What is with the fixation on 60fps *or* 30fps with consoles?

[London Geezer]

But people are not watching 30fps rate in the broadcast. It is effectively 60fps, since each broadcasted frame contains two different frames that are displayed to the viewer separately.

No. Hz and fps are 2 different things.
That's the refresh rate of the TV and how the 60Hz interlaced system works.
The material runs at 30fps, meaning the recordings were made at 30fps (24fps for movies). The TV will then display those in an interlaced manner at 60Hz.

Like HD resolutions, 720p is a 60Hz signal, but the material you see from broadcasts is all 30fps material. Meaning the screen is refreshed 60 times per second but show each frame twice (although some new HDTVs like Philip's ones with PixelPlus 2 tech work some kind of interpolation in between those frames and normal broadcasts and DVD material seems to run at 60fps - the result is quite amazing, i'd buy one in a heartbeat if i had the money - you really have to see one of them side by side another normal HDTV running the same DVD to see the difference, it's quite amazing)
60fps games in fact look buttery smooth compared to fast-moving broadcasts, because they run at double the framerate.

I don't think there is any broadcaster in the world that sends 60fps signals.

 

[jimpo]

No. Hz and fps are 2 different things.
That's the refresh rate of the TV and how the 60Hz interlaced system works.
The material runs at 30fps, meaning the recordings were made at 30fps (24fps for movies). The TV will then display those in an interlaced manner at 60Hz.

Sure the recordings are 30fps. But that is not relevant for the user experience. User experiences effectively 60fps refresh rate.

Each frame contains both odd and even lines. Let's say recording has frames 1, 2, 3...29, 30 for one second. What viewer sees is 60 separate frames 1odd, 1even, 2odd, 2even....30odd, 30even. Frame 1odd is from a separate point of time than frame 1even. Going by your racing example, viewer sees the F1 car in 60 separate positions during one second.

What this means is that both 60fps refresh rate AND good motion blur are required for same experience of fluidity as viewing racing from TV broadcast. What many racing games offer, 30fps and no motion blur, is quite far from that.

 

[Shifty Geezer]

No, the car is viewed in 30 positions, just with alternating lines. Like looking through a Venetian Blind at a scene you say every other line. Then move the blind down one 'notch' and you see the other half of the scene, every other line, but its the same scene. Footage is recorded at 30 fps noninterlaced so the image isn't updated every 60th second. The picture shown for each alternating field is the same frame as the first field, just a different half of the same image.

 

[London Geezer]

Sure the recordings are 30fps. But that is not relevant for the user experience. User experiences effectively 60fps refresh rate.

Each frame contains both odd and even lines. Let's say recording has frames 1, 2, 3...29, 30 for one second. What viewer sees is 60 separate frames 1odd, 1even, 2odd, 2even....30odd, 30even. Frame 1odd is from a separate point of time than frame 1even. Going by your racing example, viewer sees the F1 car in 60 separate positions during one second.

What this means is that both 60fps refresh rate AND good motion blur are required for same experience of fluidity as viewing racing from TV broadcast. What many racing games offer, 30fps and no motion blur, is quite far from that.

Nope, my example explained that looking at broadcasts and DVDs (for example), we only see a car (or anything else) in a different position 30 times in one second. The screen just updates the image 60 times every second.

Another example, more extreme so it might be easier to grasp. Imagine displaying a picture on a TV. The picture is completely still, so the fps is 0. However, the screen still updates at 60Hz.
By contrast, a game like GT4 moves at 60fps, meaning that in one second you see 60 "movements" and the TV will display each different frame properly, mapping each frame to each screen refresh.

Broadcasts and DVDs (and any other recording, including future HDDVD/BluRay) runs at 30fps, so we will see 30 "movements" each second, on screen that update the image 60 times in a second.

The reason these recordings look smooth most of the time (not all the time, it gets evident when the action is very fast and when there are long pans over the scenery - LOTR for example) is because of what you mentioned, temporal motion blur. :smile:

 

[jimpo]

No, the car is viewed in 30 positions, just with alternating lines. Like looking through a Venetian Blind at a scene you say every other line. Then move the blind down one 'notch' and you see the other half of the scene, every other line, but its the same scene. Footage is recorded at 30 fps noninterlaced so the image isn't updated every 60th second. The picture shown for each alternating field is the same frame as the first field, just a different half of the same image.

No, you are incorrect. Look at one frame grabbed from interlaced broadcast, and you can see that odd and even lines are from different points of time.

 

[London Geezer]

No, you are incorrect. Look at one frame grabbed from interlaced broadcast, and you can see that odd and even lines are from different points of time.

That's just because of bad grabs. A deinterlacer must be used when grabbing interlaced broadcasts pictures, and no one bothers.

Trust us on this if you don't want to believe us, broadcasts all run at 30fps. Always have and will stay like that for a very long time.

 

[jimpo]

That's just because of bad grabs. A deinterlacer must be used when grabbing interlaced broadcasts pictures, and no one bothers.

Sheesh.

You can use deinterlacer, if you wish to hide the fact that odd and even lines are from separate points of time. We are talking about one broadcasted frame, and whether it contains samples from two point of time. For that you need a raw frame grab. And it will show you that the frame contains combined information from two frames in a separate point of time, evident from the interlacing artifacts in moving objects.

The whole reason for interlaced signal is to gain 60fps user experience with 30fps signal. If the signal would be recorded in 30fps, why would we have interlacing in the first place?

 

[London Geezer]

Can't believe you're actually arguing that broadcasts run at 60fps. Shifty and I both explained why this is just not true, why not google it so you can find "reputable" sources to say what we're saying?

 

[jimpo]

Can't believe you're actually arguing that broadcasts run at 60fps. Shifty and I both explained why this is just not true, why not google it so you can find "reputable" sources to say what we're saying?

You'd better believe it! I don't think you actually explained me anything. I have quite little motivation to google this, since I already know how interlacing works. I do some video editing as a hobby, and I see proof constantly with my own eyes.

Quick google, though:
http://www.videouniversity.com/interlace.htm

"Now, interlaced video helps to smooth out motion, especially slow motion, since we're refreshing the picture (half of it, anyway) 60 times per second instead of 30. But let's say that there's motion in your image. The odd field will show the image in one location, and the even field will show it 1/60 of a second later, at a slightly different position. This results in an image that's full of jaggies...a sort of horizontal "hairiness" to the edges of moving objects. If you don't have a sample image handy, grab a deck of cards. Cut the cards and shuffle them together, but don't even up the edges. Look at the deck end-on. That's what a still made from interlaced video can look like."

I'm sure there are better links to be found, but as I mentioned, I really don't see the point in wasting too much effort on this.

 

[Phil]

I'm with london-boy and shifty here: with one full frame, in the very first TV refresh, it displays all the odd lines of that frame. With the second refresh, it refreshes the even lines of that very frame. Naturally, the information of the odd and even line isn't the same because the coordinates are shifted. With the 3rd and 4th refresh of the TV, you'll get the information of the second full frame.

In other words, you need 2 refreshes to get the information of 1 full frame when the source is at 30 fullframes-per-second.

A game which has 60 fullframes-per-second is giving you a different picture with every refresh of the tv-screen: With one full frame of the game, with the very first TV refresh, you get the odd lines of that frame. With the second refresh of the TV, you'll get the even lines of the second fullframe of the game.

 

[London Geezer]

You seem to be confused over what 60Hz (interlaced) is and the fact that recordings are made at 30fps. We all know what 60Hz (interlaced) is, what you're saying is that broadcasts run at 60fps, which is just not true, will never be true whatever you say.

I explained the difference between Hertz and Frames Per Second in my previous post.

 

[Phil]

Dang, 3rd page. I think my reply might have been missed on the last page which should clarify the misunderstanding:

requote:

I'm with london-boy and shifty here: with one full frame, in the very first TV refresh, it displays all the odd lines of that frame. With the second refresh, it refreshes the even lines of that very frame. Naturally, the information of the odd and even line isn't the same because the coordinates are shifted. With the 3rd and 4th refresh of the TV, you'll get the information of the second full frame.

In other words, you need 2 refreshes to get the information of 1 full frame when the source is at 30 fullframes-per-second.

A game which has 60 fullframes-per-second is giving you a different picture with every refresh of the tv-screen: With one full frame of the game, with the very first TV refresh, you get the odd lines of that frame. With the second refresh of the TV, you'll get the even lines of the second fullframe of the game.

 

[jimpo]

Just out of curiosity - have you, Phil, london-boy, shifty, actually seen a frame grab of broadcasted signal (from, for example, racing - not a movie originally recorded at 24fps), with the mentioned interlacing artifacts? I think seeing one would help you understand this. This is not a matter of opinions to be decided on "I think..." - you can get conclusive proof by just looking at one frame of the broadcast.

 

[London Geezer]

Just out of curiosity - have you, Phil, london-boy, shifty, actually seen a frame grab of broadcasted signal (from, for example, racing - not a movie originally recorded at 24fps), with the mentioned interlacing artifacts? I think seeing one would help you understand this. This is not a matter of opinions to be decided on "I think..." - you can get conclusive proof by just looking at one frame of the broadcast.

You are wrong.

Broadcasts run at 30fps. End of story. Screen grabs have nothing to do with your opinion over this. And it's not an "opinion". You are wrong because you are wrong.

If you wanna keep thinking that you're watching F1 broadcasts at 60fps, keep thinking that, it seems you're not going to listen to us anyway.

I only spend time explaining things if people listen.

 

[London Geezer]

There are two Mains power frequencies widely used arround the World, 50Hz and 60Hz. This immediately divided the worlds TV systems into two distinct camps, the 25 frames per second camp (50Hz) and the 30 frames per second camp (60Hz).

http://www.ee.surrey.ac.uk/Contrib/WorldTV/why.html


Also:

http://www.shoots.com/worldstd.html

Anything else you need? you've been confusing fps with Hz from the beginning, i've explained why from the beginning, now will you believe more knowledgeable people than you (that's Shifty,Phil and I) after looking at those 2 links i provided?

 

[DrPetter]

I feel the need to pitch in here. Both jimpo and Phil are correct, but are addressing different issues. Broadcast content is indeed recorded at 60 Hz for NTSC and 50 Hz for PAL, and displayed interlaced in the form of even and odd lines.
This means it IS possible, with proper deinterlacing, to extract a true 30 fps (for NTSC) half speed slow-motion sequence from a broacast video capture, albeit at half the vertical resolution.
It is explained pretty well in images at the top of this page:
http://www.lurkertech.com/lg/fields/fields.html
I too speak from experience of hobby video editing.

 

[London Geezer]

I feel the need to pitch in here. Both jimpo and Phil are correct, but are addressing different issues. Broadcast content is indeed recorded at 60 Hz for NTSC and 50 Hz for PAL, and displayed interlaced in the form of even and odd lines.
This means it IS possible, with proper deinterlacing, to extract a true 30 fps (for NTSC) half speed slow-motion sequence from a broacast video capture, albeit at half the vertical resolution.
It is explained pretty well in images at the top of this page:
http://www.lurkertech.com/lg/fields/fields.html
I too speak from experience of hobby video editing.

Jim is basically saying that broadcasts (like the F1 example he provided) run at 60fps. That is not true and we proved why. They run at 60Hz/30fps.

But people are not watching 30fps rate in the broadcast. It is effectively 60fps, since each broadcasted frame contains two different frames that are displayed to the viewer separately.

 

[function]

In the same way that video games can use a different frame to generate every field (giving you 50/60 "fps" games) broadcast tv can generate its 50/60 fields from different frames. Fast moving scenes work a lot better this way than using 25/30 "full" frames.

 

[London Geezer]

In the same way that video games can use a different frame to generate every field (giving you 50/60 "fps" games) broadcast tv can generate its 50/60 fields from different frames. Fast moving scenes work a lot better this way than using 25/30 "full" frames.

I can't say i've ever heard of a broadcaster doing as such.

 

[DrPetter]

I'm sorry for writing Hz instead of fps in my last post, I view them as being the same thing since essentially they are. jimpo IS correct, they are broadcast at 60 frames per second, see the first four image sequences in my link.
Of course I can't pretend that I know exactly how F1 broadcasts work in your area, but all television content in Sweden is broadcast at 50 fps interlaced and that's a fact.