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From: keithd@cadovax.UUCP (Keith Doyle)
Newsgroups: net.micro.amiga
Subject: Re: Technically speaking.. Flicker
Message-ID: <1000@cadovax.UUCP>
Date: Thu, 23-Jan-86 18:24:25 EST
Article-I.D.: cadovax.1000
Posted: Thu Jan 23 18:24:25 1986
Date-Received: Sun, 26-Jan-86 04:25:07 EST
References: <187@oberon.UUCP>
Reply-To: keithd@cadovax.UUCP (Keith Doyle)
Distribution: net
Organization: CONTEL CADO Systems, Torrance, CA
Lines: 65

In article <187@oberon.UUCP> spencer@oberon.UUCP (Randy Spencer) writes:
>I really need a good description of exactly why is it that the Amiga will
>flicker in the 400 mode.   ......... 

>.......       If the IBM pc only has 200 lines why is it that there is
>not such a noticeable dark line on the undrawn line, how about the C64?

Jeez, I always thought the black lines between the lines on the IBM PC 
to be VERY noticeable.  A color filled rectangle on the screen to me 
looks like it was filled with a horizontal stripe pattern.  But, I have
been using better than average monitors, I`ve noticed the standard PC
monitors have such a large dot-pitch that the color dots just seem to
smudge the video all together, somewhat covering up this black-line
problem.

>I had always assumed that it was just repeating the lines to fill up
>400 lines worth of space.

Wrong.  The lines are interlaced so the apparent overall screen flicker
is at 60hz not at 30hz.  Actually, though, real small details ARE flickering
at 30hz, not 60hz, if they are smaller than 2 lines high.

>Perhaps the real problem that I could not figure out in my own head is,
>if the Amiga had to flicker to remain compatible with NTSC, why is it
>that even the highest resolution video of the day will not flicker like
>the Amiga?  Infact, no one ever mentioned that NTSC flickered to me before,

This is because most video programs are made up of signals that do not have
a lot of horizontal hard edges and/or lots of small detail with lots of
contrast.  By the same token, depending on what you are displaying on the
Amiga screen, you may or may not notice the flicker.  In using Deluxe-Paint
in hi-res mode the menu bars and stuff flicker like a SOB, but I've painted
several pictures that use a lot of grey-scale and don`t have a lot of
horizontal edges that don't flicker any more than the lower res pictures.
It all depends on what you are displaying.  Computers tend to be worst
case, character displays have a lot of small details, and other computer
pictures can be inclined to have a lot of skinny horizontal lines.  Video
images don't have this problem much, except sometimes you might notice such
flicker on nightly news/weather programs where they are using some kind of
display generator, or color keying or something that produces a contrasty
horizontal edge.

>Any chance it has to do with unstable sync signals from the Amiga, when
>I run Setlace it sure seems to start shaking the formerly rock steady
>lines around on the screen.
>
>Randal Spencer      Student DEC Consulting - University of Southern California

Again, when you run setlace, the horizontal edges flicker at 30hz, instead of
60hz.  Depending on what you are displaying, (and window boxes like to present
plenty of horizontal edges) this problem is noticable to a varying degree.
Adjusting the preferences colors can minimize this effect somewhat.  Using
all pastel type colors, for both background and foreground usually helps.

I expect the up and coming camera digitizer add-on should provide a ready
means to input video-like images to the hi-res mode that should prove to
have little flicker, just like the usual video images we are all used to.
Can't wait for this little bugger to become available, though they better
save the pictures in EA's IFF format so I can use Deluxe Paint to monkey
with them.

Keith Doyle
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