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FEATURE

 

HOW TO… TV SYSTEMS & STANDARDS

 

PAL

Phase Alternate Line – 625-line/50Hz colour TV system developed in Germany in the mid 1950s, first regular broadcasts began in the UK in 1967, adopted throughout much of Europe, the Middle East, Australia and New Zealand. PAL good for sharp picture and superior colour accuracy, but 50Hz frame rate can cause noticeable picture 'flicker' on larger screens.

 

NTSC 3.38

National Television Standards Committee – world's first colour TV system transmissions started in 1954; sometimes called Never Twice The Same Colour due to slightly wobbly colour characteristics. Based on

525-line/60Hz picture, also used in South America, Japan and much of the Asia. 3.38 is the frequency (in megahertz) of colour sub-carrier signal); NTSC 4.43 is a system variant used for video recording.

 

SECAM

Sequential Couleur a'Memoire – 625-line/50Hz colour TV system developed in France (allegedly it's just sufficiently different from PAL to avoid infringing patents…). MESECAM variant adopted by the former Soviet Union and Eastern European countries. Performance very similar to PAL and SECAM video signals can be displayed on PAL TVs, in black and white.

 

PAL-M/PAL-N

PAL-M is a hybrid system using NTSC brightness information and PAL colour processing, only used in Brazil. PAL-N is a narrow-bandwidth system variant, currently only used in Argentina, Paraguay, and Uruguay

 

D-MAC/MAC

Multiplexed Analogue Component – hybrid analogue/digital system used for satellite broadcasting, where picture (brightness) and colour information are transmitted separately, primarily to reduce the impact of atmospheric interference on the signal.

 

HI-VISION

Hybrid analogue/digital high definition satellite TV system, only used in Japan. 1125-line picture with 60 and 100Hz frame rates, 16:9 widescreen picture format

 

PAL 60/PSEUDO PAL

Strictly speaking not a CTV standard but a recording system used on VCRs and DVD players that partially converts NTSC video signals so that they can be displayed on recent PAL TVs.

 

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STRAP

HOW TO… CHOOSE THE RIGHT TYPE OF TV/PROJECTOR

 

DIRECT VIEW CRT

The granddaddy of all visual display technologies – the cathode ray tube was first developed in 1895 -- and it is still the best and most cost-effective option for most applications. CRTs give the brightest and sharpest picture under the widest range of viewing and lighting conditions however maximum screen sizes are limited to around 38 inches due to the weight and fragility of picture tubes. Life expectancy is around 5 to 8 years before there's a noticeable drop in performance.

 

DIRECT VIEW LCD

Liquid Crystal Displays are the new kids on the block; in fact LCD panels have been around for years on PCs but now they're getting big enough for serious TV viewing.  Plus points are the flat hang-on-the wall construction and long life expectancy, the down side is price, shallow viewing angle, relative – compared with CRT -- lack of brightness and contrast range and it's unlikely they'll ever get much bigger than 32-inches across due to difficult of manufacture.

 

PLASMA

Clever mixture of old CRT and modern flat panel digital display technologies, with close to CRT performance in terms of picture sharpness and colour accuracy. Brightness and contrast are improving all the time but are still some way behind CRT; viewing angles are also a little shallower. Plasma screens tend to be large 40-inches plus, due to economics of manufacture and (currently) highish reject rate so they can be very heavy, and they are all very expensive.

 

REAR PROJECTORS

Basically a big box containing a video projector shining onto the rear of a large translucent screen via a set of mirrors, which makes them relatively compact, as far as depth is concerned. Screen sizes take over where CRT leaves off -- between 40 and 65-inches -- picture performance varies according to the projector technology (see CRT, LCD & DLP projectors). Screen brightness also varies but generally back projectors are best suited to low to moderately bright lighting conditions.

 

CRT PROJECTORS

Ideal for medium to large screen sizes from 80 to 200 inches and they perform best in near-dark lighting conditions. The image is generated by three high intensity picture tubes – red green and blue – giving arguably the best image quality (highest resolution, widest contrast range and most accurate colours), but picture line structure can be noticeable, they can take longer to set up, the tubes have a relatively limited life and can be expensive to replace.

 

LCD PROJECTORS

Screen sizes of 500 inches and more are possible however most domestic models are in the 100 to 300-inch range. A single light source shines through three small LCD elements, one for each colour component (red, green & blue), so there's little to wear out, apart from the lamp (and they can be very expensive…). Picture quality not as good as CRT, pixellation is usually evident, they can also have a narrower contrast range and inferior colour fidelity but they tend to be cheaper and performance is improving all the time.

 

DLP PROJECTOR

Digital Light Processors or 'micromirror' devices are the next big thing in video projectors. They're based on chips covered with thousands of thousands of microscopic mirrors, they're very efficient and the projectors can be small but capable of throwing up large bright images in the range 100 to 500 inches, even in difficult lighting conditions. Picture quality can be excellent, often described as 'film like' due to lack of pixellation and line structure, good contrast range and colour accuracy and prices are coming down quickly.

 

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Ó R. Maybury 2001, 0902

 

 

 

 

 

 

 

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