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50hz / 60 hz confusion

Discussion in 'LCD & LED LCD TVs' started by mattg, Sep 13, 2005.

  1. mattg

    mattg
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    hi all, I am confused about the difference between 50hz and 50 hz screen modes?
    Is there a difference in performance, or is it a region thing like pal or ntsc, or am i in the completely wrong ball park again.

    Thanks, Matt.
     
  2. Doctor Hades

    Doctor Hades
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    PAL is 50Hz and NTSC is 60Hz. NTSC gives a quicker refresh rate than PAL, upto 60 frames per second compared with 50. PAL has more vertical lines of resolution than NTSC, 576 compared with 480 I believe.

    So NTSC has a better refresh rate and PAL has better resolution, both of which are more noticeable on standard CRT TVs (e.g. NTSC is less flickery than PAL but the scanlines are more noticeable) than HD LCD TVs.
     
  3. sandstheman

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    the 50hz and 60hz is related to PAL and NTSC, traditionally, Pal has been 25 frames per second and NTSC is 30 frames per second - with flat panel displays the frames are being refreshed twice as fast as the frame speed so for Pal 1 frame is refreshed 2 times in 1/25th of a second. Hence Pal being 50hz (2x25) and NTSC being 60hz (2x30) - some CRTS support 100hz which is Pal again at 4 refreshes per frame - this is usually done to proivide smoother movement in the picture.
     
  4. Nick_UK

    Nick_UK
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    A PAL picture is made up of 25 "frames" a second made up of "fields" of interlaced pictures which are refreshed 50 times a second, but each "field" is only a half-picture made up of odd or even lines. In this way, less flicker is achieved with less bandwidth.

    These days with LCD and plasma screens, the frame and field information is fed to a memory store, and read out at a rate best suited to the display. The PC LCD display I'm currently using only has a refresh rate of 60Hz, which on a CRT screen would give flicker, but because of the way LCD screens actually display the pictures, no flicker is seen.
     
  5. mjcairney

    mjcairney
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    And the reason for that is that the UK mains supply is 50Hz whilst the US one is 60Hz.

    Cheers,

    Martin.
     
  6. Doctor Hades

    Doctor Hades
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    Something I've always puzzled about is that PAL 50Hz means that console games can run at 50 frames per second, right? Well on a normal TV the image is interlaced, that is the even lines are drawn in one refresh and then the odd lines in the next (which results in tell-tale flicker on standard TVs as the even lines are starting to fade by the time the odd lines have finished being drawn). So far so good.

    But if a PAL TV only refreshes 50 times per second and the odd and even lines are drawn in alternative refreshes, does that mean that 50 frames per second is actually 50 half-frames per second (odd then even lines) or 25 full-frames per second? :confused:
     
  7. ianh64

    ianh64
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    I think the answer is yes - PAL is 25 frames per second, 50 fields per second. A field is what you are calling a half frame.

    PAL progressive is 50 frames per second since a field is full frame.

    Taking it one step further, 720p/50 is 50 frames per second but 1080i/50 (also indicated as 1080i/25 - confusing isn't it?) is 25 frames per second, 50 fields per second. ie 1/2 the spacial resolution of 720p but approx 2.25x the visible resolution which at the end of the day mean that they pretty much have the same amount of information per second.

    -Ian
     
  8. mattg

    mattg
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    thank chaps :D
     
  9. Rob1698

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    On an LCD the refresh rate only determines how many frames per second can be shown, not how much it flickers. (that is determined only by the backlighting)

    Note that Philips has determined that this sample-and-hold characteristics of LCD actually causes the motion blur that some people complain about, and will re-introduce the flickering of the screen in the next model of their high-end LCD line (it was meant to be in the 9830, the successor of the 9986, but it has been postponed).
    This "strobing backlight" better matches the characteristics of eye and brain, and means the movement will appear smoother.
     
  10. Doctor Hades

    Doctor Hades
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    Thanks for that, Ian.

    One more question though. Most PAL console games run at 25 frames per second, e.g. Project Gotham Racing 2. That's 50 fields per second right. So what's the difference between a console game running at 25fps and one running at 50fps? Is 25fps actually 25 fields per second (12.5 frames per second)? :confused:
     

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