28 May
2010
28 May
'10
12:55 p.m.
On 27 May 2010 at 19:24, Tony Duell wrote:
At least on NTSC, the half-line setup works like this. Scan lines on
Ame on every oth TV standard I've looekd at.
Ok.
thanks for the info. Just one more question; why only an odd
number of lines?
For resons of getting the best piture from the available bandwidth,
all analouge broadcast TV systems use interlaced scanning. And that
pretty much requires a 'half line' in every field, so a total of an
odd number of lines. a TV CRT are not horizontal--they slope slightly down
as they are
scanned from right to left. So, the second field begins with the
Yes, the vertical deflection is a continuous ramp, not a staircase. So
the right hand end of the line is lower (it occurs later in time, so the
vertical signal has mobed down a bit) than the left end.
beginning of the vertical sweep, but offset from the
left of the
screen by exactly one-half line. The net result is that the lines on
the second field of a frame fall exactly between the lines of the
first field.
Yep...
The vertical synchronizing in the US system is quite clever,
consisting of varying (depending on odd or even fields) numbers of
pre-equalizing pulses (at twice the horizontal frequency) before the
vertical sync pulse train and a similarly variable number of post-
equalizing pulses following.
That's ow it's done in the UK 625 line standard (and I would guess the
others too).
-tony