how many frames per second on a TV?

[gtskater]

you've got a standard UK, PAL television used to recieving the BBC at 50hz, which AFAIK, means 50 times a second - am I correct?

50hz translates to 25 frames per second, yeah?

and accordingly, 60hz translates to 30 frames per second, yeah?

so, when you've got developers boasting that something runs at 30 (or however many) frames per second, how does that work?

please explain to me how you get 30fps on say PGR2 on a standard, UK, PAL TV?

Is it something to do with displaying each frame twice on TV broadcasts?

[Papercut]

50hz translates to 25 frames per second, yeah?

and accordingly, 60hz translates to 30 frames per second, yeah?

Thats right yeah. Each frame is split into two interlaced fields, so there are 50 updates per second (50Hz) but 25 frames per second pal.

so, when you've got developers boasting that something runs at 30 (or however many) frames per second, how does that work?

please explain to me how you get 30fps on say PGR2 on a standard, UK, PAL TV?

30 frames per second would be for a 60Hz refresh rate, so at 50Hz that would be 25 frames per second (but a higher resolution).

For games running at 60fps, you only get half of each frame displayed. However, each two fields are usually so similar, you don't really notice the difference. Slowly panning or scrolling something horizontally will give it away through, you can see one field displaced horizontally from the other.

Prog scan TVs (with a prog scan console) will give you true 50/60 fps, with the entire frame being redrawn in a single pass 50 or 60 times a second.

[Bassman]

It gets interesting when you watch a movie on a UK TV.

The normal frame rate of a film is 24 frames a second.

For PAL the frame rate is increased to 25 so that each frame of the movie is shown for 2 refreshes of the screen.

With NTSC the movie plays at is correct 24 frames a second. Each frame is shown two and a half times (which is of course impossible). On a still this is OK but on pans across rooms or countryside you see a slightly jerky effect due to this.

This is also why if you compare a UK DVD release of a movie and the same movie on an American DVD you will find that the American version is longer.

[shortround]

please explain to me how you get 30fps on say PGR2 on a standard, UK, PAL TV?

Is it something to do with displaying each frame twice on TV broadcasts?

what you have to remember is that the framerate of a videogame and the refresh rate of a tv are two separate things. a videogame could just as well have only 10fps but still run on a 50hz display. all that would happen is that each of the 10 frames would be shown 5 times each per second. it's only when you go above 25fps that things would become complicated for a 50hz display. this is why pal versions of games are slowed down to either 25fps (for 30fps games) or 50fps (for 60fps games).

what baffles me is why people go on about games running at 60fps, when 30fps is already perfectly adequate. if you had a 30fps game running on a 60hz progressive scan display, each frame would be shown for two refreshes each and the image would be perfectly acceptable (you wouldn't be able to detect any jerkiness in movement since it's too fast for the human eye). so why do programmers waste memory making games run at 60fps when there is no need?

bear in mind that that when you go to the cinema the projector is only running at 24fps. i mean, when was the last time you sat in the cinema and thought to yourself "ooh, that looks a bit jerky"?

[Papercut]

if you had a 30fps game running on a 60hz progressive scan display, each frame would be shown for two refreshes each and the image would be perfectly acceptable (you wouldn't be able to detect any jerkiness in movement since it's too fast for the human eye).

That isn't true, the jerkyness of 30fps is quite noticable when cornering in PGR2.

Those fine tuned by years of arcade games playing, and more recently games like F Zero GX, would almost certainly spot the difference.

[shortround]

after doing a quick google search it appears you are correct. i found this: http://amo.net/NT/02-21-01FPS.html which suggests we are even capable of detecting up to 200fps! bloody hell. it says the reason we don't see jerkiness at 24fps film is because of motion blur, although quite how that works i don't know