by jss

What's the story with NTSC, PAL, SECAM?

a few friends of mine have been asking about this, so i decided to do some research.

there are three video formats used in the world. each one is incompatible with the others: PAL, NTSC, SECAM

america and canada use NTSC, which stands for National television system committee. this was the first colour tv broadcast system. NTSC is also used in Asia, including Japan. western europe and australia use PAL, or phase alternating line format. PAL was developed in the early 1960's.. the increased bandwidth allows for better picture quality. eastern europe and france use SECAM, or sequential couleur avec memoire (sequential color with memory). SECAM uses the same bandwidth as PAL but transmits the colour information sequentially.

the differences exist because of field timing reference signals. these signals tell the TV or receiver to be ready to receive the next picture in a stream of images. TV equipment used the frequency of the AC current as source for this timing because it was easy and readily available (obviously). if the equipment and televisions weren't exactly in sync, you would see large rolling bars on TV monitors on video and cause massive flicker. since AC currently in the world is wither 50Hz or 60Hz, this caused two groups of video formats.. 25 frames/sec (50Hz) and 30 frames/sec (60Hz). Later when colour was added, 60Hz formats changed to 59.94Hz. The addition of colour actually messed things up even more, which is what PAL was to solve. NTSC was soon dubbed, Never The Same Colour. PAl was supposed to correct shifts in the colour sub-carrier phase of the signal. Every other line has its phase in reverse order, which is why it's called Phase Alternate Lines. People joked that it stood for Pay for Added Luxury (re: cost of delay line). France fixed the colour problem on their own with SECAM, which people said stood for System Essentially Contrary to American Method. Eastern Block countries adopted this format for purposeful incompatibility with western transmissions, possibly also political reasons.

type    lines   horizontal freq vertical freq
------  ------- --------------- ---------------------
NTSC    525/60  15.734kHz       60Hz
PAL     625/50  15.625kHz       50Hz
PAL-N   625/50  15.625kHz       50Hz
PAL-M   525/60  15.750kHz       60Hz
SECAM   625/50  15.625kHz       50Hz

and that's why there are multiple formats, where they are supported, and what they mean.


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