NVIDIA Enables PureVideo on GeForce 6 GPUsby Anand Lal Shimpi on December 20, 2004 1:22 PM EST
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An Interlacing PrimerA 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:
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.