Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ncar!tank!uxc!uxc.cso.uiuc.edu!ux1.cso.uiuc.edu!phil
From: phil@ux1.cso.uiuc.edu
Newsgroups: comp.sys.amiga
Subject: Re: Warning: New User Question
Message-ID: <15500001@ux1.cso.uiuc.edu>
Date: 16 May 89 16:46:00 GMT
References: <1082@altos86.UUCP>
Lines: 32
Nf-ID: #R:altos86.UUCP:1082:ux1.cso.uiuc.edu:15500001:000:1805
Nf-From: ux1.cso.uiuc.edu!phil    May 16 11:46:00 1989


Flicker is an inherint characteristic of the fact that the real frame rate
of standard television is about 30 hz in (North and South) American and Japan
and is 25 hz in the rest of the world.  Interlacing scans only half the
lines the first time through, and the rest the next time.  So although the
sweep occurs 50 or 60 times a second, any ONE LINE is only updated half as
often.

The human eye notices the flicker if the brightness is different.  The rods
are sensitive to it, but the cones are much less so.  There are combinations
of colors that dramatically reduce flicker.  I use a yellow on blue color
combination that has relatively little flicker.  Because of the low contrast,
it is a little harder to read though.

Broadcast television does not suffer from flicker because the change from
one line (scanned in one cycle) to the next (scanned in the other cycle)
is very little.

Try the following with your Amiga.  Find a program (such as MicroEmacs) that
creates its own screen in interlace mode.  Now open this screen up overtop
a regular screen, and pull it down to the bottom.  The CRT scanning rate is
in interlaced mode, but the data on the regular screen is DUPLICATED for every
line pair.  You will see that there is much less flicker, but there is some
apparent JITTER.  This is what television is really like, but it also has
smooth gradations of intensity so even the jitter is not there.

High Definition Television, unfortunately, is continuing with the interlace
system at about the same frame rate.  Some TV sets do "super scanning" by
storing the picture in a frame buffer as received, and scanning EVERY line
out to the CRT at 60 hz or higher.  If you are lucky enough to have one of
these expensive units, you don't need a flicker fixer.  The prices will come
down some day.