1080i worthwhile for LCD?

[Bluestraw]

Maybe I'm missing something, but will a 1080i transmission always look worse on a LCD with native 720p resolution? The extra pixels are surely 'lost', and so the lower frame rate is the only difference.

Or is there more to it than this ?! Thanks in advance - I'm learning here!

[AML]

I think if the source is say 720p then yes, there would be some downscaling. But even so it would look good. I dont know about frame rate. I really REALLY doubt you would be able to see any difference.

Its not like we are all going to have 2 different panels, One for 720p material and one for 1080i material!
You also have to consider future material being in 1080p which means its prbably best to invest in a 1080p screen.

I think people are looking way to much into this whole hidef business.

Even a 1024X1024 panels looks darn good so I wouldnt worry too much if the screen is either 1280X720 or 1920X1080.
Just becuase a majority of material will be in 720p doesnt mean you HAVE to get a 1280X720 screen to watch it on.

[joker_zero]

Depends on the panel. 1080i scales quite nicely to 720p (1:1.5), also 1080i is only really 30Hz for the complete image, 720p on anything upto about 42" should look a little better.

This whole concept assumes that quality is directly related to the amount of data put on the screen in a given time.

So to use some crude math, in 1 second:
540i delivers 16,200 lines to the screen
540p delivers 32,400 lines to the screen

720p delivers 43,200 lines to the screen
1080p delivers 64,800 lines to the screen

1080i only delivers 32,400 lines to the screen THE SAME AS 540P

So for a given resolution 720p carries 33% more data to the screen in a given time period than 1080i.

Image processing tricks and other details such as the fact that the resolutions quoted for the transmissions only relate to luminescence and not the colour channels are all factors, but the bottom line is that right now nothing is being filmed in 1080p. So the 'best' we can hope for is 1080i, and 1080i from at least one perspective is not as good as 720p.

[joker_zero]

To be crystal clear before anyone flames this the above assumes a consistent horizontal resoultion - which is not the case and the increase in horizontal res of 1080i to 1920 will of course put way more data on the screen than a 4:3 or 16:9 540p image.

[DanDT]

Originally Posted by joker_zero

Depends on the panel. 1080i scales quite nicely to 720p (1:1.5), also 1080i is only really 30Hz for the complete image, 720p on anything upto about 42" should look a little better.

So for a given resolution 720p carries 33% more data to the screen in a given time period than 1080i.

But 1080i has effectively 2M pixels (1920x1080), though displayed in an interlaced manner. That's double the pixels compared to 720p, which has 1M pixels (1280x720).

So, double the pixel resolution for pretty much the same bandwidth sounds pretty cool to me.

Obviously 720p suits some programs better than 1080i and vice versa.

[joker_zero]

Not over a fixed period of time this is not the same as res
in 1 second:
1080i * 1920 *30 = 62,208,00 pixels displayed.
720p * 1268 *60 = 54,777,600 pixels displayed.

So overall 1080i carries only 12% more data than 720p

1080p is a different story - 44% more than 720p.

[Stephen Neal]

Originally Posted by DanDT

But 1080i has effectively 2M pixels (1920x1080), though displayed in an interlaced manner. That's double the pixels compared to 720p, which has 1M pixels (1280x720).

So, double the pixel resolution for pretty much the same bandwidth sounds pretty cool to me.

Obviously 720p suits some programs better than 1080i and vice versa.

Ah - but don't forget about interlacing and vertical pre-filtering.

A 1080i video signal may have 1080 lines vertically - split into 2 fields of 540 lines - but this doesn't mean it delivers 1080 lines of vertical resolution, even on static information.

This is because interlaced video sources from video cameras, telecines etc. are filtered vertically to around the 800 line resolution level, to avoid the objectionable flicker you get on fine vertical detail on an interlaced screen. If you imagine fine vertical detail presented in an interlaced manner, you'd get flicker at the frame rate 25 or 30 Hz) rather than at the field rate (50 or 60 Hz)

This vertical resolution obviously drops to 540 lines or a little below on fast moving scenes because the 1080/50i system acts like a 540/50p system on such sources.

You also have to consider vertical movement in interlaced systems - as some speeds of vertical motion are indistinguishable from fine vertical resolution - another reason for vertically pre-filtering.

Of course horizontally the case is different, and the 1920 horizontal samples ARE more comparable with those of a 1280 based system irrespective of interlace vs progressive.

[Stephen Neal]

Originally Posted by joker_zero

Not over a fixed period of time this is not the same as res
in 1 second:
1080i * 1920 *30 = 62,208,00 pixels displayed.
720p * 1268 *60 = 54,777,600 pixels displayed.

So overall 1080i carries only 12% more data than 720p

1080p is a different story - 44% more than 720p.

Yes - interlacing confuses a LOT of people.

I find it helpful to think in best and worse case scenarios :

On static/slow moving information, and film sources, a 1080i system acts a bit like a 1920x800/25p system. (800 is approx the vertical resolution delivered by a pre-filtered 1080i system)

On faster moving information a 1080i system acts a bit like a 1920x540/50p system.

In all cases a 1280x720/50p system acts like a 1280x720/50p system.

[Bluestraw]

Wow! Thanks for the detailed technical explanations there. To be honest, maybe somewhat above my understanding, but I think I get it...

One thing I'm still not 100% clear. I know people say that 'some programmes are better for 1080i, and some for 720p' (films vs sports for example). Am I right in thinking that, if I'm viewing on a LCD panel with native 1366x768 resolution, then I will not notice any 'improvement' of resolution for 1080i vs 720p? All I will get is a halved frame rate, which isn't too important since film is only shot at 24fps anyway...

Thanks!

[DanDT]

Originally Posted by Bluestraw

Wow! Thanks for the detailed technical explanations there. To be honest, maybe somewhat above my understanding, but I think I get it...

One thing I'm still not 100% clear. I know people say that 'some programmes are better for 1080i, and some for 720p' (films vs sports for example). Am I right in thinking that, if I'm viewing on a LCD panel with native 1366x768 resolution, then I will not notice any 'improvement' of resolution for 1080i vs 720p? All I will get is a halved frame rate, which isn't too important since film is only shot at 24fps anyway...

Thanks!

Well ultimately, if you watch on a 1366x768 LCD screen, the screen will scale the image to its native resolution, so if you're sending a 1080i signal, it will be scaled down to 720p (or whatever strange resolutions LCD screens go by today).
I think we'll have to wait for 1080p/i screen to see the difference between 1080i and 720p, because only 1920x1080 screens (1080p/i) will also be able to show a proper 1080i image, as well as anything below that.
A bit confusing i know.

[joker_zero]

dead right, the interesting aside is 'how is a 720p image constructed from a 1080i one over time?

Its easy to see 1080i divides by 1.5 to lose enough lines to become 720i but thats throwing valuable image data away that you can use to push that refresh frequency up toward 60Hz.

But what piece of magic takes 2 fields of 540 lines delivered at a net of 30Hz and turns this into one field of 720 lines delivered at 60Hz? Its the quality of the algorythm and its processing to take best advantage of the data available to make the best possible image.

Can the clever boys and girls in Japan make a better 1 second of animated live TV squishing 1080i30 into 720p60 or will the 1080i 30 image always be better?

I think it depends on lots of factors but as you say, until we get 1080 panels we wont know.

What really p1sses me off is that the USA are gettign true 1080 panels right now for under £1500, while we have to fork out 2K for a decent 768 jobby - once again rip-off Britain is the policy from Sony-san and Sharp dressed man.

[neilmcl]

Originally Posted by joker_zero

What really p1sses me off is that the USA are gettign true 1080 panels right now for under £1500, while we have to fork out 2K for a decent 768 jobby - once again rip-off Britain is the policy from Sony-san and Sharp dressed man.

I don't understand why people here are so upset about not able to get their hands on these 1080 panels at the moment. So what, lets face it, there's nothing to watch on them yet if you could get one and by the time there's a proper selection of HD material to view and play with them then hopefully the prices and availabilty of these TVs will be a lot better. Patience people please

[joker_zero]

That’s Easy
Sony PS3 specified to support 1080p

Sky HD specified as 1080i for most stuff, NOT 720p

only source for 720p now are PC's and 'upscaled DVD' both of which also support 1080

Xbox 360 is 720p and that’s it -

So what I don’t understand is why manufacturers assume we only need 768 line panels.

What astounds me is people cheerfully paying 50-100% more for a lower resolution than we should be getting.

[neilmcl]

Originally Posted by joker_zero

That’s Easy
Sony PS3 specified to support 1080p

Sky HD specified as 1080i for most stuff, NOT 720p

only source for 720p now are PC's and 'upscaled DVD' both of which also support 1080

Xbox 360 is 720p and that’s it -

So what I don’t understand is why manufacturers assume we only need 768 line panels.

What astounds me is people cheerfully paying 50-100% more for a lower resolution than we should be getting.

That's my point Sky HD and to a lesser extent PS3 are months away so why not wait it out until we get a full offereing before trying to get hold of 1080p panels. And when I say full offering I mean not just half a dozen channels and few games but the majority of output which will be some way off yet.

Also I don't think Sky have specified there preference of 1080i over 720p.

[NackNack]

I remember them saying that people would prefer 1080i more, so they're primarily going down that route,.