HOW TO… TV
SYSTEMS & STANDARDS
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.
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
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.
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 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
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
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
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.
HOW TO… CHOOSE
THE RIGHT TYPE OF TV/PROJECTOR
DIRECT VIEW CRT
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
DIRECT VIEW LCD
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.
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.
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
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.
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.
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.
Ó R. Maybury 2001, 0902