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30FPS displayed on a 200Hz monitor

  1. Mar 4, 2015 #1
    Hello!

    I have a PAL TV, and that means it is best for footage of 25fps and 50fps
    The TV's refresh rate is 200Hz



    Well, my questions are:
    What happens if I play an NTSC file on the TV? (≈30fps), since it doesn't go well with 200Hz much (isn't a multiple)...
    • I thought about how would the TV display such files, assuming and hoping that no frames are dropped.
    • I thought that if you copy a frame 7 times at 200Hz it is approximately 28fps, and if you copy a frame 6 times, it is approximately 33fps.
    • Since the average of them is about 30.95fps, it quite irritates me, as I tend to be quite perfectionist...
    • I wanted to calculate how much frames to play at 33fps and how much frames to play at 28fps (overall in a second) to achieve the closest result to 30fps, again, without dropping frames.

    I've made a sort of a assumption, which I have no idea if right or even close to reality, since my knowledge at math is quite basic.

    Here is the link to all the calculations I attempted:
    desmos.com/calculator/76jnihypub

    I hope it is understandable enough, and since I have a tendency to confuse between cycle time and frequency, I cannot tell if what I've done makes any sense, it could be absolute nonesense...

    If it is not even close, then please, I would like if someone could enlighten me and show me how should this be done.


    And as a side question, if anyone is familiar with this, what do TVs with various refresh rates actually do when given files whose frame rates don't have a common divisor with the Hz of the monitor?



    Thank you very much!
     
    Last edited by a moderator: Mar 4, 2015
  2. jcsd
  3. Mar 4, 2015 #2

    mfb

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    Why so complicated? Let a fraction p of images been shown for 6 frames, the other for 7 frames.
    Then the average number of frames per image is 6+p which means the average time of an image is (6+p)/200 seconds. This should be the same as 1/30 second, therefore 1/30 = (6+p)/200. And this has a nice simple solution.
    I don't know if monitors actually do this (you can get a better (more fluent) result if you mix the two images).
     
  4. Mar 4, 2015 #3
    B1%7D%7B30%7D%3D%5Cfrac%7Bp+6%7D%7B200%7D%5C%3B%5Crightarrow%5C%3Bp%3D%5Cfrac%7B2%7D%7B3%7D.gif


    Sorry if this is a silly question, but what exactly does p stand for?
    Do I have to do the same thing with (p+7)/200?
    If yes what should I do after, and what in conclusion is the best average frame rate?
     
  5. Mar 4, 2015 #4

    mfb

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    I don't see where you would get (p+7)/200 from. The average number of frames won't exceed 7.

    p=2/3 suggests to use 2 images for 7 frames and 1 for 6 frames. 3 images in 20 frames, or 30 images in 200 frames, which directly matches your frame rates.
     
  6. Mar 4, 2015 #5
    Wait so this is the method you mentioned that mixes the images?
     
  7. Mar 5, 2015 #6

    mfb

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    No. What I meant with "mixing" is something like this, but on a shorter timescale.
     
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