60i vs 30p vs 24p

[Sean James]

I wonder if there is a good source to tank up on these technical basics.

[Dave Rosky]

Originally Posted by Sean James

I wonder if there is a good source to tank up on these technical basics.

I didn't find a single place with a clear explanation of everything, but after looking around a lot, here is a really terse summary of the basics:

- Most newer TV's are progressive with a 60Hz referesh rate.

- A few TV's (e.g., Pioneer Kuro, but I can't guarantee that) have a few additional refresh rates that help with smoother (i.e., non-pulldown) display of 24P. These are usually either 72Hz or 96Hz, which are multiples of 24.

- A very few (maybe none at this point) can refresh at 120Hz, which is sort of a magic number because it is a multiple of both 24 and 30.

- A TV that refreshes at 60 Hz will deinterlace 60i material, and then display each deinterlaced frame twice in a row to get the 60Hz refresh rate. This is why on most progressive TV's, unlike older CRT's, 60i material doesn't necessarily have smoother motion than 30P

- A TV that can only refresh at 60Hz can only play 24P that has been pulled down to 60i, which normally happens in the DVD player. 2 out of every 5 frames will be interlaced in a way that contains a field from one 24P frame and a field from another 24P frame, so they don't necessarily deinterlace well, which is why such material won't look as good as 24P material on a TV that can change its refresh rate and display 24P with a "pure" pulldown like 3:3 or 4:4.

I'm a newbie to this too, so anyone please correct me if I'm wrong about any of this - I'd love to know so I can understand it more fully.

[Aaron Courtney]

Looks pretty good Dave. I'll only add that, as some people have found out with the Sony Bravia's in particular, that you have to turn OFF the 120Hz smooth motion in order for the display to natively process 24P material, which obviously is quite illogical, LOL. Also, there are issues with "forcing" the entire chain to properly handle 24P, which only creates more confusion regarding this technologically complicated topic.

What would be absolutely ideal (outside of the stupid BDA revisiting its spec to reflect current trends in videography), is if every progressive display had the intelligence in its video processing chipset to natively process every conceivable format. Then you wouldn't need to spend $1K-2K on a killer BD player with all the bells and whistles. All you would need, essentially, would be a $50 player capable of reliably transferring what is on the physical media over the wire to the display which would then be processed accordingly - in essence, nothing more than a dumb transport mechanism ala a $15 PC CD-ROM drive. This would also prevent any AVR from screwing up the video stream over HDMI on its way to the display. <--another serious issue people are beginning to discover.

Maybe we'll get there someday, but I'm not holding my breath.

One other thing that I'll add that I found particularly interesting is that 1080/30P is actually found in the ATSC standard for broadcast television. So perhaps there is hope after all.

[Ron Evans]

Another unknown is what the cable companies do to the signal before they send it down the cable!!! I thought at first I was disappointed with my new Panasonic Plasma because of the juddering image only to look carefully at the CRT in the other room to find the same issue but hadn't noticed it as this set is only 24" viewed from a distance rather than 42" viewed closer.
Ron Evans

[Dave Rosky]

Originally Posted by Aaron Courtney

Looks pretty good Dave. I'll only add that, as some people have found out with the Sony Bravia's in particular, that you have to turn OFF the 120Hz smooth motion in order for the display to natively process 24P material, which obviously is quite illogical, LOL.

That is kind of weird. I thought the main advantage of 120Hz is that since it is a multiple of both 24 and 30, it can display both 24P, 30P, and deinterlaced 60i (and of course even true 60P if there is ever source material) all using simple frame duplicating pulldowns like 4:4, 5:5, etc. That way, TVs can be built with only one referesh rate (120Hz), reducing cost and complexity. It sounds like Sony is using 120Hz to do something different like get smoother motion by interpolating frames. I haven't seen that set yet personally.

What would be absolutely ideal (outside of the stupid BDA revisiting its spec to reflect current trends in videography), is if every progressive display had the intelligence in its video processing chipset to natively process every conceivable format.

That would be a really good idea. Like you said, I think the TV is the correct place for this, since it is the end of the display chain and has control over its referesh rate. I'm not sure, but I think the Pioneer Kuro comes close. I believe (that is, I have heard) that it can recognize 2:3 pulldown and do the inverse telecine and display it as 3:3 at 72Hz. I don't know if it can take direct 24P and 30P, but if it can, it would be a pretty universal display device (it might well support those given your comment about 1080/30P in the broadcast standard). Unfortunately, though, as long as there are also dumber (and cheaper) sets out there, DVD and BD players will still have to have the capability to do some of the processing.

[Aaron Courtney]

Ron, I think we have to trust the broadcasters when they claim 720/60P and hope they maintain that progressive image through their entire chain. Perhaps you're seeing compression artifacts on the larger set. I have both an interlaced HDTV (Sony 34XBR970) and a PDP (Sammy 50"). Of course, everything looks better on the 34" Sony compared to the plasma, partly because CRT's are just plain better at everything beyond logistics, LOL, but also because the compression artifacts inherent in broadcast television are much less noticeable because of the size difference, even if I'm sitting <6ft from the TV.

Dave, I have never heard the 120Hz feature referencing 30P video. It's always been in relation to 24P and 60i material. The little trick about turning OFF the motion feature I discovered while reading a professional review of the LCD. Also, other reviewers and owners have confirmed it. And of course, it came up while discussing native support for 24P film material, not 30P video.

Of all the 120Hz capable displays, Samsung, if memory serves me, had the most horrifically convoluted way of handling 24P. I think the display first telecined and interlaced 24P to get to 60i, then de-interlaced, and then frame quadrupled to get to 120Hz, or something along those lines. What a joke! Whatever it was, in the end you essentially lost support for the whole 24P (sans pulldown) native thing anyway. You just shake your head and wonder what these companies are thinking!?

It truly is caveat emptor today in CE.

[Aaron Courtney]

Originally Posted by Dave Rosky

Unfortunately, though, as long as there are also dumber (and cheaper) sets out there, DVD and BD players will still have to have the capability to do some of the processing.

On the surface, this is no big deal, right? But the more you think about this and how you plan on connecting your AVR to your BD player in order to take advantage of the new lossless codecs (DTS-MA, Dolby Digital True HD) - using HDMI only option right? - then both the AVR and the display (via EDID) must be capable of accepting the BD player's output, otherwise, you'll have to revert to the most common denominator between the AVR and the display, which will likely not be the preferred selection/format.

See, the deeper you dig into this whole format mess, the more things start to unravel and the more chaos the end user is left to deal with because of the shortsightedness of CE manufacturers.

[Sean James]

Originally Posted by Dave Rosky

I didn't find a single place with a clear explanation of everything, but after looking around a lot, here is a really terse summary of the basics:

- Most newer TV's are progressive with a 60Hz referesh rate.

- A few TV's (e.g., Pioneer Kuro, but I can't guarantee that) have a few additional refresh rates that help with smoother (i.e., non-pulldown) display of 24P. These are usually either 72Hz or 96Hz, which are multiples of 24.

- A very few (maybe none at this point) can refresh at 120Hz, which is sort of a magic number because it is a multiple of both 24 and 30.

- A TV that refreshes at 60 Hz will deinterlace 60i material, and then display each deinterlaced frame twice in a row to get the 60Hz refresh rate. This is why on most progressive TV's, unlike older CRT's, 60i material doesn't necessarily have smoother motion than 30P

- A TV that can only refresh at 60Hz can only play 24P that has been pulled down to 60i, which normally happens in the DVD player. 2 out of every 5 frames will be interlaced in a way that contains a field from one 24P frame and a field from another 24P frame, so they don't necessarily deinterlace well, which is why such material won't look as good as 24P material on a TV that can change its refresh rate and display 24P with a "pure" pulldown like 3:3 or 4:4.

I'm a newbie to this too, so anyone please correct me if I'm wrong about any of this - I'd love to know so I can understand it more fully.

Thanks for this.

That means that if you want to play 24p on a modern, progressive TV, it would be reformatted twice, one 24p to 60i, and then to 60Hz(is that like 60p?).

It also looks like 60i is pretty much over.

So what about 30p footage on a 60Hz display? Should be OK, or not?

[Sean James]

Originally Posted by Aaron Courtney

What would be absolutely ideal (outside of the stupid BDA revisiting its spec to reflect current trends in videography), is if every progressive display had the intelligence in its video processing chipset to natively process every conceivable format.

If Blu-Ray doesn't do that, we may see another format coming, or not?

I have read a few comments on computer forums, that go into that direction: Blu-Ray has won - for NOW.

[Brian Boyko]

From the filmmaker's perspective, I'd say that you probably want to shoot at 30p instead of 60i in 95% of all situations, including NTSC television playback. 30p is a standard that gives you the nice, clear look of progressive video with a framerate that handles motion better than 24p.

Additionally, 30p converts to 60i very, very easily, and I don't think there would be much problem with interlacing the footage for broadcast.

And finally, what comes across as "motion blur" in 30p is exactly the same stuff that comes across as "interlacing artifacts" in 60i. That is, if you're moving the camera too fast to capture the subject within 1/30th of a second, you'll get interlacing lines in 60i (as the subject will have switched position in that fraction of a second)

But what about that other 5%? Well, in a word: Sports. If you absolutely know there is going to be fast action - split second action - you are going to want to get as many frames as possible in that 1 second; even if it means you're really only using half the resolution. 60i also does slow motion better than 30p - though you lose vertical resolution by "deinterlacing" the picture, you can get 60 "blended" frames with 60i, and slow that down to as low as 1/4 the speed before people start complaining about it being a slideshow.

So, why 24p?

The advantages of 24p are threefold: It gives you a "film-like" look that can look more professional if you do it right. This introduces motion blur that gives the video an... air of 'unreality.' And while you do have to deal with motion blur, you do NOT have to deal with interlacing problems, which look ugly. Motion blur - from time to time - can look elegant. Just try not to use it for handheld shots. In fact, 24p should probably almost always be on a tripod or dolly.

Additionally, 24p converts to 25p, and from there to 50i, more easily than 60i. This is important when considering a release in PAL country television, and it's one of the reasons I chose to film my documentary about NZ's politics in 24p. A 4% speedup (barely noticeable) and it's a conversion that takes care of itself.

Finally, if you hope for a theatrical release, 24p transfers to 16mm or 35mm film easily.

Now, there's no such thing as a wrong choice and there are ways to get the 24p look from 60i footage with ~$200 computer programs.

[Aaron Courtney]

Originally Posted by Sean James

Thanks for this.

That means that if you want to play 24p on a modern, progressive TV, it would be reformatted twice, one 24p to 60i, and then to 60Hz(is that like 60p?).

Not quite. The ideal method would be as we have already discussed. The BD film is authored as 1080/24P, the player recognizes 24P and passes it natively via HDMI to the progressive display which also recognizes 24P and merely frame triples (72Hz), quadruples (96Hz) or quintuples (120Hz) the original progressive frame video stream. You have to get out of the 60Hz rate if you want to eliminate judder from pulldown. Natively handling 24P material means neither the player nor the display is interpolating frames. The display, in this case - as in all other cases that I've read - is simply flashing the same frame delivered to it via the BD player 3x, 4x, or 5x generally depending on the manufacturer's design.

It also looks like 60i is pretty much over.

Hardly. It's firmly embedded in both the ATSC spec and the industry (not consumer) chosen HDM technology.

So what about 30p footage on a 60Hz display? Should be OK, or not?

As I've said either in this thread or the the one in the HV20 forum, it's a total crapshoot at this point depending entirely on the video processing chipset in the BD player. It seems easy enough right? Well, it ain't panning out that way in practice as the professional testers are finding out. I think HQV makes a BD torture test disc that you can purchase to evaluate how your display chain will handle 1080/30P video flagged as 60i in both BD and HD-DVD (probably irrelevant now unfortunately). BTW, they also make the venerable Silicon Optix HQV Reon chipset that is pretty much the best out there today, and one which handles 1080/30P video on BD with aplomb.

[Sean James]

Originally Posted by Brian Boyko

From the filmmaker's perspective, I'd say that you probably want to shoot at 30p instead of 60i in 95% of all situations, including NTSC television playback. 30p is a standard that gives you the nice, clear look of progressive video with a framerate that handles motion better than 24p.

Additionally, 30p converts to 60i very, very easily, and I don't think there would be much problem with interlacing the footage for broadcast.

And finally, what comes across as "motion blur" in 30p is exactly the same stuff that comes across as "interlacing artifacts" in 60i. That is, if you're moving the camera too fast to capture the subject within 1/30th of a second, you'll get interlacing lines in 60i (as the subject will have switched position in that fraction of a second)

But what about that other 5%? Well, in a word: Sports. If you absolutely know there is going to be fast action - split second action - you are going to want to get as many frames as possible in that 1 second; even if it means you're really only using half the resolution. 60i also does slow motion better than 30p - though you lose vertical resolution by "deinterlacing" the picture, you can get 60 "blended" frames with 60i, and slow that down to as low as 1/4 the speed before people start complaining about it being a slideshow.

So, why 24p?

The advantages of 24p are threefold: It gives you a "film-like" look that can look more professional if you do it right. This introduces motion blur that gives the video an... air of 'unreality.' And while you do have to deal with motion blur, you do NOT have to deal with interlacing problems, which look ugly. Motion blur - from time to time - can look elegant. Just try not to use it for handheld shots. In fact, 24p should probably almost always be on a tripod or dolly.

Additionally, 24p converts to 25p, and from there to 50i, more easily than 60i. This is important when considering a release in PAL country television, and it's one of the reasons I chose to film my documentary about NZ's politics in 24p. A 4% speedup (barely noticeable) and it's a conversion that takes care of itself.

Finally, if you hope for a theatrical release, 24p transfers to 16mm or 35mm film easily.

Now, there's no such thing as a wrong choice and there are ways to get the 24p look from 60i footage with ~$200 computer programs.

24p is always mentioned as the "film look".

I just wonder if the p as progressive isn't more important than the 24.

I mean, the shorter exposure time seems to speak a lot in favor of 30p.

[Ron Evans]

Just found this reference to displays that manage 24p correctly and thought it was of interest in this thread.

http://forum.blu-ray.com/showthread.php?t=5155

Ron Evans

[Sean James]

Glad the best displays are among them: the Sony LCDs and the Panasonic Plasma's.

[Ken Ross]

Originally Posted by Sean James

It also looks like 60i is pretty much over.

Not even close. 60i will be around for a very very long time.