24p what is it thats better?

Malone

Active Member
I have searched on Wikipedia and on here but cannot find a laymans answer.

I am not techie and do not know the specifics so forgive me if this is not entirely correct.

As I understand it PAL Tv's run at 50hz, if you have a 100hz Tv then that is storing and replicating the previous frame to give you an improvement on the flicker.

So you are getting 50 or 100 frames per second, if this is the case why is there 'excitement' about the 24p playback. Surely this is slower and will result in more flicker?

Please would someone enlighten me in laymans terms.

Ta
Matt
 

twentyone

Novice Member
Most movies are shot at 24 frames per second, while TV is shot at 60 frames per second. Since TV shows are shot at a faster rate, TV sets need to be able to properly show this. Since 24 doesn't go fully into 60 (mathematically), 3:2 (or 2:3, can't remember how that goes) pulldown is needed to properly display the frame rate. The only problem is that juddering can occur when a camera pans, like in the drug store at the beginning of Layer Cake. It's pretty bad there. If your set will display 24p, you will have a more seemless picture.
 

Malone

Active Member
Ahh, so you're saying that displaying natively at 24fps negates the need for the equipment to adapt it to display it which allows a smoother image.

Thanks Tom, I assume my summary is correct?
 

Barcoing Mad

Active Member
No, 24fps needs the right equipment to recognise and display it correctly as a progressively scanned image at a whole number multiple of 24 fps, e.g 72.
 

Malone

Active Member
Little bit confused with that Barcoing. An example, one has a 42PZ80 and a PS3 with up to date firmware (I believe it can now output bluray at 24p) does this mean that the bluray image will be smoother?

Matt
 

NicolasB

Distinguished Member
I have searched on Wikipedia and on here but cannot find a laymans answer.

I am not techie and do not know the specifics so forgive me if this is not entirely correct.

As I understand it PAL Tv's run at 50hz, if you have a 100hz Tv then that is storing and replicating the previous frame to give you an improvement on the flicker.

So you are getting 50 or 100 frames per second, if this is the case why is there 'excitement' about the 24p playback. Surely this is slower and will result in more flicker?

Please would someone enlighten me in laymans terms.
All right, I'll try. :)

Unfortunately you're conflating several different phenomena, here - we need to try and separate them out.

First, let's think about flicker. Flicker is something which is only a problem if the screen image is actually flashing on and off. Old-style CRT displays work like this: each frame flashes up momentarily onto the screen, then fades to black. If that happens too slowly then there is visible flicker. However, a modern display (such as an LCD screen or plasma) doesn't work like that. Instead, the screen remains bright for the full duration of each frame. At the end of each frame the picture changes (hopefully quickly) from showing that frame to showing the next one.

So, basically, forget about flicker unless you're dealing with a CRT display. Flicker isn't in any way relevant, here.

The second thing you need to understand is that TV signals with a 50Hz frame-rate are only found in Europe. In America or Japan TV works at a 60Hz frame rate. For DVDs the frame-rate reflects the broadcast TV frame-rate, so Europen DVDs tend to be 50Hz, but American and Japanese DVDs are 60Hz. However, this doesn't apply to next-generation disc formats like HD-DVD and BluRay: there is no such thing as a 50Hz BluRay or HD-DVD disc. (They aren't exactly 60Hz either - more on that in a moment).

The third thing you need to know is that cinema film is normally shot at 24 frames per second. If you want to encode a 24fps film into either a 50Hz or 60Hz signal, you therefore have a problem, because neither 50 nor 60 is an exact multiple of 24.

The film on a BluRay or HD-DVD disc is actually encoded as 24 film frames per second. Ideally what we would like to do is simply output that as a 24Hz signal. The TV would then display each frame for 1/24th of a second before switching to show the next frame.

But, unfortunately, many televisions are not capable of accepting a 24Hz signal. In a case like that you have to feed it a 60Hz signal instead. To convert the film to 60Hz you have to show the first frame twice, then the second frame three times, then the third one twice, then the fourth one three times, and so on.

This doesn't create flicker: there is no visible transition at all between the first and second repetitions of the first frame. But it does mean that the length of time each frame is being displayed on the screen for is no longer constant: some frames are shown for 1/30th of a second, and others for 1/20th of a second. This causes an effect called "3:2 judder". It is visible on moving objects or on camera pans: what should be smooth motion seems slightly juddery because the object seems to be moving alternately faster and slower.

(It is worth mentioning that there are a lot of different effects which could reasonably be described as "judder", and I suspect that the majority of the people who complain about 3:2 judder are actually seeing something else. Many people are unable to see 3:2 judder at all. But, for those who can, proper 24Hz output fed to a TV that accepts the signal is a better option.)
 

Toadus

Well-known Member
What great explanation. :smashin:

I was blaming this whole 24p thing for juddery scenes, when it turned out to be a different story completely, as I was experiencing the same issue with 24p on or off... IMO, as 24fps is fairly slow, when you have scenes which pan, you can't help but notice the lack of smoothness, but it's not the 3:2 pulldown, it's just simply the slow framerate and how it looks on a LCD TV.
 

choddo2006

Novice Member
What great explanation. :smashin:

I was blaming this whole 24p thing for juddery scenes, when it turned out to be a different story completely, as I was experiencing the same issue with 24p on or off... IMO, as 24fps is fairly slow, when you have scenes which pan, you can't help but notice the lack of smoothness, but it's not the 3:2 pulldown, it's just simply the slow framerate and how it looks on a LCD TV.
That's possibly true but generally movies are shot with a maximum pan speed limit that tries to avoid that sort of judder. In the cinema of course, the physical size jump between one frame & the next would be huge.

Depending which LCD it is, it's quite possible it's doing an internal 3:2 pulldown job on it & showing it at 60Hz. I believe Sony's more expensive screens and the latest Samsungs (not sure on the new Viera LCDs) do a proper job of it
 

Tarbat

Well-known Member
Couple of points/questions:

1. If your TV can only handle 50hz, then a Bluray player needs to FRC from 24 to 50, which casues even worse juddering problems.

2. Are there any Bluray players yet that can simply speed-up from 24fps to 25hz, and then double that to 50hz for output?
 

NicolasB

Distinguished Member
That's possibly true but generally movies are shot with a maximum pan speed limit that tries to avoid that sort of judder. In the cinema of course, the physical size jump between one frame & the next would be huge.

Depending which LCD it is, it's quite possible it's doing an internal 3:2 pulldown job on it & showing it at 60Hz. I believe Sony's more expensive screens and the latest Samsungs (not sure on the new Viera LCDs) do a proper job of it
Toadus' specific problem was what might be called "LCD judder" - the fact that the picture remains on the screen for the full duration of the frame and then switches, not quite instantaneously, to the next. This means that successive frames are displayed very close together, with some overlap, so you have the perception of seeing both frames on the screen at once. In his case the effect was more obvious on 24p material than it was in a 60p game, presumably because the 60fps game had smaller differences between successive frames.

See http://www.avforums.com/forums/showthread.php?t=748006 starting at about post number 50.
 

Toadus

Well-known Member
I must confess, I now have the Samsung 6 series, and with the Motion Plus off, BDs look no different to what they did on the Sony D3500. If I turn 24p mode on or off, I notice NO difference whatsoever, and that's on either TV. Pan shots on BDs look awful IMO, because you see like a yellow smearish type of lag to the image. For example, in the film Shooter, there's a scene where the camera pans across a building rooftop where a police sniper is sitting. As the screne pans across, you can see almost 2 of the same policeman with later part of the image looking yellowish. Hard to explain really. If I watch the scene with 24p mode on or off on either TV, it looks no different. On the Samsung, if I turn the Motion Plus on, you get absolutely no doubling of the image, it's perfect, but there's the big downside to the unatural look you get, which is a shame. I reluctantly leave Motion Plus off for movies. However, for other material, it can actually look good IMO, and leads me to something else actually...

I have planet earth on BD. If I set my PS3 to auto-detect 24p, it turns it on for this BD. Motion looks just like as you would expect, poor quality during pans and the like. However, if I disable 24p mode, so it runs in 50 or 60hz (I can't remember which) it actually looks better IMO, as you don't get so much of the doubling, yellowish stuff during pans. I find this odd, because when watching BD movies, it makes no odds having 24p mode on or off. And back to the point about the Motion Plus, I think it looks great with planet earth. You almost feel like you are there on some of the close-up shots, as it gives that very real feeling due to the motion.

Just some further points... I don't get any of this doubling stuff when watching Freeview for example. I was watching some superbike stuff the other night, and it was perfect. I tried the Motion Plus on Low setting, and it looked even better. :) I get the problem a little when watching DVDs, but it's not nearly as prominent as with BDs.
 

NicolasB

Distinguished Member
If I recall correctly, Planet Earth was filmed on 720p video cameras - in other words it was actually filmed at 50 or 60 fps, but at lower-than-1080p resolution, and then converted to 1080i for encoding on BluRay. So I guess the BluRay player's auto-detect of 24p is getting it wrong in this case. 24p is only appropriate for material actually shot at 24 frames per second. (I'm not sure if the output should be 1080i video, or 1080p but with a different frame rate - it depends on how the transfer from 720p to 1080i was done).
 

choddo2006

Novice Member
Couple of points/questions:

1. If your TV can only handle 50hz, then a Bluray player needs to FRC from 24 to 50, which casues even worse juddering problems.

2. Are there any Bluray players yet that can simply speed-up from 24fps to 25hz, and then double that to 50hz for output?
There are no HDTVs that only handle 50Hz though
 

Jonesthegas

Active Member
Is it now common for modern displays to accept a 24p signal? And do they display it at 24Hz or double it to 48Hz?

Also, if you have a VP which coverts 24p to 48p, how may set will process that correctly and display it at 48Hz with no further interference?

Martin
 

NicolasB

Distinguished Member
Is it now common for modern displays to accept a 24p signal?
Quite a few high-end screens do. Cheaper ones tend not to.

And do they display it at 24Hz or double it to 48Hz?
There would be absolutely no visible difference either way (unless you're talking about a CRT device).

Also, if you have a VP which coverts 24p to 48p, how may set will process that correctly and display it at 48Hz with no further interference?
Probably more than will accept 24p, but not that many more.
 

kingfats

Distinguished Member
Is it now common for modern displays to accept a 24p signal? And do they display it at 24Hz or double it to 48Hz?
Hi Jonesthegas. :)
Getting more common.
I think the latest Panasonics display 24p @ 48Hz :) the Pioneers display it @ 72Hz. :D
All the best.
 

Avi

Distinguished Member
Is it now common for modern displays to accept a 24p signal? And do they display it at 24Hz or double it to 48Hz?

Also, if you have a VP which coverts 24p to 48p, how may set will process that correctly and display it at 48Hz with no further interference?

Martin
Most decent new product will support 1080p/24 input. But it's worth double checking just to make sure they handle it properly.

The answer to your second question really depends on the particluar model of display. If it's LCD/LCOS based the display is likely to have a higher panel refersh rate than 48hz i.e. 96hz, 120hz to avoid motion smear for example. CRT also requires a high refersh rate to avoid the perception of flicker and DLP is different again because it's in a constant state of change. IFAIK the minimum refersh rate adopted by any tech when fed 24hz material if 48hz. I don't know if many of the newer displays support 48hz input and to be honest I don't really see any advantage in processing to 48hz pre display if the display properly supports 1080p/24.

AVI
 

choddo2006

Novice Member
Most decent new product will support 1080p/24 input. But it's worth double checking just to make sure they handle it properly.

The answer to your second question really depends on the particluar model of display. If it's LCD/LCOS based the display is likely to have a higher panel refersh rate than 48hz i.e. 96hz, 120hz to avoid motion smear for example. CRT also requires a high refersh rate to avoid the perception of flicker and DLP is different again because it's in a constant state of change. IFAIK the minimum refersh rate adopted by any tech when fed 24hz material if 48hz. I don't know if many of the newer displays support 48hz input and to be honest I don't really see any advantage in processing to 48hz pre display if the display properly supports 1080p/24.

AVI
Aye. Just one thing: I'm not sure an LCD refreshing at 96 will smear any less than one at 48. The crystals will just stay in the same place for twice as many cycles won't they?
 

Avi

Distinguished Member
Aye. Just one thing: I'm not sure an LCD refreshing at 96 will smear any less than one at 48. The crystals will just stay in the same place for twice as many cycles won't they?
The faster refresh is typically used in conjuction with other elements (see below) to reduce sample and hold effect. If the same frame was simply maintained for longer without any change there would not be any improvment with motion. I guess frame interpolation can also be added to the list. :)

"LCD Motion blur is a well known problem. Although many solutions have been proposed, some fundamental questions have not been answered yet. In this paper, we try to answer such questions. Specifically, we calculate the waveform and its blur width of a moving edge perceived on LCD screen for current LCD and the proposed four solutions of hold-type motion blur. We found that the slow response of current LCD is not a dominant factor of motion blur. The slow response of current LCD only contributes to 30% of the motion blur, while the hold-type rendering mode of LCD contributes to 70%. Therefore, fast LCD such as OCB itself does not significantly reduce motion blur. Fast LCD, on the other hand, is critical to the proposed three solutions of hold-type blur to avoid the ghosting artifact. With fast LCD, black data insertion and frame rate doubling can provide 50% reduction of motion blur. With both fast response LCD and fast backlight, backlight flashing can provide much higher reduction of motion blur. "

http://scitation.aip.org/getabs/ser...00036000001001590000001&idtype=cvips&gifs=yes

More background

http://scien.stanford.edu/class/psych221/projects/06/mmalkin/writeup.htm


AVI
 

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