Hertz?

[dentalrep]

Can someone explain how this effects PQ? Interested in the Sony or Pioneer Players and one of their pluses is the fact they can output 24 hertz. So if some is kind enough to explain it to me I would appreciate it.

[phloyd]

Films are shot at 24 frames per second.

TVs (including most HDTVs) can only display things at 60 fps or multiples thereof.

Since that is not an integer multiple of 24, there is some motion artifacting.

Now that players are offering 24 fps output, if your display can display that at an integer multiple (say 48, 96 or even 120) then you should see smoother pans and motion.

But both your player and display need to do the right thing.

[Deciazulado]

Hertz means frequency, as in 1 Hertz is one cycle per second. (On-off state, flash per second, string vibration per second in a musical instrument, etc)

The sound movies you see in in a theater are shot with a camera that takes 24 pictures per second (frames per second or fps). But if you saw those pictures flashed 24 times per second you would see strobing or flickering (that's why they are called "movie flicks") so projectors have a 2-bladed, or sometimes 3-bladed, shutter that blocks the light hitting the frame 2 or 3 times a second creating 48 flashes per second (48 Hz) or 72 flashes per second (72 Hz), preventing the perception of strobing or flickering.

When the US NTSC TV system was made, 60 Hz was chosen, to be in sync with the AC line frequency (In PAL countries it is 50Hz), so TVs refresh the image 60 times a second displaying either 30 complete frames a second (30fps or 30p) split into two fields for 60Hz, or showing motion actually captured 60 fields a second (60 half frames or 60i). When displaying theatrical motion pictures, a 'conversion' is made by splitting the 24 frames into 48 fields and then inserting repeat fields in a 3:2 pattern so you end up with the 60 fields required for a 60 Hz flashing interlaced display. This creates slight motion judder for 24fps material.

Now we have LCDs and DLPs etc that display images in full frames (called progressive frames) instead of interlaced fields, usually at 60 fps (still 60 Hz). So the player's output can be either 60i or 60p. The display's output is always 60p (60Hz refresh rate) with these.

So if the original video was shot in true 60i (like live videotapes) a deinterlacer converts the 60i fields into 60p frames. If the 60i video is actually something shot in 30 frames per second (the Oklahoma! 70mm 30fps version, ads, videos, computer animations, etc) the frames are repeated twice to get 60p. If it is 24fps film the frames are repeated alternatively one twice, the next one thrice, to get the 60p, 60Hz refresh rate. This still is creating the slight motion judder for the 24fps material.

To prevent this judder, some displays can accept the pure 24 fps output from a player capable of doing so, without the 3:2 repeats. These displays then of course won't be displaying those signals with a 60Hz refresh, but with either a 48Hz or 72 Hz (or someday 120 Hz) refresh, by taking the 24 frames and repeating each twice (for 48p, 48Hz refresh rate) for smooth motion. Or three times (for 72p, 72 Hz refresh rate).

[Zinn]

Thanks phloyd & Deciazulado. Does this feature have a name (that the tv can display without judder)?

[Deciazulado]

1080 24p

Look for the specs.

Your player must output it, and your display must accept it. Some displays might also accept a 60Hz output from a regular player, recognize the 24 fps cadence and inverse telecine out the 3:2 and convert/display it at the correct 24p/48Hz/72Hz/96Hz/120Hz rates.

On the display side, just to make sure, confirm that it specifically plays 24fps content as 24. Not that it just accepts it, and then displays it at 60Hz. (Could happen!)

Manufaturers will probably come on with different catchy but confusing phrases on their own for the feature too.