A Brief Look at De-Interlacing Modes

The process of taking interlaced content and displaying it in a non-interlaced form is often referred to as de-interlacing (for obvious reasons). There are two basic methods of de-interlacing, commonly known as "bob" and "weave."

Bob de-interlacing is more technically referred to as linear interpolation and it simply fills in the missing lines of resolution by interpolating between the resolution lines that are available. This interpolation form of de-interlacing is particularly useful if there are a lot of solid colors on the screen and if the decoder screws up and decides to combine two fields from different frames.

Weave de-interlacing, as the name implies, simply combines alternating lines of resolution from two separate interlaced fields. Using either method individually is generally not the best way of doing things, but thanks to the decent amount of power in today's PCs more sophisticated algorithms can be implemented to dynamically switch between bob and weave on a per pixel basis within a frame (usually referred to as adaptive per pixel de-interlacing).

NVIDIA's PureVideo supposedly takes adaptive per pixel de-interlacing one step further with what they call Spatial-Temporal de-interlacing. The idea here is that normal per pixel adaptive de-interlacing uses data from fields within a single frame to essentially fill in the blanks. NVIDIA's Spatial-Temporal de-interlacing can use data from fields in other frames to improve de-interlacing quality. We'll have to see if this ends up improving quality or not in our tests later in the article.

Frame Rate Conversion and You NVIDIA's PureVideo Driver and Encoder
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  • Rand - Monday, December 20, 2004 - link

    Anand- Could you provide the details on what the test platform in use was?
    You mentioned the processor of course, but it would be appreciated if you could disclose the other components in use.

    Thanks.
  • Spike - Monday, December 20, 2004 - link

    But the 6800's come with NVDVD (at least mine did), isn't that basically their decoder? Other users are reporting their new (just recieved today) 6800 GT's coming with the DVD decoder on CD.

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

    NVIDIA's DVD decoder has always been $20, unfortunately I don't know of a single manufacturer that gives away their DVD decoders for free.

    The WMV9 acceleration can be had without the DVD decoder, however that you will have to wait on Microsoft for as WMP10 needs to be updated.

    The features right now are mostly for HTPC enthusiasts who want the image quality benefits offered by PureVideo.

    Take care,
    Anand
  • Spike - Monday, December 20, 2004 - link

    I am still confused on the "free" comment. If I have to pay $20 to enable a feature that was supposed to come with my 6800 GT, how is that free?

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

    How to enable WMV9 hardware acceleration on ATI cards:

    Note: WMV9 acceleration has been disabled until Microsoft issues a new patch for WMV9. To enable this with other versions of Catalyst (with some rendering errors), RUN regedit -> HKEY_LOCAL_MACHINE -> SYSTEM -> CurrentControlSet -> Control ->Video and find your ATI reg value. The key to update is DXVA_WMV = 1

    Take care,
    Anand
  • gordon151 - Monday, December 20, 2004 - link

    #16, It does. It just doesn't have the full capabilities that it was advertised as having. If you look at the descriptions you'll see only the 6600 AGP/PCI-E and 6800 PCI-E have use of the full capabilities of the encoder.
  • Klaasman - Monday, December 20, 2004 - link

    I don't see on Nvidia's website where the 6800GT does NOT have PureVideo capability. They say all Ge Force 6 series.
  • OriginalReaper - Monday, December 20, 2004 - link

    why couldn't *those* sites shut down next week instead :-\
  • Gatak - Monday, December 20, 2004 - link

    There are some facts missing when it comes to differences between interlaced and progressive video.

    NTSC TV broadcasts are recorded at 60fps, not 30fps. (PAL is 50fps). Each field is recorded after eachother in time. There is a 16.7ms delay between each field.

    If you were to de-interlace two fields into one frame you would loose half of the temporal resolution! This is a big mistake - especially for fast moving things like a football or hockey game.

    A proper de-interlacing method would render each field as a separate frame (like a TV does!), not blend or discard fields.

    24fps content, on the other hand, need to be converted to fit the 60fps NTSC (or 50fps PAL). It is nasty and should be banned. A DVD/MPEG-2 video is perfectly capable of storing 24fps progressive.

    So, what we want is to render 24fps content as 24fps progressive and TV content as 60fps progressive.

    Remember, a TV is already interlaced. There will be no problems with interlaced content because each field is rendered consecutively. It is only on a computer monitor which is progressive where we need to do field deinterlacing.
  • SlinkyDink - Monday, December 20, 2004 - link

    How can we enable hardware acceleration on our ATI cards now? (I believe its a registry edit)

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