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nikoniko
Account closed
Registered: Dec 2006
Posts: 1 |
New video modes? 320x400 and 160x400
Hi all,
Hydrophilic/Hydradix over at the Commodore 128 Alive! forums has been working on a technique to achieve 320x400 and 160x400 interlaced modes on a C128, taking advantage of the VIC IIe's undocumented test bit to allow fine control of raster output. He's succeeded in getting it to work for NTSC (at least on his own TV), and has now put up a simple demonstration and instructions on fiddling with the settings. Anyway, with some experimentation it sounds like it could turn into something pretty cool, especially if some bright minds here could combine it with other techniques.
I know this place is mainly about 64 coding, but since the approach should also work on 128s in 64 mode, I thought you might like to know about it.
Here's his announcement: http://landover.no-ip.com/128/viewtopic.php?pid=2637
And here's his webpage, which goes into some detail about the technique: http://www.geocities.com/hydradix/C128/Interlace.htm
And finally, here's the original forum discussion while he was working on it: http://landover.no-ip.com/128/viewtopic.php?id=807
I believe he's tried to make it easy to tweak, so PAL support could probably be achieved by someone who wants to play with it.
I'd recommend that if you want to ask him questions, the forums I linked to are probably the best place since he's a frequent poster over there.
Cheers,
nikoniko |
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Oswald
Registered: Apr 2002
Posts: 5028 |
still a real interlaced display uses the half lines, independant of the scrolling speed. |
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Copyfault
Registered: Dec 2001
Posts: 467 |
Now I at least think I got the point Mager Valp&radiantx tried to make clear: the image we get when scrolling up by 1 pixel every 2nd frame is exactly the same as if it would be scrolled by 0.5 pixel every frame in real interlace. Hmm, but then, this is more like a resolution reduction for the true interlace (the halfpixel-scrolling makes one type of lines, e.g. EVEN ones, obsolete). So this seems more like a transformation true (PAL)-interlace -> Only-ODD-lines-interlace.
Still... the brain must play a central role here! Nobody here who had the chance to do a direct comparison?
CF |
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ptoing
Registered: Sep 2005
Posts: 271 |
This effect has nothing to do with scanlines at all as far as I understand. It is purely optical (an illustion if you will).
I made some pictures of how I think it works.
I took my picture Yus Chunk and seperated it into it's odd and even lines (yes I know it is only 200 pixels high to begin with, but the effect still applys)
Now when condense them by taking out the blanks and animate them one after another, odd first you get this. You can see that the even frame seems to scroll even tho technically it DOES NOT. This is because due to being condensed the lines got shifted up by one, hence the fake scrolling. And this is also the reason you only need to shift the whole deal up every 2nd frame.
And because this has fuck all to do with scanlines you can also do this horizontally as well. |
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algorithm
Registered: May 2002
Posts: 702 |
When applying this to still images, you can still get some type of percievement of resolution increase (although it would be classed as color interlace only)
Try the same for a two white line circles at 400 pixels.
remove odd lines from first pic. even lines from second
then remove the gaps and flick them every frame.
What do you see. Percieved resolution increase, even though it is only color interlace. |
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Spinball
Registered: Sep 2002
Posts: 87 |
Quote: This effect has nothing to do with scanlines at all as far as I understand. It is purely optical (an illustion if you will).
I made some pictures of how I think it works.
I took my picture Yus Chunk and seperated it into it's odd and even lines (yes I know it is only 200 pixels high to begin with, but the effect still applys)
Now when condense them by taking out the blanks and animate them one after another, odd first you get this. You can see that the even frame seems to scroll even tho technically it DOES NOT. This is because due to being condensed the lines got shifted up by one, hence the fake scrolling. And this is also the reason you only need to shift the whole deal up every 2nd frame.
And because this has fuck all to do with scanlines you can also do this horizontally as well.
or vertical+horizontal(=diagonal) and you get crossbows 640x400 from krestage2 |
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MagerValp
Registered: Dec 2001
Posts: 1060 |
Half pixel scroll on the C64 gives just as real a resolution increase as interlaced video modes on the Amiga. Interlace works because our brain merges the two fields, but it's wrong to call it an illusion. |
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ptoing
Registered: Sep 2005
Posts: 271 |
Well, it kinda is an illusion tho, just as animation is an illusion. Those things do not "move" either, it's just still images played after another and that makes them LOOK as if they move = illusion. |
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Krill
Registered: Apr 2002
Posts: 2854 |
Doesn't Amiga's interlace also scroll the whole other picture by half a pixel in y-direction? |
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Oswald
Registered: Apr 2002
Posts: 5028 |
mager, to my knowledge the c64 only uses the odd or even frames, there are no halfpictures whatsoever. while the amiga does really use odd/even fields. |
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Radiant
Registered: Sep 2004
Posts: 639 |
Krill: Halfpixel scrolling is possible on the C64 as well, on a moving image. Kinda the point of the whole thread. :-) |
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