Tape Vs. Film

Discussion in 'Archived Threads 2001-2004' started by John Meringolo, Feb 21, 2002.

  1. John Meringolo

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    CAN SOMEONE HELP ME ,I DO NOT UNDERSTAND THE REAL DIFFERENCE BETWEEN FILM AND TAPE . I THINK I HAVE THE QUESTION CORRECT.I SEE IT ,THE COMPARISON,USED OFTEN WHEN TALKING ABOUT PROG SCAN DVD PLAYERS .THANK YOU FOR ANY HELP.
     
  2. Vince Maskeeper

    Vince Maskeeper Producer

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    John,

    Could you be a bit more specific?

    You don't understand what is difefrent about the processes of tape vs film... or are you asking about the quality differences?

    There is often the claim of making video more "film-like" and this usually means smoother. Video has relatively low resolution, and very low refresh rates- so it pales in comparison with film.

    Things like Progressive scanning allows video to take on a more "film like" appearance- a smoother and softer look... but upping the rate that the fields refresh.

    Is there something specific you wanted to know about though? Could you give an example of what you're looking for?

    -V
     
  3. Allan Jayne

    Allan Jayne Cinematographer

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    Video (NTSC) is (approx) 60 frames per second for progressive scan, 60 half frames (30 sets, or fields, of odd scan lines alternating with 30 sets of even scan lines) per second for regular interlaced scan.
    U.S. movies are shot at 24 frames per second.
    In order to put the movie onto video, the film frames' contents are repeated in a 3-2-3-2 etc. pattern (3-2 aka 2-3 pulldown) which you can see when single stepping a VCR (if the source was a 24 fps movie) -- sixty steps but 24 unique views represnting the motion for each second of playing time.
    The significance as far as progressive scan goes, is that the initial decoding of the DVD (from MPEG decoder) yields interlaced video. For best results dealing with film source video the progressive scan player needs to always take pairs of odd-even fields that came from the same film frame to weave together to make each progressive scan video frame. The trick is to be able to find the matching fields amidst the 3-2 pulldown pattern; the finished progressive scan video will still have said 3-2 pulldown.
    On the picture tube, for interlaced video,the odd lines start to fade while the even lines are being drawn, and vice versa. The keen eye will see the resulting gaps particularly when following motion on the screen. With progressive scan scan lines are drawn twice as fast so fading is much less pronounced. The gaps between adjacent odd or adjacent even scan lines are no longer seen and the visual appearance is described as more resembling projected film as opposed to video.
    More:
    http://members.aol.com/ajaynejr/viddoubl.htm
     
  4. Rick Radford

    Rick Radford Supporting Actor

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    Allan,

    Since DVDs often come from a 24 fps film based source, can the 3:2 pulldown be done as a part of creating the DVD? Or is it always necessary for the 3:2 correction to be done as a part of playback?

    How can you know if a DVD is film based or video based? Does it really matter?
     
  5. Scott Page

    Scott Page Stunt Coordinator

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    I believe this is how it goes:

    The 3:2 pulldown is done during playback because interlaced and progressive players each handle it differently. Interlaced players may have some image overlap due to the conversion, while progressive scan players use complicated software to properly combine the frames during the pulldown that eliminates the image overlap.

    There are flags on the DVD that tell the player if its film or video. Setting your player on Auto-Detect usually works best. However, a very few, poorly done DVD's may have incorrect flags requiring you to force the DVD into one or the other. I have not come across any of those DVD's yet.
     
  6. Allan Jayne

    Allan Jayne Cinematographer

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    For film source DVD's the video is usually stored on the disk as "2-2 pulldown" interlaced (one each of the even and odd fields per film frame, 48 fields per second). Putting the full 3-2 pulldown on the disk (is possible but) consumes space unnecessarily and shortens the available playing time per disk. It is up to the player to recreate 3-2 pulldown to get all 60 needed fields per second for interlaced scan, and to turn it into progressive output if applicable. I am told that the first stage (MPEG decoder) outputs the video already as 3-2 pulldown interlaced, the second stage (de-interlacer) if present creates full frames for progressive scan. Also I am told that if the full 3-2 pulldown is recorded on the disk, that is considered a live video source as opposed to a film source.

    Flags in the video data tell the player which fields to repeat for interlaced output and which fields are first of a matching pair (the next one is the other half) for constructing progressive output.

    If the flags are absent or wrong, the player should (does not always) have alternate backup means (in its de-interlacer) of identifying matching field pairs for progressive scan full frames. The same mechanism, if present, that takes hints from the video (pixel analysis) to de-interlace non-film video properly will also pick up situations where flags are incorrect, and take over the proper constructing of the progressive scan.

    DVD players with good 3-2 pulldown flag sensing and also good backup handling of the de-interlacing should not require a manual selection for film versus live video optimizing.

    I am not sure how well single stepping through DVD reveals this but you can determine whether a DVD was 24 fps film sourced by recording it on your VCR and single stepping through the tape playback. Most commercial U.S movies are film at 24 fps, a few are 30 fps, home movies are 16 or 18 fps, a few movies are videographed with no film involved. The consumer has no choice so I don't think it can matter.
     
  7. Rick Radford

    Rick Radford Supporting Actor

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    >I am told that if the full 3-2 pulldown is recorded on the disk, that is considered a live video source as opposed to a film source.<

    That's interesting!

    Thanks for the info, fellas.
     
  8. John Meringolo

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    thank you , all the replies i eceived were a help. this site is great.
     

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