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From: hull@hao.UUCP (Howard Hull)
Newsgroups: net.micro.amiga
Subject: Re: Technically speaking.. Flicker
Message-ID: <1924@hao.UUCP>
Date: Sat, 25-Jan-86 19:00:32 EST
Article-I.D.: hao.1924
Posted: Sat Jan 25 19:00:32 1986
Date-Received: Tue, 28-Jan-86 05:30:16 EST
References: <187@oberon.UUCP>
Distribution: net
Organization: High Altitude Obs./NCAR, Boulder CO
Lines: 36

If you know about television, then I presume you know that with interlaced
television, one field of 262 lines starts at the upper left of the screen,
whereas the other field (1/60 second later) starts at the upper center of
the screen and goes for half a line before continuing with full-length lines.
When the Amiga is in 320 or 640 by 200 mode, it simply lays the second field
directly on top of the first, all starting at the upper left.  Ordinary TV
usually blanks at least a 1.3 millisecond worth of lines (appx 20 lines per
field, or a total of 40 lines per frame) to black.  The Amiga blanks 62 lines
to black during vertical retrace (31 at the top, and 31 at the bottom) and
distorts the NTSC standard 3:4 vertical to horizontal aspect ratio by an
"adjustment" of the picture vertical height.  There is a distinct gap that
can be seen between the lines on the Amiga lo-res screen.

When the Amiga goes to 320 or 640 by 400 mode, it interlaces just like the
NTSC television standard does.  Now there is a barely perceptible darkening
between the lines, (their "Gaussian" profiles overlap somewhat) and there
is a distinct "jitter" in the general background.  The jitter is introduced
by the famous 1/30 second persistence problem.  On the television set, there
is as well the imprecision with which it manages to interlace the field line
positioning (or timing of each frame, depending on how you think of it).
As a general rule, you don't notice the flicker in television images because
the transmission bandwidth doesn't allow resolution of much better than 400
lines at the MTF limit (where a fine black and white checkerboard would be
rendered as gray); so features that would be on one line and would flicker
in the "clean" Amiga monitor are somewhat spread out and/or moving on the
television image.  I have the Amiga video modulator, and I notice far less
flicker in the interlace mode on the television set than on the Amiga 1080
monitor.  The resolution, color fidelity, purity, and stability on the 1080,
however, is VASTLY superior to what finally gets to the TV screen.  On the
TV, 80 column characters are just barely tolerable, and even so only close
up and for less than an hour - else even Meditating Guru Eyes will pop right
out of their sockets.
                                                                Howard Hull
[If yet unproven concepts are outlawed in the range of discussion...
                   ...Then only the deranged will discuss yet unproven concepts]
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