Television standards conversion

Television standards conversion is the process of changing one type of TV system to another. The most common is from NTSC to PAL or the other way around. This is done so TV programs in one nation may be viewed in a nation with a different standard. The TV video is fed through a video standards converter that changes the video to a different video system.

Converting between a different numbers of pixels and different frame rates in video pictures is a complex technical problem. However, the international exchange of TV programming makes standards conversion necessary and in many cases mandatory. Vastly different TV systems emerged for political and technical reasons – and it is only luck that makes video programming from one nation compatible with another.

The first known case of TV systems conversion probably was in Europe a few years after World War II – mainly with the RTF (France) and the BBC (UK) trying to exchange their 441 line and 405 line programming.

The problem got worse with the introduction of PAL, SECAM (both 625 lines), and the French 819 line service.

Until the 1980s, standards conversion was so difficult that 24 frame/s 16 mm or 35 mm film was the preferred medium of programming interchange.

Perhaps the most technically challenging conversion to make is the PAL to NTSC.

The two TV standards are for all practical purposes, temporally and spatially incompatible with each other.

Aside from the line count being different, it is easy to see that generating 60 fields every second from a format that has only 50 fields might pose some interesting problems.

Every second, an additional 10 fields must be generated seemingly from nothing. The converter has to create new frames (from the existing input) in real time.

TV contains many hidden signals. One signal type that is not transferred, except on some very expensive converters, is the closed captioning signal.

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