On Thu, 19 Oct 2000 10:07:16 GMT, grcook@my-deja.com wrote:

>Got a Q about video wipes ... while dragging a vertical
>line across the screen in a drawing package I noticed that
>if you drag it really quick, you get the effect that you
>can see more than one vertical line ... got me thinking
>as while watching sky sports (in the UK) they use wipes
>all the time ... and the vertical bars never show this
>effect ... it's really smooth ... now, I imagine that they
>don't allow the position of the bar to change during active
>picture ('cos then you'll see a step) then they have to do
>it on a field or frame boundary ... say they do a wipe
>across the screen in 1s, and using pal that's 50 frames
>per second, that gives them 50 points during the wipe where
>they can change the bar position. Which I assume should be
>enough for it to appear smooth ...
>
>so...if I drag my vertical line across my screen in 1s, I see
>at least a double line effect ... why? Is this something to
>do with interlace? If so, how do Sky do such nice wipes????

Interlaced video seen on a non-interlaced computer monitor
will show problems with motion, just as non-interlaced
("progressive-scan") video shown on a TV will show
problems with motion - using the appropriate viewing
system for the video type will give the sharpest image
with motion...