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It is possible to regenerate colour from a NTSC or PAL signal that lacks its colour burst. It was called chromalock and was not reliable. Worse in PAL because it has no information aboujt the polarity of the PAL Switch which had to be set manually.
Why do this at all? Because sometimes the burst would be removed to prevent colour being received. I forget why this was sometimes done.
NTSC and Timecode. AAAARRRRGGGHHH!!! I'm looking at the old NTSC papers in the IRE journal from 1954 which explain the reasons. The H and V frequencies were reduced by 0.1% to minimise patterning that could arise between the sound carrier and colour subcarrier. This avoided retuning the sound circuits on monochrome sets. It seemed harmless at the time. Some years later timecode was invented. The lack of a sensible relationship between frame rate and time of day has caused massive amounts of hassle.
The relationship between subcarrier and H had to be fixed (at an odd multiple of H/2) to minimise visibility of subcarrier on monochrome sets.
PAL is more complex (quarter line offset + half frame offset) which doesn't have a problem against the sound carrier. Hence we have no timecode problems in 50Hz countries.
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