3/2 Pulldown - What is it?

Discussion in 'Archived Threads 2001-2004' started by Colin A, Jun 9, 2001.

  1. Colin A

    Colin A Auditioning

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    I have read on this forum of 3/2 pulldown, can someone tell me what it is?
     
  2. Bob Dycus

    Bob Dycus Extra

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    Movies are made at 24 frames per second.
    Progressive Scan DVD players run 60 frames per second.
    3/2 pulldown repeats the first movie frame 3 times, the second 2 times, the third 3 times, the fourth 2 times, and on and on to produce 60 frames per second.
     
  3. RyanDinan

    RyanDinan Stunt Coordinator

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    Colin,
    While the above post is essentially correct, there are some other things to note.
    3-2 pulldown is the process APLLIED to the 24 frames per second of film, to adapt it to the 60 refresh cycles of video.
    As far as interlaced NTSC material (DVD, VHS, LD, etc..), this process creates fields of video (each field containing half the information of a total frame of film).
    However, each frame of film isn't sampled twice - Half are sampled three times (the third being a repeat of the first field). This causes intermixing of fields between 2 different frames of film. During normal interlacing, no one can really notice, but if a simple video de-interlacing scheme is used to de-interlace the video, it can cause some artifacts.
    Progressive scan DVD players that have a "film" mode, can figure out this 3-2 pattern, and combine only those fields that belong to the corresponding frame of film, preventing any mixing, essentially removing the 3-2 pulldown process. This is why it's also called "reverse 3-2 pulldown". Once the DVD player has this complete frame, it must apply 3-2 pulldown again, however, the whole frame is repeated 2 or 3 times (to match the 60 refreshes of NTSC video), and it isn't split into fields. This provides for an image with twice the detail, that is accurate to the original film frame.
    I'm sure if you do a search on the web, you'll find a more comprehensive explanation of this, with graphical aids...This can be a hard thing to grasp without pictures....At least it was for me [​IMG]
    Hope this helps,
    -Ryan Dinan
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    [​IMG]
     
  4. JohnHN

    JohnHN Stunt Coordinator

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    The classic web reference is
    http://www.hometheaterhifi.com/volum...e-10-2000.html
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