Understanding link between FPS and Hz refresh rate.

Discussion in 'General TV Discussions Forum' started by elsmandino, Nov 7, 2018.

  1. elsmandino

    elsmandino
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    I am currently looking at a new TV and note that a lot of the new TVs are offering 120hz (my current TV offers 100hz, which Samsung was pushing as the latest big thing at the time).

    Can anyone possibly help me understand why this makes any difference, please?

    I have done a bit of Googling on the subject and have just confused myself more than before.

    I was under the impression that video, to trick the eye into seeing smooth motion, needs to be seen at 24fps.

    I remember reading that for historic scientific reasons, TVs used to output at either 50hz or 60hz (the difference being that there is a difference in electric systems among countries).

    This is all fine, but if a TV screen is refreshing 50 or 60 times a second and the video is only playing at 24fps, why would you need to then go to 100 or even 120hz (I could understand a change if the refresh rater were less than 24fps)?
     
  2. zeppelino

    zeppelino
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  3. grahamlthompson

    grahamlthompson
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    Because 24 or 48 isn't a factor of 50 or 60. Replaying a 1080p24 stream on a TV that doesn't support 1080p24 requires the sending device to use a drop frame system to create a stream the TV can lock on to. This produces a jerky effect as you see when playing back blu-ray on a older TV that isn't 1080p24 compatible.

    100Hz is a gimmick You need a refresh rate that is a multiple of 24 (normally 23.976 fps)
     
  4. EndlessWaves

    EndlessWaves
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    FPS and Hz are both the number of images per second, it's just convention to call the content's rate FPS and the TV's rate hz.

    100hz and 120hz are the same thing among modern TVs, they all support both sets because European TV uses 25/50fps while US and Japanese services and devices use 30/60fps. TVs will also run at lower refresh rates like 25, 30, 50, 60 and so on.

    Actual video comes in anything between 23.976fps and 60fps.

    Higher frequencies are partly to support devices that can top high quality motion with 100 plus frames per second (primarily PC gaming). Mostly though, they're used with an image processing feature called motion interpolation that creates intermediate frames between the ones in the source to try and improve motion quality.

    Motion interpolation is something of a divisive topic as some people hate it while others find it brilliant. It doesn't always get it right so it can create artefacts and the quality of the algorithm varies between manufacturers and models.

    24fps is a particular source of arguments. It's an old standard that produces lousy motion, you have to add lots of blur in the video frames to make it appear smooth. The unreal feel of this blurriness has become associated with the cinema though, so it's still favoured by many film makers.

    Even 50/60hz TVs offer motion interpolation to bring the fluidity closer to real life, but some people find this jarring or prefer to watch it as the director intended. It's often known as the soap opera effect, as the blurry action scenes of a typical film become almost sharp as the motion in a soap opera.
     
  5. elsmandino

    elsmandino
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    Thanks for the brilliant explanations - I have heard of the soap opera effect, before, but completely understand the implications of it now.

    One of the TVs that I am currently looking at is the Hisense 55U7A, which is supposed to have a native 120hz resolution.

    I can see how the 24fps is remedied by this but does this not, then, cause problems with viewing UK TV - i.e. 25/50 fps is not a multiple of 120?
     
  6. EndlessWaves

    EndlessWaves
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    No, because the TV can run at 100hz as well.

    I don't quite understand the factors that mean it's challenging to get an 120Hz LCD to run at 24hz but not 100hz.
     
  7. elsmandino

    elsmandino
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    Right - now I am slightly more confused.

    How many hz can an average modern TV natively operate at?

    Am I correct in thinking that all TVs sold in the UK have to support both multiples of both 50hz and 60hz - so why the Hisense I mentioned would play at both 100hz and 120hz?
     

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