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FLAT-SCREEN television with cinema quality came closer to reality last
week when Japan’s state broadcasting authority, NHK, displayed a colour
plasma screen 80 centimetres across. It is the latest technological advance
in NHK’s effort to make its ‘Hi-Vision’ system of high-definition television
(HDTV) acceptable to the public.

No manufacturers in Japan have yet put Hi-Vision receivers on sale,
because the cost is so high. NHK is convinced that HDTV will take off only
when flat screens are widely available. ‘Our polls show that people think
the best effect is in screens larger than 127 centimetres,’ said Yoshiro
Nakamura, NHK’s engineering director, ‘but to have a cathode-ray tube (of
this size) in Japanese rabbit-hutch homes is unrealistic. To penetrate the
mass market, we have to create flat-panel displays.’

Several companies already make large monochrome plasma screens, but
producing them in colour with reasonable definition is proving more difficult.
The plasma screen NHK displayed last week has an array of 800,000 cells.
Each one, when activated in a way similar to fluorescent lights, excites
a phosphor screen into emitting the primary colours red, green and blue.

The screen still has several drawbacks. The prototype is only as large
as a conventional television screen and is not yet as bright as a cathode-ray
tube.

Last week, NHK claimed another world first in the broadcast technology
it believes will succeed HDTV – 3-D colour. Engineers demonstrated a prototype
colour screen 96 centimetres across which shows 3-D images that can be seen
without having to wear special spectacles. They claimed it is the world’s
largest such system.

The screen works on a principle more familiar on ‘3-D’ postcards: a
grille of semicircular lenses separates images projected from the display
so that the left and right eyes see slightly different views. A viewer sitting
still in exactly the right place sees 3-D colour.