gnupic@linuxhacker.org

On Fri, Mar 14, 2003 at 06:28:36PM +0100, Ralf Forsberg wrote:
> On Fri, Mar 14, 2003 at 12:59:01PM -0400, Daniel Serpell wrote:
> > 
> > Count the number of equalization pulses (eq. pulses are at
> > twice the H freq) after VB.
> > ->Even number of pulses -> even frame
> > ->Odd number of pulses -> odd frame.
> 
> I do almost exactly that now, only I compare the number of pulses with
> the number in the last frameand guess that the one with more pulses
> is 'first' frame. Is that the same thing, or would it be better to
> compare odd/even?
> 

Yes, should work in "correct" TV signals, because the number of
equalization pulses should be the same in all even or odd frames. The
difference will be in "bad interlaced" signals: if the difference in
pulses is betwen frames is even, a TV set will display the two fields
in the same possition, in fact the number of eq. pulses set's the
vertical position in the frame (each eq. pulse ammounts to half a line,
that's why you show even/odd fielfs interlaced).

Some TV output circuits (like the one in my old Atari 800) output
non-interlaced signals, in this case the two fields have the same number
of eq. pulses.

    Daniel.