[Richard Fry]

Don Pearce wrote:
Look, it doesn't matter if the black is at the top or the bottom
of the signal, it will have exactly the same amount of noise on it.
Likewise the white.

Consider... when black is being transmitted, the r-f power radiated by
a TV station is greater than when white is being transmitted.
Therefore the field strength produced at a receiving antenna is higher
for black than white, and a given value of r-f noise will be a lesser
percentage of the received signal during transmission of black then
white. In other words, black (and sync, which is blacker than black)
will have a higher signal-to-noise ratio.

However noise voltage tends to drive the detected video waveform about
as far in negative polarity as it does positive. Therefore the
average change in light output from the display (CRT, etc) across a
complete cycle of noise energy can be close to zero, at a normal
viewing distance.

This effect is lost, though, for noise on low luminance video, because
the negative-going noise pulses can extend below reference black where
the display cannot fully show them, whereas the opposite noise
polarity will be fully shown at that luminance level.

RF