Display frame rates of "PAL" & "NTSC" DTVs

Discussion in 'Camcorders, Action Cams & Video Making Forum' started by dosdan, Feb 7, 2018.

  1. dosdan

    dosdan
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    I know a lot of DTVs and DVDs players are multi-system. So what's the deal nowadays with DTV frame rates. I presume an "NTSC" DTV will using display frame rates which are multiples of ether 59.94Hz or 60Hz, while "PAL" DTVs will be using multiples of 50Hz.

    But what about:
    NTSC DVD -> PAL DTV
    PAL DVD -> NTSC DTV

    Assuming that the DVD player is not doing an output frame-rate conversion, I presume that the display frame rate is always a multiple of 59.94/60Hz for a NTSC DTV and a multiple of 50Hz for a "PAL" DTV. So the Display rate itself is not changed, regardless of the source frame rate, and the DTV does an internal frame-rate conversion before displaying. Otherwise there might be banding/strobing issues playing back 60Hz material under 50Hz lighting. Is this correct?

    Dan.
     
    Last edited: Feb 7, 2018
  2. grahamlthompson

    grahamlthompson
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    Modern European sets will synch at 24Hz 50Hz and 60Hz (and multiples). US sets normally only do 24Hz (Blue-ray) and 60Hz. Ambient lighting has no effect on TV, they generate there own lighting. The older flourescent type use a high frequency back light source.

    Flicker is only a issue when using a 6oHz camcorder/phone with a lighting source that goes off at every voltage zero at 50Hz (Flourescent). Incandescent and LED bulbs don't flicker.

    If you try a film a 50Hz display with a phone that uses 60Hz the picture looks very jerky.
     
  3. 200p

    200p
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    One way to find out the actual refresh rate I think is to use a calibrator but those are expensive (eg. CR100, which costs thousands - I don't have one - seems to sync to the refresh rate of the display in one video and says it's refresh rate in the software (just above 120Hz when synced to a particular US TV in a video). One site says it syncs to refresh rates "between 10 and 500 Hz".

    I suppose the other way would be to film the display at a high enough frame rate and count the refreshes of the screen in the video of it (taking into account the shooting frame rate & seconds elapsed)?

    Is there no simpler, cheap way of determining the actual refresh rates the TV is currently outputting?
     
    Last edited: Feb 27, 2018
  4. dosdan

    dosdan
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    What about a stroboscope?

    AU Ship Landtek DT2350P Handheld Stroboscope Strobe 50~12000 FPM Flash Analyzer | eBay

    Dan.
     
  5. 200p

    200p
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    Thanks. Though I'm not sure whether or not that would do it. It says its for "measuring rotational speed of a rotating object, reciprocating, and oscillating or vibrating objects, such as cams, propellers, fan blades...". I'm not sure whether it could measure the TV refresh rate (eg. by syncing to particular line(s) of the screen being drawn?).
     
  6. dosdan

    dosdan
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    It's an unsynchronised flashing light. As the freq of the flashing light approaches the refresh rate of the screen, I think you'd see a horiz. black line. If the light was twice the freq, there would be two black lines. If there's a single line and it's stationary at the top or bottom, I think the two freqs are in sync.

    Another way. Shoot the TV screen with camcorder operating at "60fps" (actually 59.94fps.)
    I've just shot a few seconds of a PC monitor display with a 60HZ refresh rate, with a V770 running first at 1/50s shutter speed @ 50fps, and then 1/60s @ 59.94fps. These two clips are then combined, one after the other, and rendered to two MP4 videos, 50Hz & 59.94Hz. (They're actually "fps", but I've called them "Hz" to differentiate them from the original shot MP4s.)

    You can see, regardless of which rendered version you play back, that the 50fps capture of a 60fps monitor has an obvious beat, whereas the 59.94fps capture doesn't.

    50Hz version: https://dl.dropboxusercontent.com/s/md4s3gxihfg4sv3/59.94Hz.mp4

    59.94Hz version: https://dl.dropboxusercontent.com/s/vtdqmtd1lra9ehw/50Hz.mp4

    Dan.
     
    Last edited: Feb 28, 2018
  7. 200p

    200p
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    Thanks. Maybe the stroboscope could be used then.
    Also, in the post the "59.94Hz version" link currently points to the same link as the one above, named "50Hz.mp4".
     
  8. dosdan

    dosdan
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    Fixed.
     

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