Thursday, March 09, 2006

Tech Musings - NTSC is not your PAL

Spend any time with video and you'll come across the four-letters "NTSC." Contrary to some beliefs, it is not an acronym for 'Never Twice the Same Color'.

From its early days, American television has 525 lines of information that is refreshed 30 times each second. NTSC color was designed so that it would not obsolete the thousands/millions of existing black-and-white television sets of the era (the 1950s).

If you are a real glutton for punishment, dig out some NTSC reference books and spend a month or three with information theory math. In just a brief dozen weeks or so, you too can learn about the complicated interaction between scanning lines, refresh rate, fields versus frames, signal bandwidth, luminance resolution, and other exciting stuff.

You'll learn how the color subcarrier was chosen to "fit in between" the parts of the bandwidth that are not used by the luminance signal; specifically, so that it would NOT affect the resolution. And why, until the digital era, that choice made recording a television signal so difficult. (The only change that occurred for the b/w set owners of the time was a slight adjustment of their horizontal hold control to compensate for the change from 60 fields/sec to 59.96...fields/sec.)

NTSC --> Natonal Television Systems Committee, a group that meets to develop standards for television.

Tomorrow - "Why French television is more of a PAL."

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