RE: re Digital TV !!!OFF TOPIC!!!

[Mike Griffiths <mike@xxxxxxx>]

-----Original Message-----
From: Phil Harris [mailto:phillip.harris1@xxxxxxx]
Sent: Sat 19 Jan 02 12:18
To: ukha_d@xxxxxxx
Subject: RE: [ukha_d] re Digital TV !!!OFF TOPIC!!!


> For the record
> The interlace system was devised to stop flicker
> On early TV sets using a non interlaced TX systm produced
> unacceptable flicker

My understanding of this is that it was known that to stop the image
flickering too badly then the image would have to be redrawn at 50 times
a second, however the bandwidth (and the technology) available at the
time was insufficient to allow a full 625 line (which was the then
equivalent of HiDef after the previous 405 line standard) image to be
redrawn 50 times a second which is why they had to have two interlaced
fields and a longer persistence phosphor on the TV tubes.

Interlacing in itself does not reduce or stop flicker however in
situations where the available bandwidth is limiting the ability to
transmit full frames at a high enough frame rate then interlacing the
image (in effect havling the data rate) is a possible compromise as it
fools the eye.

As for current HiDef broadcasts - I understand that there are both
progressive scan *AND* interlaced standard for the various HiDef
resolutions which should "sort" the problem in the same way that
the
problem is sorted already - i.e. BADLY! I haven't however had any
reports back from a couple of techie mates in the US that they've seen
flicker on their HiDef stuff out there - of course I can't say one way
or the other since we don't get any HiDef stuff here other than the
1,024 line progressive stuff that drops out of the arse end of my video
scaler! (And of course that's only from a 525 or 625 line interlaced
source anyway so hardy the same.)

Phil



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