An Interlacing Primer

A big part of the PureVideo feature set are its de-interlacing capabilities, but before we explain what de-interlacing is we have to explain what interlacing is and why you would want to de-it. Let's say we wanted to display an animation and here we have one frame of that animation:

If the world were perfect we would just broadcast as many frames of our animation as we had, at a constant frame rate, and we would have accomplished what we set out to do. Unfortunately the world isn't perfect and when we first wanted to broadcast this animation there were significant bandwidth limitations both on the transmitting and receiving side, preventing us from sending one complete animation frame at a time. One solution to this problem would be to divide up each frame into separate parts and display those parts in sequence. If the sequence is fast enough, the human eye would be hard pressed to notice the difference. So let's do it, we take our original frame and produce two separate fields, each with half of the resolution of the original frame:


Field 1


Field 2

And we're done, what we've just briefly described is how interlaced television came about. Interlaced NTSC TV (the North American standard) works by displaying 60 interlaced fields per second relying on the human eye to do a bit of blending work on its own, making two half resolution fields appear to be a single full resolution frame. More recently there has been a push away from interlaced TVs to non-interlaced displays, which is a wonderful step towards improved picture quality but not without creating a whole new set of problems. Keep this basic introduction to interlaced TV in mind as we look at converting non-interlaced (progressive) content to an interlaced format and back again.
Index Frame Rate Conversion and You
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  • phusg - Tuesday, March 01, 2005 - link

    Has anyone found a 6600GT card manufacturer that bundles nvDVD including the DVD decoder yet? Reply
  • akozak - Tuesday, January 04, 2005 - link

    Hey Anand,

    Don't mean to poo-poo on your hardwork - but almost all of your images are using different frames.

    a) Galaxy Quest - differences in star placements, planet alignment

    b) Apollo 13 - head is shifted b/w images

    c) Friends - characters shift - legs are different locations etc

    In fact the only ones that look like they are the same frame show no differences.

    Have you looked at the difference in frames? If you took one frame before or one frame after on one card, would it match up to the other card's image you already have?



    Reply
  • b3roldan - Friday, December 31, 2004 - link

    hi, I'm using a vanilla 6800 from inno3d w/ Forceware 66.93.

    I was just wonderin if you guys were also experiencing problems I've had with these games or if t'was just me.

    Metal Gear Solid 2: Substance
    - Everything's black and white. Wondering if it has anything to do with nvidia's 0x32 Z stencil (shadowing technology).

    MAFIA
    - Walls are multi-colored, sometimes transparent

    I've just upgraded from a 9800PRO 128mb, which worked pretty well with these games.

    Just wonderin if there are others with the same prob... thx :)
    Reply
  • Gatak - Thursday, December 23, 2004 - link

    What nvidia or ATi ought to do is to prove a simplier interface and especially much better documentation on how to access the hardware directly.

    The GPU's are incredibly fast for lots of things. For example it would indeed be possible to do video encoding, photo manipulation effects (Apple core.image/video!) or even sound compression.
    Reply
  • jago25 - Thursday, December 23, 2004 - link

    Shame I'll never be able to use it..seeing as I don't use Windows.

    You can use a GPU to do anything. Might be a good idea to make it easier to do so rather than having to develop more codecs as that's a never ending job.
    Reply
  • hellokeith - Wednesday, December 22, 2004 - link

    The article really needs to be corrected per the 6800 PCI Express vs 6800 AGP. People are talking about this on numerous HTPC/AVS forums and being mislead. Only the PCI Express 6800 has the new silicon. Reply
  • karlreading - Wednesday, December 22, 2004 - link

    ive jumped through the other pages from a comment on page one, so if this has already been answered, lynch me now:
    anand said he knows of no manufacturer that bundles nv DVD.
    im pretty sure its on my bfg disc that came with me 6800GT OC ;)
    thats me sorted then.
    karlos
    Reply
  • mikepers - Wednesday, December 22, 2004 - link

    This should help:

    http://www.nzone.com/object/nzone_purevideo_requir...

    There's a link for the correct driver and the decoder and at the bottom a link which shows which cards support what. Sort of sucks that my AGP 6800 Ultra has less features then a 6600 card but it is what it is...
    Reply
  • CrystalBay - Tuesday, December 21, 2004 - link

    Remember Buy.com ? Where are you Harvey!!!! Reply
  • tfranzese - Tuesday, December 21, 2004 - link

    mcveigh, he provided the link to where you could find that for the ATi side of things. I'm curious about the S3 things, though it wouldn't surprise me if true. Reply

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