1080i and 1080p bandwidth

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TomAckroyd

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Topic # 21508 29-Apr-2008 14:20

I regularly see 1080i referred to as being inferior to 1080p. Ignoring arguments about whether interlaced pictures are "worse" or "better" based on the temporal/spatial resolution tradeoff, could a helpful person explain to me why, in a TV transmission context, 1080i needs less bandwidth than 1080p? I'm confused because PAL SD bandwidth is identical regardless of whether it's film or video being transmitted.

Assume frame rates are identical. Show your workings :-)

Cheers,
Tom

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Reply # 127054 29-Apr-2008 14:28

1080i50 is equivalent to 25 full frames (50 half frames)
1080p50 is 50 full frames

Hence most of the time 1080i will run at half the bandwidth of 1080p.

The fact is on BluRay they also support 1080p24 which is a film referesh rate. I don't know of any broadcasters that are showing material in this form, but it would probably need about the same bandwidth as 1080i50.

The freeview|HD broadcasters have for the moment decided not to implement resolution switching as part of their broadcasts so you won't be seeing 1080p24 here any time soon.

Generally known online as OpenMedia, now working for Red Hat New Zealand as a Solution Architect for all things Linux, Virtual and of course Cloud. Still playing with MythTV and digital media on the side.

TomAckroyd

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Reply # 127087 29-Apr-2008 16:00

I never realised people had anything other than 1080p24, 25 or 30 in mind when talking about TV. Blu-Ray and the big American dramas are all 1080p24.

Surely no-one's actually producing TV at 1080p50/60? Whenever you see 1080p mentioned in NZ - whether talking about BluRay or flat screen TVs - it's always 24 or 25. And TV3 are transmitting Lost etc on FreeviewHD as 1080p25 - correct?

So with no domestic displays capable of 1080p at a framerate greater than 30 is this discussion purely academic?

Tom

Fossie

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Reply # 127091 29-Apr-2008 16:16

Tv3 is 1080i and doesn't carry lost

cyril7

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Reply # 127095 29-Apr-2008 16:30

So with no domestic displays capable of 1080p at a framerate greater than 30 is this discussion purely academic?

Pretty much. As you may be aware 1080p24 (and 25) are common in production, but actually treated as 1080sF24 and as such really appear as 1080i to the recorders, switches, routers etc. The only real difference is the flaging of sF24 (or sF25) clearly pairs half frames of a common source 24/25p frame with in an interlace studio enviroment.

I guess the real issue is in the display enviroment where many newer top line displays support 24p as an input and display it as 72p and thus no interlace artifacts need be concidered, which are a real issue in the 60i world.

Cyril

TomAckroyd

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Reply # 127099 29-Apr-2008 16:34

Fossie - ta. So for TV3, the US content they are transmitting in HD would be supplied to them as a 108i50 tape?

I've no idea what's on what channel ...

openmedia

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Reply # 127100 29-Apr-2008 16:36

TV3 broadcast here is 1080i50 - ie 50 half frames.

TV's here can usually handle 1080p24, 1080i50/60 and 1080p50/60

The higher end Sony sets with Motion flow actually show 1080p24 at 120 frames a second showing each frame of film 5 times.

cyril7

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Reply # 127102 29-Apr-2008 16:41

Sony sets with Motion flow actually show 1080p24 at 120 frames

Quite right, but we get the idea :)

Cyril

TomAckroyd

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Reply # 127104 29-Apr-2008 16:43

cyril7:

So with no domestic displays capable of 1080p at a framerate greater than 30 is this discussion purely academic?

Pretty much. As you may be aware 1080p24 (and 25) are common in production, but actually treated as 1080sF24 and as such really appear as 1080i to the recorders, switches, routers etc. The only real difference is the flaging of sF24 (or sF25) clearly pairs half frames of a common source 24/25p frame with in an interlace studio enviroment.

I guess the real issue is in the display enviroment where many newer top line displays support 24p as an input and display it as 72p and thus no interlace artifacts need be concidered, which are a real issue in the 60i world.

Cyril

I'm beginning to understand now about segmented formatting - cheers Cyril.

Following Fossie's reply - so a US 1080p24-originated show would be mastered out to 3:2 segmented tape for domestic 1080i60 distribution, and similarly the master for "PAL" ie 50Hz territories would be put to tape as 1080sF25 for tx at 1080i50?

TomAckroyd

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Reply # 127106 29-Apr-2008 16:45

openmedia:TV's here can usually handle 1080p24, 1080i50/60 and 1080p50/60

Again - where on earth is anyone seeing 1080p50/60?

openmedia

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Reply # 127134 29-Apr-2008 18:05

TomAckroyd:
openmedia:TV's here can usually handle 1080p24, 1080i50/60 and 1080p50/60

Again - where on earth is anyone seeing 1080p50/60?

PS3 can display games at 1080p50/60, but it isn't used for broadcast.

TomAckroyd

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Reply # 127141 29-Apr-2008 19:01

Openmedia - I stand corrected.

richms

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Reply # 127566 1-May-2008 14:00

So with no domestic displays capable of 1080p at a framerate greater than 30 is this discussion purely academic?

Tom

Plenty can, PS3 uses it, computers use it. Looks a hell of a lot better then 1080i into a flatpanel.

Richard rich.ms

lchiu7

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Reply # 127781 2-May-2008 08:34

TomAckroyd: Fossie - ta. So for TV3, the US content they are transmitting in HD would be supplied to them as a 108i50 tape?

I've no idea what's on what channel ...

If they are shooting in HD then I suspect they are shooting in 1080/24. That makes it reasonably easy to convert to 1080/60 for the local market and send us (would it be speeded up?) 1080/50.

If they are originating on film (I have heard that folks still use Super16) then once again the telecine (or whatever they call film to digital transfers these days) would do the same thing. It's a pity that the DVB didn't also decided to standardise on 60Hz since the days where we had to rely on mains frequency for sync are way way gone.

Out of interest I must grab a copy of a local BD title for which I have the US version and see if there is a pitch difference

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TomAckroyd

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Reply # 127792 2-May-2008 08:56

Random thoughts:

Larry - see my earlier topic in this forum about sped-up audio

I look forward to the day when everything is 24p

For a while in the 80s some Canadian made-for-TV movies were shot on film at 30fps. Made for a smoother picture in NTSC.

For 24p-originated programmes I would prefer to watch sped-up 25fps than 3:2 pulldown anyday.

openmedia wrote: "The higher end Sony sets with Motion flow actually show 1080p24 at 120 frames a second showing each frame of film 5 times". I understand about 48Hz at the movies but this is ridiculous. Showing one frame 5 times in a row on an LCD panel is surely no different from showing it once for a 25th of a second. What's the downtime between frames on these displays anyway? If you were to film it at high speed would you ever see a black screen? I doubt it.

Also - PS3 at 50p must look pretty cool. If the engine actually renders each 50th of a second's motion. Does it?

openmedia

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Reply # 127819 2-May-2008 09:49

openmedia wrote: "The higher end Sony sets with Motion flow actually show 1080p24 at 120 frames a second showing each frame of film 5 times". I understand about 48Hz at the movies but this is ridiculous. Showing one frame 5 times in a row on an LCD panel is surely no different from showing it once for a 25th of a second. What's the downtime between frames on these displays anyway? If you were to film it at high speed would you ever see a black screen? I doubt it.

Well with Motion flow they actually interpolate some of these frames to try and create a smoother picture.

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