Xref: utzoo comp.graphics:6992 rec.video:7576
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cornell!uw-beaver!ubc-cs!alberta!calgary!ctycal!ingoldsb
From: ingoldsb@ctycal.COM (Terry Ingoldsby)
Newsgroups: comp.graphics,rec.video
Subject: Re: HDTV and ATV Glossary (TN32)
Message-ID: <438@ctycal.UUCP>
Date: 18 Aug 89 23:30:46 GMT
References: <120919@sun.Eng.Sun.COM> <121076@sun.Eng.Sun.COM> <428@ctycal.UUCP> <12045@ulysses.homer.nj.att.com>
Organization: The City of Calgary, Ab
Lines: 39
Keywords: 525/59.94, 625/50, NTSC, PAL, SECAM, Component, Composite,
Summary: Interlace *usually* works

In article <12045@ulysses.homer.nj.att.com>, ggs@ulysses.homer.nj.att.com (Griff Smith) writes:
> In article <428@ctycal.UUCP>, ingoldsb@ctycal.COM (Terry Ingoldsby) writes:
> > In article <12027@ulysses.homer.nj.att.com>, ggs@ulysses.homer.nj.att.com (Griff Smith) writes:
> > > ...  What is so evil about interlace?
> > > 
> > Interlace can be a real pain if you want to draw thin horizontal lines, or
> > diagonal lines that cause only a single pixel to be illuminated on a scan
> > line.  In these cases the refresh rate is only the frame rate (eg. 30 Hz),
> > not the field rate, and flicker becomes quite annoying.  You can
> > occasionally see this on poorly designed text overlaid during TV sports
> > programs.  The flicker can be very visible.
...
> I don't think I've ever noticed this.  If this is the kind of argument

The TV people are very careful to avoid this situation, so you won't see
it very often.  Once in a while they screw up and it is visible.
...
> 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?

Interlace IS a good way to cut the bandwidth in half and still give relatively
good performance wrt flicker, etc..  It is not a *perfect* solution.
Interlace is not bad for low resolution images (ie, almost everything spans
two horizontal lines).  High res images, or those created by a computer can
be a pain with interlace.

These problems can be overcome at the receiver by taking the interlaced
info, storing it in a frame buffer, and clocking in out (non-interlaced)
at 60 frames per second.  Even though the odd/even info is only changing
every 1/30 of a second, it is refreshed more often and so it doesn't
flicker.  Motion artifacts might still be visible.  Note that this is
roughly equivalent to a CRT with a 1/30 sec persistence on the phosphor.

-- 
  Terry Ingoldsby                       ctycal!ingoldsb@calgary.UUCP
  Land Information Systems                           or
  The City of Calgary         ...{alberta,ubc-cs,utai}!calgary!ctycal!ingoldsb