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What does 30Hz mean? Why are they more frames per second in US rather than in Europe?

Discussion in 'TVs' started by myself, Nov 10, 2002.

  1. myself

    myself
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    Hi all,

    I have some questions if anyone can help me.

    Why are in TVs the frames per second more in the US than in Europe? I was reading that the frames per second in Europe is 25 FPS while in the US has changed to be 30 FPS.

    Also, does anyone know how many FPS are in other continents?

    Finally, when I say "the frame rate is set to 30Hz" does that mean that there are 30 frames per second?
    Does that mean that the screen is updated 30 times per second?

    Is it the same when I say that "fields are painted at a rate of 30 per second or 30 Hz?

    Any help appreciated.
    Many thanks.
    :confused:
     
  2. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Our mains is at 50Hz:
    Our TV system is interlaced (ie you get HALF a FRAME every 50th of a second)
    2 Fields = 1 Frame
    So UK is
    50Hz= 25 Frames per second, 50 Fields

    US mains is 60Hz
    Their TV system is interlaced
    60Hz= 30 Frames per second, 60 Fields.

    Hope this is a little clearer. No time for more in depth reply

    Gordon
     
  3. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    NTSC DVD's run at 30FPS......not 24....
    PAL DVD run at 25FPS ...not 26

    24Film frames is turned in to 60 FIELDS for NTSC using a telecine process lik tehis. First the 24Fullframes are interlaced to create 48 fields (with me so far...they show even lines one 60th then odd lines the next) So we're at 48 but we need 12 more to get to 60....so lets repeat every 4th field creating 12 more! This is called the 2:3 sequence

    For PAL it's even simpler. The interlace the 24 frames to create 48 fields then speed the film up so we see 2 extra fields a second. Check the running time of PAL and NTSC films and you'll find the PAL one is over faster.....

    Both these methods casue problems. NTSC suffers motion judder in pans due to the 2:3 sequence and PAL film source stuff usually has the pitch of voices/music incorrect due to the speed error....oh well....

    Gordon
     
  4. paperclip21

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    NTSC 24fps is converted to 30fps using a technique calling 3:2 pulldown.

    To get 30fps from 24fps you have to add 6 frames in 24, or 1 frame every 4:

    Frame 1 -> Field 1,2
    Frame 2 -> Field 3,4,5
    Frame 3 -> Field 6,7
    Frame 4 -> Field 8,9,10

    Where Fields 1-10 are the new 5 frames.

    An unfortunate side-effect is that this technique introduces stutter on smooth panning shots.

    HTH.
     
  5. myself

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    Thanks for the help.

    I understand now but I have confused myself.

    I understand that DVD NTSC films run at 24 fps the same as the cinema release and that PAL DVD has to speed them up to 26 fps. So what happens when a NTSC DVD is played on an NTSC TV why is it not running at 30 fps as the TV specifies?

    Many thanks.
     
  6. Xeonic

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    OK, here goes....

    Firstly 1 frame (or single image, if you like) is 2 fields.

    PAL is actually "sped up" to 50 fields per second not 26 - Gordon's phrasing meant film at 24 frames per second is turned into 24 x 2 fields per second = 48 fields per second.
    But pal needs 50, so the 48 is sped up ever so slightly by 2 fields per second to 50!

    Now about NTSC, the tv is running at 60 FIELDS per second, or 30 FRAMES per second. Saying fps in this circumstance will lead to confusion, due to obvious reasons.

    The reason you say a "standard" NTSC tv runs at 30 frames per second is because it is accepting the broadcast 60 fields per second signal! The TV puts the 60 fields (half frames) back together to make 30 full frames. A signal with the native 30 full frames is called progressive - one with the 60 fields interlaced.

    The process of combining the fields introduces unwanted visual effects. This is the reason a progressive signal should look better than its interlaced version.

    There are articles at www.progressivescan.co.uk which explain this whole process in more detail..
     
  7. myself

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    Many thanks for all your help.
    Really appreciated.
     

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