Television Standards

1. Television Standards
Charmaine Harris

2. What is it?
• Television standards conversion is the process of changing a type of
television system to another.
• The most common switch is from NTSC to PAL, or vice versa. This is
because TV shows that are seen in one nation may be viewed in another
nation in a different standard.

3. A Little History
• The first known case of TV conversion was in Europe a few years after
World War 2.
• It was mainly between two channels: RTF (France) and the BBC (UK).
• Until the 1980s, conversion was so difficult that 24 frames per second was
the preferred medium of programming.

4. PAL to NTSC
• The most technically challenging conversion that is made is the PAL to
NTSC.
• PAL is 625 lines at 50 fields per second, and NTSC is 525 lines at 59.94 fields
per second.
• Every second an addition 10 fields have to be produced for basically nothing.
This means that the converter has to create new frames (from the existing
input) in real time.

5. Hidden Signals
• Television has many different hidden signals. One type of signal that doesn’t
get transferred (however it does on some expensive converters) is the closed
captioning signal.
• Teletext signals don’t need to be transferred, however if it is technically
possible to do so the captioning data stream should be transferred.

6. Theory Behind Systems Conversion
• Information theory and the Nyquist-Shannon sampling theorem suggest that the
conversion from on TV standard to another will be easier if;
• It’s going from a higher frame rate to a lower frame rate (NTSC to PAL).
• It’s going from a higher resolution to a lower resolution (HDTV to NTSC).
• It’s converting one progressive source to another progressive source.
• Interframe motion is limited.
• Signal to noise ratios in the source material are not detrimentally high.
• The source material does not possess any continuous (or periodic) signal defect that
inhibits translation.