France, Gabon, Gambia, Greece, Guadeloupe, Guyana, Haiti, Iran, Iraq, Ivory Coast, Lebanon, Libya, Madagascar, Martinique, Mauritius, Monaco, Mongolia, Morocco, New Caledonia, Niger, Poland, Romania, Russia Saudi Arabia, Senegal, Syria, Tahiti, Togo, Tunisia, Viet Nam, Zaire

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DVD Compatibility

These television formats effect not only television broadcast signals but also recorded media like DVD and video. This means that a NTSC encoded DVD would not display properly on a PAL television set.

This is a problem if you have a multi-region DVD player and want to play DVD's from region 1. Fortunately most modern televisions are capable of displaying pictures from any television format. However if you are intending to watch region 1 DVD 's it is worth checking out your television first.

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Screen Ratios

You may have noticed in our reviews that we give the picture ratio 4:3 or 16:9 or some such. What is this all about? Well consider the shape of an old-fashioned television screen it is quite square. Compare this to the shape of the average cinema screen, and you will find the cinema screen is much more rectangular. This difference in screen sizes means that television programs and film have different screen ratios. There are four commonly used screen ratios, and the following sections will explain these further:

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4 : 3 Full Screen

4:3 Full Screen

The screen ratio of the average television (not wide screen televisions) is four units in length against three units in height (4:3). This is the shortest screen length to height.

The effect of this is that to view a film on television a certain amount of the sides of the picture has to be cropped (a process called pan and scan). This usually is Ok as most films concentrate the action in the centre of the screen, but you still don't get to see the film as it was originally envisaged. Most television programs are still filmed in this ratio.

Full screen televisions can view films broadcast in other ratios. When this happens black lines are displayed above and beneath the picture, thus shrinking the picture to fit.

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16 : 9 Widescreen

16:9 Widescreen

In the last few years widescren televisions have started to appear. These are more oblong that the original televisions and have a screen ratio of 16:9. It must be noted that this ratio is still not narrow enough to view many films so a small amount of cropping is still required.

The majority of televisions sold in the UK are now of this ratio, and more UK produced television progams are widescreen. However this type of television is not as popular in the US as many people there are waiting for high definition television before deciding to upgrade. This is less of an issue in the UK as PAL (due to the increased number of scan lines) delivers a better picture quality than NTSC, so the UK has purchased the new widescreen televisions..

Wide screen televisions can view pictures broadcast in 4:3 ratio. They usually have a special 4:3 mode, which places black lines down either side of the screen thus maintaining the original aspect ratio. This 4:3 mode is automatic on some televisions.

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1.85 : 1

1.85:1

This ratio is extremely close to 16:9 and is often quoted as widescreen. The difference is too small to worry about.



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2.35 : 1

2.35:1

Many cinema films are this ratio and certain films retain it for broadcast or for the DVD. This ratio is wider and narrower than widescreen televisions, although it is possible to watch these films on the TVs as black bands are placed above and beneath the picture. It must be noted that full screen televisions will also display these films but the picture size will be reduced to fit the screen.

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Anamorphic

You may see a picture listed as Anamorphic, so what is it and is it a good thing? Put simply Anamorphic pictures use extra information from the space used by the black bars above and below the picture to enhance the picture quantity of the widescreen picture.

This means that an anamorphic widescreen picture is usually much superior to a standard one.

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Connections

So how do you connect your display of choice to your DVD player, Satellite receiver, etc? It probably will come as no shock to learn that there are a number of different methods. Please be aware that not all displays and other audio visual equipment have all of these connections. It 's usually the rule that the more expensive the device the better the connections available.

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RF Co-axial Cable

RF Co-axial Cable

This single cable is similar to an aerial lead and it carries both pictures and sound. This is usually provides the worst quality picture.



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Composite Video Cable

Composite Video Cable

This cable contains just the picture, although it is often accompanied by stereo audio out sockets. The cable is a standard phono cable (you can swap it with the audio connections). The picture quality is better than RF Co-axial but it is not the best.


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Scart

Scart

Only in Europe would such a cable be invented, and only in Europe is it used. These unwieldy huge connectors have the massive disadvantage that they are really easy to pull out and take up a fair amount of space. The cable carries both sound and audio signals.

Not only that but they carry both a composite video signal and an RGB signal. A composite video signal contains all of the video information mixed together, whereas a RGB signal splits the picture components (Red, Green and Blue) into separate signals. An RGB signal is therefore much more accurate than composite and leads to a better quality picture. The picture quality of Scart connections (especially the RGB Scart) is usually very good (with the RGB being possibly the best of all).

Note: Not all Scart cables have the RGB pins connected (the cheaper cables tend not to). Also note that not all televisions can accept RGB signals.

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SVHS

SVHS

These cables carry just the picture signal but it is an RGB signal. The quality of the picture is very good, if not excellent.

Where possible it displays should be connection by either SVHS or RGB Scart. The better quality the lead the better the picture. So shielded gold plated connections are not usually a waste of money.



Well thatís about it for displays.

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