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From: ggs@ulysses.homer.nj.att.com (Griff Smith)
Newsgroups: comp.graphics,rec.video
Subject: Re: HDTV and ATV Glossary (TN32) (really interlace)
Summary: I think I've heard this story before
Keywords: 525/59.94, 625/50, NTSC, PAL, SECAM, Component, Composite,
Message-ID: <12052@ulysses.homer.nj.att.com>
Date: 18 Aug 89 13:38:02 GMT
References: <120919@sun.Eng.Sun.COM> <121076@sun.Eng.Sun.COM> <428@ctycal.UUCP> <1612@unccvax.UUCP>
Organization: AT&T Bell Laboratories, Murray Hill
Lines: 39

In article <1612@unccvax.UUCP>, dya@unccvax.UUCP (York David Anthony @ WKTD, Wilmington, NC) writes:
> In article <12045@ulysses.homer.nj.att.com>, ggs@ulysses.homer.nj.att.com (Griff Smith) writes:
> 
> > Interlace seems to be an excellent way to cut the bandwidth in half
> > while avoiding flicker and motion artifacts.  Other than pressure
> > from the movie industry, what are the other arguments for eliminating
> > interlace?
[deleted some good arguments against interlace]
> 	Yes, interlacing does save approximately half the bandwidth,
> but it also cuts the information content in the diagonal and vertical
> domain.
> 
> York David Anthony
> BPH-880505OT (WRPL) Wadesboro, NC

Thanks, I think I learned something.  This all seems familiar, though.
Back in the 1970's, people in the computer industry were moaning about
the evils of using NRZI encoding for magnetic data tapes: poor clock
recovery, no skew correction, etc.  The solution was (flourish of
trumpets) Phase Encoding.  Double the bit density, but reserve half the
bits for flux change references.  We all thought this was wonderful.
But the next revolution went back to NRZI.  In the interim, the
advances in electronics had made it possible to conquer the NRZI dragon.
They used GCR to make the flux change density high enough to ensure
proper clock recovery.

I would be delighted to see 60 hz progressive scan HDTV, but I assume
we can't afford the bandwidth yet.  Given a choice between using 30 Hz
progressive scan with motion artifacts caused by frame doubling, and
using 60Hz interlaced scan with alternate fields digitally synthesized
to eliminate twitter, I'll take the latter.  I think a lot of the
problems you describe will go away as more intelligent receiving
equipment becomes available.  24 Hz is a short-sighted standard, and
I'm annoyed that it's even being considered.
-- 
Griff Smith	AT&T (Bell Laboratories), Murray Hill
Phone:		1-201-582-7736
UUCP:		{most AT&T sites}!ulysses!ggs
Internet:	ggs@ulysses.att.com