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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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enthusi
Registered: May 2004
Posts: 677 |
movement in simplified, cartesian space = dR/dt = change of position in specific amount of time :o)
No need for illusion here.
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MagerValp
Registered: Dec 2001
Posts: 1078 |
Quote: 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.
It's like I'm talking to a brick wall here...
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Original progressive gfx (2x4 pixels):
**
##
..
__
Progressive PAL display using fake interlace, scrolling up 25 pixels per second:
E1 O1 E2 O2
** ##
** ##
** ## .. __
** ## .. __
.. __
.. __
Interlaced PAL display using real interlace, scrolling up 25 pixels per second:
E1 O1 E2 O2
##
** ##
## ** __
** ## .. __
** __ ..
.. __
..
So, to my conclusion fake interlace on the c64 is just color blending anyways, scrolling or no scrolling, but scrolling gives seemingly a better result, where as a true interlaced display give a true 50hz motion in half
pixels.
@MagerValp, exactly what did I misunderstood?
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Radiant
Registered: Sep 2004
Posts: 639 |
JackAsser: Compare the half pixel scrolling interlaced screen of a C64 with a static "true" interlaced PAL screen and you will see that there is no difference in how the actual interlacing is performed (i.e. half pixel offsets). A scrolling "true" interlaced screen looks different of course. The scrolling is only there to make it possible to fake the sub pixel screen positioning, thus achieving the same resolution you can get with true sub pixel positioning and a static screen.
In practice it's colour blending, but you have to look at the math behind it as well. Counting the interlacing offset per frame gives us a variance of 0.5 pixels - which is why it doubles the percieved resolution, just like "proper" interlacing. |
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JackAsser
Registered: Jun 2002
Posts: 2014 |
Quote: JackAsser: Compare the half pixel scrolling interlaced screen of a C64 with a static "true" interlaced PAL screen and you will see that there is no difference in how the actual interlacing is performed (i.e. half pixel offsets). A scrolling "true" interlaced screen looks different of course. The scrolling is only there to make it possible to fake the sub pixel screen positioning, thus achieving the same resolution you can get with true sub pixel positioning and a static screen.
In practice it's colour blending, but you have to look at the math behind it as well. Counting the interlacing offset per frame gives us a variance of 0.5 pixels - which is why it doubles the percieved resolution, just like "proper" interlacing.
Hmm I c. And sorry for my post being messed up...
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ChristopherJam
Registered: Aug 2004
Posts: 1409 |
OK, let's try a diagram, and I'll slow things down by a factor of 25 so you can see what's going on.
Here's what hydrophilic's technique looks like:
Here's what the half pixel scroll technique (as used in LT3 etc) looks like:
Note that in both cases, every second frame you see all the odd lines of the original double height image, and every other frame you see all the even lines. Also, in both cases, if your eye is following any movement of the letter (none in the first case, a continuous motion in the second), the missing lines appear between the lines you just saw.
I don't see how either case can be claimed to be higher resolution or more 'real' than the other. The sole advantage of the new technique is that you can display the image without having to scroll it. |
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Radiant
Registered: Sep 2004
Posts: 639 |
That is not how the scroll technique in i.e. LT3 looks like. There is no space between the lines. |
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ChristopherJam
Registered: Aug 2004
Posts: 1409 |
That depends on how your monitor's dot pitch compares to the line spacing.
I zoomed both images by a factor of two so that two rows of pixels in your web browser is equivalent to one row on the c64 - no other way to display the interlaced version correctly.
Here are some greater zooms, with blurring to simulate raster beam spread:
 (lt3)
 (hydrophilic)
Does that make it any clearer? |
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Oswald
Registered: Apr 2002
Posts: 5094 |
on the above the hydrophilic looks like true "half" line lace. |
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ChristopherJam
Registered: Aug 2004
Posts: 1409 |
Do you at least concur that each technique shows the same number of pixels each refresh?
When you look at one of hydrophilic's images, the eye constantly looks at the same point of the screen, so the odd lines project on to your retina between where the even lines appeared on the previous frame.
When you look at a letter in the scroller on LT3, the eye pans up the screen at a continuous speed, so again the odd lines project on to your retina between where the even lines appeared on the previous field. (not something that happens when you watch the slowed down version, as each field is being displayed dozens of times instead of just flashing up once, so the impression of continuous motion is lost).
I could add a red cross over the the LT3 image showing where your eye looks if anyone wants it...
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