Xref: utzoo comp.graphics:6969 rec.video:7561
Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.csd.uwm.edu!bionet!ames!vsi1!daver!apt!brian
From: brian@apt.UUCP (Brian Litzinger)
Newsgroups: comp.graphics,rec.video
Subject: Re: HDTV and ATV Glossary (TN32)
Keywords: 525/59.94, 625/50, NTSC, PAL, SECAM, Component, Composite,
Message-ID: <1674@apt.UUCP>
Date: 18 Aug 89 07:30:25 GMT
References: <120919@sun.Eng.Sun.COM> <121076@sun.Eng.Sun.COM> <428@ctycal.UUCP> <12045@ulysses.homer.nj.att.com>
Followup-To: comp.graphics
Organization: APT Technology, Inc., San Jose, CA
Lines: 61

From article <12045@ulysses.homer.nj.att.com>, by ggs@ulysses.homer.nj.att.com (Griff Smith):
> 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:
>> > I assume this is part of the attempt to get rid of interlace so the
>> > computer graphics folks can avoid motion artifacts.
>> > ...  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
> that is being used, I think the industry is putting something over on
> us.

I've noticed interlaced video flicker quite abit. I've been involved in
high resolution graphics (>1024x1024) since 1983.  Flicker from interlaced
video comes from two major causes.

One, horizontal lines or diagonal lines with long segments that are
horizontal tend to flicker because they are refreshed at have the
effective rate of the overall screen.  Blue usually flickers the most
followed by red, then green.

Two, the interfield registration of the two interlaced fields.  Some
people call this jitter.

Your ability to sense flicker is also affected by several things.

One, the persistence of the phosphers used in the display.  Long
persistence displays reduce flicker problems, but are generally
dimmer and lower your effective resolution because of the slower
response of the phospher.

Two, some companies, such as IBM, substitute a phospher which
produces a color called 'sky blue' rather than 'blue' in their
normal persistence monitors.  This reduces flicker problems in the
most  "flickery" color.

Three, the age of your eyeballs.  Older eyeballs often have a harder
time detecting flicker on displays.  Similar to how older ears can
have difficulty detecting higher frequency sounds.

Four, knowing what flicker looks like.  Often times people never
notice the flicker because no one ever pointed it out.  Similar to people
who have never noticed the panning that goes on in movies that have
been transfered to television.

> Interlace seems to be an excellent way to cut the bandwidth in half
> while avoiding flicker and motion artifacts.

There ain't no such thing as a free lunch.  You definitely give up
something with interlaced video.  Have you seen the TOSHIBA double
scanning television?

<>  Brian Litzinger @ APT Technology Inc., San Jose, CA
<>  UUCP:  {apple,sun,pyramid}!daver!apt!brian    brian@apt.UUCP
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