Clay wrote....
> > the same data for two frames. So lines (if you really look) are
actually
> > two TV lines tall.
>
> No, they're not. They're only one scanline tall, because the 2600 (and
> almost every pre-32-bit game system), puts out the same field continuously
I really don't want to get into a war of words with you. But hell, the rest
of my weeks been poorly so why stop now.
I still contend that on non-interlaced games, a '2600 'scanline' is actually
2 TV-lines tall. The first of those (or the second, take your pick) is
solid, and the other is blank. Therefore, it IS possible to split a '2600
scanline in half and double resolution.
Yes, emulators sometimes put in that extra blank line - in fact I suspect we
are agreeing but just saying it different ways. What the interlacing is
doing is shifting that second field down a scanline (on the TV, so that we
don't have that 'blank' line between scanlines anymore). We actually have
the odd lines, then even lines display - which is what interlacing is all
about. If we don't trigger the interlace by having that half-line timing at
the bottom of frame, then the TV doesn't do that shift, and we get the same
TV-lines written again for the second 'frame' - functionally idential to the
first.
And I contend that we ARE doubling the vertical resolution, as I originally
stated. We are achieving a '2600 playfield with 525 lines, instead of the
262 previously available. And scanlines ARE being split in half - their
vertical size (ie: the area on the TV picture each line covers) is being
reduced from 2 TV-lines to 1.
> It seems like you've misread the entire nature of this accomplishment. It
> causes the 2600 to generate an interlaced display, which is *not* the case
> normally.
Actually, I believe it was my posting a few months back ("Higher Resolution
through Interlacing" 29/June) which (re)started the ball rolling on
interlacing. I think you'll find that I described in that document pretty
much exactly what we are now seeing in Billy's proof-of-concept. I believe I
have a pretty good handle on how interlacing works, and why this demo works.
The main problem with that document is it fails to mention that we are
seeing line/blank in 'normal' '2600 non-interlaced displays. The principle
of the document is quite sound, though.
You wrote...
> Ummm. The usual 2600 scanline is equal to exactly one NTSC scanline.
There's
> no way you're going to cut that height in half without rewiring the TV.
> The test of interlaced output would be if a single scanline was TWICE AS
> THICK -- indicating that the 2600 was forcing output into both fields (as
> opposed to the same field, as per normal operation).
A scanline is a single frame's single line. That is, one line of a 262-line
1/60th second NTSC playfield/frame. So, a single '2600 scanline is actually
TWO NTSC scanlines (one blank) - another way of putting that, if we are in
interlaced mode, drawing the odd scanlines, then a single '2600 scanline is
line n and n+1. If you write the same frame twice, in interlaced mode, then
yes, that scanline will be twice as thick (visually) because we have shifted
the 2nd frame down by a line. But it's not a single scanline anymore, is
it. It is TWO! In short, two interlaced '2600 playfield lines = 2 TV lines
= 1 non-interlaced '2600 playfield line.
I really don't see why there's a problem with this. Aren't we describing
exactly the same thing?
To Erik's bruised ego...
> Just want to say that I called the correct way to do it almost two years
ago :)
I acknowledge your prior writings on interlacing - but was unaware of them.
Often things are thought of by different people independantly - but it's
those who actually do the experiment that deserve the adulation of the
crowd. It's actually our group as a whole that really deserves the
credit... Billy mostly for doing the experiment, but we have all contributed
in some way. I'm just happy to see new stuff happening on the machine after
all these years, and to have some small part to do with it.
Cheers
A
PS: Kudos to Billy and Glenn for their work on this.
PPS: Getting very keen on closed-captioning. Happy to collaborate with
anyone on this idea.
----- Original Message -----
From: "Clay Halliwell" <clay.h@xxxxxxxxxxxxxxxx>
To: <stella@xxxxxxxxxxx>
Sent: Tuesday, August 20, 2002 2:21 PM
Subject: Re: [stella] Interlacing Success!
> ----- Original Message -----
> From: "Andrew Davie" <adavie@xxxxxxxxxxxxx>
> To: <stella@xxxxxxxxxxx>
> Sent: Sunday, August 18, 2002 1:51 AM
> Subject: Re: [stella] Interlacing Success!
>
>
> > The '2600 programs to date have only been sending 262/312 lines to the
TV,
> > but - and here's the crucial bit - the TV has been effectively
displaying
> > the same data for two frames. So lines (if you really look) are
actually
> > two TV lines tall.
>
> No, they're not. They're only one scanline tall, because the 2600 (and
> almost every pre-32-bit game system), puts out the same field continuously
> (one frame is composed of two interlaced fields, remember?). Why do you
> think so many emulators have a "scan line" mode that blanks alternate
lines?
> The only classic system I'm aware of that generates an interlaced display
is
> the Bally Astrocade, and the difference is readily apparent.
>
> It seems like you've misread the entire nature of this accomplishment. It
> causes the 2600 to generate an interlaced display, which is *not* the case
> normally.
>
> Clay
>
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