How can an ordinary TV display over 30 FPS?

[Tidus873]

OK, so an ordinary TV displays 60 interlaced fields per second (60 Hz) (NTSC) = 30 frames per second.For PAL it's 50 fields, 50 Hz, 25 frames.And I've been told some PS2 games run at 60 frames per second, how is that possible?

Please, someone explain!
I've been reading what not and still can't get it.I know I'm dumb, but...

[anephric]

Afaik, it's not, unless they're running in PAL60. If it's running in 50hz then 50fps is what you would get, optimised for full screen/"full" speed or no.

[Tidus873]

No, I don't mean how can PAL display over 50FPS, I know that FPS cannot exceed the refresh rate (50 Hz).What I'm asking is how can the fps be higher than 25/30 (PAL/NTSC)?

[anephric]

Well, with a progressive LCD or CRT, you'd get 60 true fields per second (assuming 480p etc), instead of half-fields (interlaced signals work by displaying every other line, rather than constructing a true full raster, so they're effectively half-resolution): on an interlaced display there's some field- or frame-mixing involved (I think) so you don't get 50 or 60 "true" frames a second being displayed on your TV: it would be 25 or 30, PAL or NTSC.

I think. I've got confused.

[Matt]

No, I don't mean how can PAL display over 50FPS, I know that FPS cannot exceed the refresh rate (50 Hz).What I'm asking is how can the fps be higher than 25/30 (PAL/NTSC)?

Here goes... fingers crossed...

The TV updates 50 times per second - 50 "half frames" or fields. PAL at 25 frames is two fields, the TV drawing first the odd and then the even lines (or the other way round, can't remember).

You seem pretty clear on the concept of fields already so that saves me making a **** up trying to explain it

If a game runs at 50 fps, all it's doing is updating each field with a unique image. If it's running at 25fps, the Even and Odd fields would be drawn from the same buffer image; if it's 50fps, the game updates the image so the Even and Odd fields are drawn from a different image different. It's rendering more times.

It's still only 25 full frames, but it's 50 fields and you shouldn't be able to see the interlaced image - however I think it's responsible for a lot of PS2's jaggies (??).

**** is any of this clear, it's been a long day?

I recall PGR2 was 25fps but the game ran internally, so to speak, at 50fps - that is to say it was sampling I/O, doing physics and AI 50 times per second, but only rendering 25 times.

I hope that's enough as I'm kind of making this up as I go along

[randombs]

yeah those twats at polyphony tried that stunt too with GT2 i think - that the game is running in 60fps internally but the video is at 30fps. it's a load of bollocks really

i was told that if a game is running in 50fps (or 60) then the telly is still showing all 50 frames, they're just split into two fields each (hence 100 half-frames)?

i mean, it can be done. the crt can be running at whatever frequency they want it to run at - just needs a crystal in there (how else would we be playing 60hz stuff)

[Tidus873]

The nightmare continues...
Damn, why can't I be one of those people that just push the power button and play and don't care about FPS, Hz, Progressive Scan and all that other stuff.

Sorry, Chain but I still don't get it.Thanks for trying anyway.

Let me try and rephrase my question:

let's put aside Progressive Scan for now.I will give an example with the game Devil May Cry 3 - this game doesn't support it.They say it runs on 60 FRAMES per second - that's 120 interlaced fields (1 full frame = 2 fields) and for an ordinary TV to display 120 fields in one second it has to have a frequency of 120 Hz and it has only 60 Hz.So... how?

i was told that if a game is running in 50fps (or 60) then the telly is still showing all 50 frames, they're just split into two fields each (hence 100 half-frames)?

i mean, it can be done. the crt can be running at whatever frequency they want it to run at - just needs a crystal in there (how else would we be playing 60hz stuff)

Hell then why do they label TVs 50 or 60 Hz

[sj33]

It's 60fps, with every other field being refreshed at any certain time. So each individual field would get refreshed 30 times per second, but the screen itself is still being refreshed at 60Hz. The end result is still a 60fps image, it's just the manner of refresh means that detail is lost (or rather, not being refreshed at full frame rate, but as the fields are).

It's complex, but it's still a 60fps result, even if the manner of refresh means it's somewhat crippled.

[randombs]

the fact of the matter is this:

on a normal telly (i.e. interlaced), 30fps looks jerkier than 60fps, therefore something IS happening faster, or else 60fps would just look like 30fps wouldn't it

the pal/ntsc 25/30fps frame rates are talking about television broadcasts.

[Psyduck]

Not sure if I'm going to help or hinder here - I know little about this, but I'll try to explain it as I understand it to see if it helps.
A frame is made up of two fields, and a (PAL 60) TV displays 60 fields per second. At 30fps it obviously displays the two fields of each frame one after another, making the 60 fields.
If a game is running at 60fps, it only displays one field of each frame, and they kinda blend together. This gives smoother movement but can cause "jaggies" because things have moved from one frame to another.

I think that should be easy enough to follow, just don't know if I'm actually right...

[andrewfee]

Simple - it's not 60fps. Assuming NTSC - if your game is running at 30fps, then being shown on an interlaced display it's "split" and sent as 60 fields and you see the same framerate. (half-frames) That one is easy.

If the game is running on the console at 60fps internally, that can only be shown progressively. (a 100Hz/120Hz TV isn't actually running any quicker, it's just doubling the fields sent to it) Everything is more responsive and more fluid, as controls etc are updated quicker, but you're not seeing any more frames. Now, I'm not sure how the output is done - whether it's 60 odd fields, 60 even fields, alternating fields (I don't think it's that though, or 60fps games would look like half the resolution) or some kind of blending (seems most likely) but you're only seeing 60 half-frames.

[Tidus873]

Not sure if I'm going to help or hinder here - I know little about this, but I'll try to explain it as I understand it to see if it helps.
A frame is made up of two fields, and a (PAL 60) TV displays 60 fields per second. At 30fps it obviously displays the two fields of each frame one after another, making the 60 fields.
If a game is running at 60fps, it only displays one field of each frame, and they kinda blend together. This gives smoother movement but can cause "jaggies" because things have moved from one frame to another.

I think that should be easy enough to follow, just don't know if I'm actually right...

^^Yeah, I considered that as an option, 'cause that kinda figures it out, but as you said the question is whether you're actually right.Because if that's the case you would only see half the resolution of the screen as andrewfee said.

Oh, well, I'll probably never figure that one out.

BTW, these forums turned up more active and responsive than I thought.And that's just great!

[Brats]

People get really mixed up with frames per second running on an interlaced screen. A 60fps game running on interlaced is not displaying at 30fps. This mistake often happens because interlaced is showing 'half' a frame each field and therefore people think 60fps displaying at half fields = 30fps. Also in TV two fields are often referred to as a frame, because TV runs at 30fps and therefore two fields really are a frame.

But games are different. As Billy says, 30fps looks clearly jerkier than 60fps even during cutscenes, so it is the image and not better reactions or any such toot.

The best way to think of it is this. In a progressive image, all scanlines are displayed in each of the 60 fields every second. A game running at 60fps will show every scan line for each frame, and every frame will be different.

Interlaced is the same except that less scan lines are displayed. Each field is still different from each other.

For example in a 60fps game like VF4, when field one is displayed the characters will be drawn on scanline 1,3,4,7 etc. In field two the character will have moved very slightly (it is not the same image as field one) and will be shwon on scanlines 2,4,6,8 etc.

[Psyduck]

following on from Brats, it's this different between lines 1,3,5,7 on the first field and then a slightly different image on lines 2,4,6,8 that creates "jaggies", because the two images shown together are slightly different - right? Hence prog scan, where each image is shown fully, looks better.

[anephric]

Ja, but a field isn't a frame, is it? And hence, since frame-mixing is going on you're not getting anything like true 60fps, but a bastardised frame-mixed version.