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Before TV went digital, broadcasters had a big problem. When an analogue station transmitted a widescreen movie, it had to choose between cropping the sides or putting "letterbox" black borders at the top and bottom. Most viewers complained when they saw letterboxing, so TV set makers and some TV stations, most German networks and and Channel 4 in the UK, looked for ways to cater for film buffs who abhor cropping.
An analogue widescreen tv set could expand the letterbox image to fill its 16:9 screen. But there are only around 400 scanning lines in the letterbox. If they are "zoomed" to fill a 625 line screen, the picture looks coarse.
The MAC system was designed to solve this problem, with a signal that suited either type of screen. But MAC flopped.
In 1988 European electronics companies started five years work on PALplus.The black borders of the letterbox contain analogue "helper" signals. These let a PALplus tv set fill a wide screen with 625 line detail.
The European Commission backed PALplus to sell more of the widescreen tv sets developed for MAC. TV stations which transmitted PALplus programmes got a 50% subsidy.
In 1994 Britain's Channel 4 struck a nice deal with widescreen set-maker Nokia. The Finnish company paid the other half of C4's £1.5 million PALplus transmission bill. But so many viewers with ordinary sets complained about letterboxing that Channel 4 scrapped plans for PALplus horse racing. Some of C4's movies remained in PALplus though, for the benefit of the handful of viewers who bought sets. But there was no publicity.
By the mid 1990s it all became academic because digital TV was promised for 1997 far earlier than anyone had previously thought possible.