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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  • Anand Lal Shimpi - Monday, December 20, 2004 - link


    I should have made this more clear, I used the NVIDIA codec for NVIDIA's tests and I used ATI's codec for ATI's tests. I used Zoom Player for both of them.


    They never briefed me on anything like that but I can always ask :)

    Take care,
  • ViRGE - Monday, December 20, 2004 - link

    Thanks Crimson, but I'm talking about the video features, not the elusive cards themselves. ;-)
  • crimson117 - Monday, December 20, 2004 - link

  • ViRGE - Monday, December 20, 2004 - link

    I know this is an Nvidia article Anand, but could you get on ATI's butt about their lack of features too, and find out what's going on? When the X800 was launched, ATI was talking about decode acceleration for MPEG4 along along with some sort of encode acceleration(i.e. all the features NV promissed but never delivered on). I'm curious to know what happened to that, and if we're going to get something new out of ATI besides WMV acceleration.
  • gordon151 - Monday, December 20, 2004 - link

    I was wondering why AT's results were different than PCPers and just noticed they used MMC & 4.12 while AT used the nVidia codec and player for both cards tests.
  • Anand Lal Shimpi - Monday, December 20, 2004 - link


    I've asked numerous times, never gotten a response. I'll try again :)

    For those of you who are wondering, I have asked NVIDIA what their official statement is to early 6800 adopters, but that has also been met with no response.

    Take care,
  • Ytterbium - Monday, December 20, 2004 - link

    I'm dissapointed that the encode function never made it, that was a killer feature. Any idea if it will come?
  • Spike - Monday, December 20, 2004 - link

    Thanks for that! I have the BFG 6800 GT and on the BFG cd there is the nvDVD software. It's nice to know I can actually use the VP that I paid for!

  • Gatak - Monday, December 20, 2004 - link

    Here are some examples of interlacing artifacts when redering on a progressive screen:


    Most software DVDs either blend or remove one of the fields by some partial de-interlacing algorithm. nvidia's DVD decoder does it ok. The image is sharp but still leaves only half framerate.


    But in reality, half temporal resolution is lost. What should have been done is to render each field as a separate frame.

  • Anand Lal Shimpi - Monday, December 20, 2004 - link


    I wasn't aware that the 6800s are coming with NVDVD, in that case you are good to go. Just download the updated version (1.00.67 is the official version) from the website.


    The full system was configured as follows:

    Intel Pentium 4 570J
    Intel D915GUX Motherboard
    2 x 512MB DDR2-533 DIMMs
    Intel HD Audio Enabled

    Windows XP SP2 w/ DX9c

    Take care,

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