Technology: Wide screens split BBC and Channel 4ry Fox (original) (raw)

Viewers who want to watch future widescreen television broadcasts by
the BBC and commercial stations will have to buy two different widescreen
reception systems. A deep-rooted policy difference between the two networks
means that they will be using incompatible transmission systems.

From October, Channel 4 will begin transmitting some programmes in widescreen
format, with pictures that have a width-to-height ratio of 16:9 instead
of the 4:analogue system called PALplus, which builds on the existing PAL
TV system used in Europe and Australia. Granada TV says it will also broadcast
some widescreen programmes before the end of the year.

A conventional PAL TV picture is built up from 625 horizontal scanning
lines, of which 576 are ‘active’ lines that trace the picture on the screen.
The other 49 lines are largely lost off the top and bottom of the screen.

In PALplus transmissions, only 432 of the lines are active, but on a
PALplus TV set with a widescreen picture tube they will fill the screen.
The resolution lost through using fewer line is restored by using a ‘helper’
signal encoded in the 144 extra spare line. This signal conveys fine detail,
and viewers see pictures that are clearer as well as wider than normal.

Viewers with existing PAL TV sets will see the same programmes, but
in ‘letterbox’ format. The 144 extra spare lines will form thick black bars
that will be clearly visible at the top and bottom of the screen.

Unlike the commercial networks, the BBC plans to transmits its widescreen
programmes using a digital technology, which is not yet ready. Its digital
widescreen transmissions will be entirely separate from the analogue BBC1
and BBC2 channels, and will use spare frequencies slotted between
them. The government recently cleared the way for this in its White Paper
The Future of the BBC.

The BBC’s widescreen programmes will be wholly incompatible with all
existing sets. Viewers who want to receive them will have to buy a widescreen
TV set with a digital decoder. Everyone else will continue to watch BBC1
and BBC2 as normal on their existing PAL sets.

Widescreen TV will bring two benefits, according to broadcasters. First,
they can show feature films in the proportions that their directors intended;
on 4:3 screens, either some of the side of the picture must cropped out,
or it appears in a letterbox, with black bands above and below. Secondly,
the panoramic screen is regarded as a more natural viewing format than the
present, boxy form.

PALplus was developed by a consortium of European electronics companies
and broadcasters, with help from the BBC. However, Mick Gleave, the corporation’s
engineering adviser on standards policy and planning, says it has ‘no plans
to introduce PALplus’. The BBC’s engineers are already planning for a digital
future, and see PALplus as a costly diversion.

The electronics company Nokia will have widescreen TV sets with built-in
PALplus decoders ready for sale in October, priced at POunds Sterling 1300.