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Forums > C64 Coding > Half pixel shifting
2005-11-21 08:13
Twynn
Account closed

Registered: Nov 2005
Posts: 9
Half pixel shifting

First of all: It's good to see that the C64-scene is still alive.
I kinda left the scene about ten years ago but after accidently crossing this site I got interested a bit again. Downloaded some demo's to see what happened since I left and I was quite amazed. Not those ugly 8x8 modes anymore, but good looking demos.

Anyway, when I was watching krestage I saw this intro for each demopart which used this high-resolution text which is said to use half pixel shifting? I'm still familiar with the normal vic-tricks, but this one made me curious.

Now I wonder how this is done. Is it just a visual trick or has the vic really some possibility to do half pixel movements or something?
 
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2005-11-21 08:56
Oswald

Registered: Apr 2002
Posts: 5094
I understand then. In short this is the same as IFLI interlacing, or as in the demo 400, which doubles the vertical resolution. But doing this with a diagonal scroll you may *think* that you doubled both resolution. As the displayed graphics only alternates between 2 of a kind, its not even virtually 640x400 imho, as to really display the amount of data needed you would need to display 4 kinds of gfx.
2005-11-21 09:33
JackAsser

Registered: Jun 2002
Posts: 2014
IFLI is not the same since in IFLI you actually shift half a multicolor pixel, thus you don't have to scroll the image to get the impression of higher resolution, you actually get true interlacing in IFLI.
2005-11-21 09:47
Twynn
Account closed

Registered: Nov 2005
Posts: 9
Ok, thanx all.

Just a little interlace trick.. Well, still nicely done.

JackAsser: isn't IFLI actually more ment for producing more colors instead of a higher resolution?
2005-11-21 10:00
JackAsser

Registered: Jun 2002
Posts: 2014
Twynn: If you shift half a pixel you get higher resolution, if you don't shift you get color blending, that's basically it when it comes to interlacing. However, the artist may use interlacing as a means of color blending if the pixels are put correct.
2005-11-21 11:20
algorithm

Registered: May 2002
Posts: 705
Doesn't really matter if it is a genuine VIC trick or illusion. As long as it gives the effect, that is all that matters.

Some other examples are alternative interlace methods which seem to reduce flicker (line interlacing or cross hatch)
2005-11-21 11:30
Oswald

Registered: Apr 2002
Posts: 5094
anyone knows of a ifli pic where each line is shifted to the opposite direction ? I wonder if that method is ufeful.
2005-11-21 11:46
chatGPZ

Registered: Dec 2001
Posts: 11386
oswald: i tried this a (long) time ago...it actually improves the quality of the interlace quite a bit (depending on the picture ofcourse). its a simelar thing with evening out the luminance of both half frames. the first will improve horizontal color blending (since the picture will be displayed in a "checkerboard" style all the time) and the second will reduce flickering.
2005-11-21 11:49
WVL

Registered: Mar 2002
Posts: 902
Quote: anyone knows of a ifli pic where each line is shifted to the opposite direction ? I wonder if that method is ufeful.

not really IFLI, but i think HCL's Interruptus Retriggerus is a good example? (the part with the FPP logo)
2005-11-21 11:52
enthusi

Registered: May 2004
Posts: 677
Im a mere 'watcher' of those effects I admit :)
But IMHO what groepaz mentioned last is the most important thing about any interlace mode (unless its displayed with a beamer or my green-monitor :).
Well - my post was pretty obvious but I still wonder about people generating greyshades by black+white pixels etc. Must be some weird converter around somewhere...
...or the average graphician is too stoned to recognize and/or care
2005-11-21 12:00
algorithm

Registered: May 2002
Posts: 705
Try out my HOI converter. It takes a truecolor image and converts it to 192x200 hires according to the selected mix colors rather than the C64's 16 colors. Horrible flicking on anything other than a tv though.
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