Re: Converting NTSC to PAL and vice versa

In article <gq8dmc$247$1@xxxxxxxxxxxxxxxxx>, billy@xxxxxxx wrote:

isw <isw@xxxxxxxxxxx> writes:

You're right; the NTSC field rate is 59.94..., and the frame rate is
precisely half that, 29.97... For compliance with the NTSC spec, those
rates must be correct =/- a few parts per million, although most TV sets
can handle a bit more deviation than that
[...]
For best performance, the color subcarrier, the horizontal rate, and the
vertical rate, are all locked together in a very specific way

Back in the good old days of monochrome (black and white) television the
field rate was conveniently the same as the American AC mains - 60Hz.

Then, when NTSC color arrived, and was broadcast over the air, there were
problems with the sync signals and subcarriers interfering with each other,
so the frame rate (which affects everything else, as mentioned above) was
adjusted to to fix this. See, for example, the Color Encoding section of
http://en.wikipedia.org/wiki/NTSC for a detailed explanation.

But - this is only a problem in analog transmission. NTSC works fine at
60Hz otherwise...

It sort-of works, but the image quality is not what it could be, because
the color subcarrier is not properly synchronized with the horizontal
and vertical rates. In "proper" NTSC, the color information is
interlaced too; not just the H and V. Raising the color subcarrier by
one part in a thousand (the difference between 59.94 and 60) to regain
interlace won't work because the color circuitry in receivers can't
adjust that far.

Most VCRs (in the US) record at 59.94 FPS and play back at 60 FPS. Also,
most "TV" outputs on computer video cards do not properly interlace the
color signal.

Isaac
.

Relevant Pages

  • Re: Converting NTSC to PAL and vice versa
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