[leedsit]

Hi,

New to this AV stuff but just gota have a new HD TV... Pictures look amazing.. however I try to future proof all of my purchases so im thinking of purchasing a TV that supports 1900x1080, rather than the lower 720. Is this the right decision??? or is the difference between 720 / 1080 not that noticable???

Hi,

Most HD TV's support 1080i & 720p.

The basic difference is that for 720p, it displays 720 horizontal lines altogether, whereas 1080i displays 1080 horizontal lines as 2 screens of 540.

Basically...

A standard CRT tv displays all the odd numbered lines of a picture in one cycle, and then the even numbered lines. As this happens 50 times a second (assuming a 50Hz TV) the switch between displaying odd & even lines isn't noticable.
So a TV with 525 Horizontal lines could be classed as 525i.

I'm hard pushed to tell the difference between the two, but I'm no expert. The best thing is to get to a decent TV shop, and get them to show you the difference.

I'm sure someone on here will be able to give you a more technical answer...

[dan1979]

There is very little in the way of affordable 1080 displays out so there's not much of a decision really.

[redpavlos]

Suggest you make sure whatever you buy carries the 'HD Ready' logo.

To find out what that means, take a look here:
http://www.eicta.org/files/PressRelease1-114214A.pdf

Whatever the display format of the screen, the key point is that it should have HD capable inputs that accept the following HD video formats:

o 1280x720 @ 50 and 60Hz progressive (“720p”), and
o 1920x1080 @ 50 and 60Hz interlaced (“1080i”)

(also the 25 Hz / 30 Hz 'film mode' versions of 1080 progressive, the studio source data rates are same as for the 1080i versions)

This ensures that your screen will be capable of displaying all material that European broadcasters plan to use for HD transmissions, as well as what'll be on the new HD disk formats.

The differences subjectively between 720p and 1080i have been a matter of considerable debate in the professional production and broadcast communities, and there are those who hold strong views about both. 720p is better for fast motion such as football, while 1080i offers slightly higher resolution on non-moving parts of interlaced pictures, and is perhaps also optimum for film (in it's non-interlaced mode). 720p also has the advantage of requiring a lower bit rate than 1080i.

Many years before we'll see programmes transmitted anywhere in 1080p at 50 Hz and 60 Hz, which is what most people mean when they say '1080p'.

[DarkEntity]

Pioneer have a tv which supports 720, 1080i ans 1080p, but it costs a small house.

[leedsit]

Hi.

thanks for the replies.... I was looking at the philips 42Inch which supports 1920x1080i.... as you guys have said, these tv`s are more expensive ( about double the price of a HD tv that supports 720 ). However .... money aside... for watching normal HD Tv and HD Films ( upscaling DVD, Blueray or HD DVD ) if you had a 720 and a 1080 tv next to each other would the 1080 offer a much better picture than the 720 ( did the math and the 1080 does have 50% more horizontal lines )....

[Welwynnick]

Originally Posted by redpavlos

720p also has the advantage of requiring a lower bit rate than 1080i.

720p and 1080i both have the same pixel rate - 74.25 MHz. 720p has much longer blanking periods.

Nick

[redpavlos]

Originally Posted by leedsit

Hi.
.... money aside... for watching normal HD Tv and HD Films ( upscaling DVD, Blueray or HD DVD ) if you had a 720 and a 1080 tv next to each other would the 1080 offer a much better picture than the 720 ( did the math and the 1080 does have 50% more horizontal lines )....

The differences will depend on the format and quality of the source material, and the quality of the display and it's built-in scaler.

For 720p sources, at best, the 1080 TV would be no worse than the 720 one. For really good 1080i sources, the lower resolution of the 720p display is likely to be noticed only by those with good vision and a critical eye, and then only on really large displays - although it does also depend on the viewing distance. Surprising, but true from having seen such demos myself. The differences are not nearly as great as the numbers for theoretical resolution might suggest.

But in practice, i.e. in the real world where money cannot usually be ignored, you really need to look at various displays and picture sources for yourself, and not rely only on comparing paper specifications. This will hopefully be much easier to do over the coming year as HD sources become more readily available.

[redpavlos]

Originally Posted by welwynnick

720p and 1080i both have the same pixel rate - 74.25 MHz. 720p has much longer blanking periods.

Nick

In the digital studio environment, the uncompressed bit rate of both these signal formats is in practice carried over HD-SDI, at around 1.5 Gbit/s.

However, when compressed for transmission, using the progressive 720p format saves bit rate compared to 1080i. Whether MPEG-2, or MPEG-4.

[ianh64]

I don't think it really matters whether you go for 720p or 1080i. Until things get broadcast (read many many many years) in 1080p, its always going to be a compromise viewing 720p material upscaled on a 1080 screen or 1080 material downscaled on a 720 screen. I think watching 1080 material on a 720 screen is the better compromise at smaller screen sizes.

[SibTiger33]

Originally Posted by ianh64

I don't think it really matters whether you go for 720p or 1080i. Until things get broadcast (read many many many years) in 1080p, its always going to be a compromise viewing 720p material upscaled on a 1080 screen or 1080 material downscaled on a 720 screen. I think watching 1080 material on a 720 screen is the better compromise at smaller screen sizes.

excellent point


and by the time 1080 becomes more of the norm the prices of those sets should drop in price by alot and based on the knowledge of others and what i have seen myselve there really isnt a major diff between the two (well not enough of a diff to warrant the high price diff)

by the time 1080 becomes the norm ill be looking at SED screens by then anyway ;-) heheh

[lachesis]

*confused*

If I buy an HDTV which is 720p/1080i capable, and I am watching Sky Sports 1 which ?may? broadcast in 720p; if I switch to a movie channel which is 1080i (like Sky Movies 2) - will the TV switch between the two signals and adjust accordingly - or will it be a case of going into menus etc.

I appreciate I'm assuming a lot but theoretically is that the way it will work?

Upscaling and downscaling as well; what exactly does this mean? I am assuming on LCD that the res is 1024*768 and the 768 is scaled to 720 (same with 1080i)?

Thanks

[redpavlos]

Originally Posted by lachesis

*confused*

If I buy an HDTV which is 720p/1080i capable, and I am watching Sky Sports 1 which ?may? broadcast in 720p; if I switch to a movie channel which is 1080i (like Sky Movies 2) - will the TV switch between the two signals and adjust accordingly - or will it be a case of going into menus etc.

I appreciate I'm assuming a lot but theoretically is that the way it will work?

Upscaling and downscaling as well; what exactly does this mean? I am assuming on LCD that the res is 1024*768 and the 768 is scaled to 720 (same with 1080i)?

Thanks

An HD Ready display will switch automatically between 720p and 1080i. No need to go into any menus.

Basically, a 720p picture is made up of 1280x720 pixels, a 1080i one has 1920x1080 pixels.

Upscaling/downscaling simply means converting the signal delivered by your Sky box or DVD player etc to the format of your particular display (e.g. 1024x768). The display's electronic processing takes care of it all for you.

[Craig_E]

Originally Posted by leedsit

however I try to future proof all of my purchases

I'm not trolling here, but the minute I decided not to future-proof my decisions (AV related or otherwise) I was a happier person! Just get something cheap and cheerful now, and get something newer when something better comes along

As for 720p vs 1080i, not all people realise it takes the same amount of information for either resolution, but differently displayed. I would take progressive any day of the week.

But as we've seen in the Sky HD threads, I wouldn't worry about what your TV can do- it will always be able to do better than the mainsteam services. If I didn't have my laptop and Xbox 360, my HD plasma would have nothing of any decent resolution to display!

Bottom-line: say we get Sky HD this year, nothing new will come until 2012 when analogue is switched off, so if your current telly can do 720p, sit back and enjoy what HD material you can!

[lachesis]

Originally Posted by redpavlos

An HD Ready display will switch automatically between 720p and 1080i. No need to go into any menus.

Basically, a 720p picture is made up of 1280x720 pixels, a 1080i one has 1920x1080 pixels.

Upscaling/downscaling simply means converting the signal delivered by your Sky box or DVD player etc to the format of your particular display (e.g. 1024x768). The display's electronic processing takes care of it all for you.

Thanks for that info. I think I'm going to more than likely watch everything in 720p (I'll play my console in that signal and am assuming that Sports is also broadcast the same also).

I know a lot of people have said there isn't a lot of difference between 720p and 1080i in movies; would there be a way of making the 1080i movie channel auto downscale to 720p? Or is this totally not worth it? Assuming that the native res on the disaply is 768.

[redpavlos]

Originally Posted by lachesis

Thanks for that info. I think I'm going to more than likely watch everything in 720p (I'll play my console in that signal and am assuming that Sports is also broadcast the same also).

I know a lot of people have said there isn't a lot of difference between 720p and 1080i in movies; would there be a way of making the 1080i movie channel auto downscale to 720p? Or is this totally not worth it? Assuming that the native res on the disaply is 768.

Your display will in effect do this anyway, converting 1080i to its progressive native format. But when it comes to movies, there is a film mode variant of 1080i that is actually 1080 progressive at 25 Hz. This will be selected automatically. So no particular need to downcovert to 720p first, unless the scaler in the display doesn't perform well.

It might be that Sky HD boxes will offer the option of converting everything to give a 720p output - but I'm not sure. But downscaling from 1080i to 720p is in any case easier to do than upscaling from standard definition 576i to 720p.

I dare say it'll look very good on HD sources whether you feed your display with 720p or 1080i from the Sky box, and should certainly be visibly much better than feeding it standard definition.

[Stephen Neal]

Originally Posted by redpavlos

But downscaling from 1080i to 720p is in any case easier to do than upscaling from standard definition 576i to 720p.

Where did you get that idea from?

Many 720p displays don't downscale 1080i at all well as it is much more expensive to de-interlace 1080i than it is 576i. Many displays treat 1080i as 540p - whether it contains interlaced video material (i.e. 1080/50i native) or progressive film material in segmented-frame format (i.e. 1080/25p carried as 1080/50i). (In PC terms it only does a BOB de-interlace, and doesn't WEAVE for progressive material.)

This is cheap as it doesn't require any field motion detection or any form of adaptive de-interlacing. However it reduces the vertical resolution of the 1080i source to 540p, rather than the theoretical 800ish p it contains...

1080i de-interlacing to 1080p then scaling to 720p is the highest quality route for 1080i display on a 720/768 line display - but not all do this.

576i to 576p de-interlacing and then 576p to 720p scaling is easier and cheaper to do - as the source line/sample rate is much lower, and requires less processing power, though the 576 to 720 scaling requires a better vertical filter to do it well.

[redpavlos]

Originally Posted by Stephen Neal

Where did you get that idea from?

Many 720p displays don't downscale 1080i at all well as it is much more expensive to de-interlace 1080i than it is 576i. Many displays treat 1080i as 540p - whether it contains interlaced video material (i.e. 1080/50i native) or progressive film material in segmented-frame format (i.e. 1080/25p carried as 1080/50i). (In PC terms it only does a BOB de-interlace, and doesn't WEAVE for progressive material.)

This is cheap as it doesn't require any field motion detection or any form of adaptive de-interlacing. However it reduces the vertical resolution of the 1080i source to 540p, rather than the theoretical 800ish p it contains...

1080i de-interlacing to 1080p then scaling to 720p is the highest quality route for 1080i display on a 720/768 line display - but not all do this.

576i to 576p de-interlacing and then 576p to 720p scaling is easier and cheaper to do - as the source line/sample rate is much lower, and requires less processing power, though the 576 to 720 scaling requires a better vertical filter to do it well.

Ok, agreed if it's done properly. Hopefully not many current 1080 displays still treat 1080i in this way, but there may well still be some. Many early ones certainly opted for the then cheap solution.

But results on a 720/768p display should be generally better when starting with a higher resolution than upscaling from an interlaced lower one such as 576i.

Even better to stay progressive all the way from source to display.

The moral being you really need to see what it looks like for yourself and not rely on paper specs alone.

[Stephen Neal]

Originally Posted by redpavlos

Ok, agreed if it's done properly. Hopefully not many current 1080 displays still treat 1080i in this way, but there may well still be some. Many early ones certainly opted for the then cheap solution.

I thought we were talking about 720/768 displays - not 1080 ones? AIUI permanent 540p de-interlacing is still far-from-rare when providing 1080i input compatibility for sub-1080 line displays.

But results on a 720/768p display should be generally better when starting with a higher resolution than upscaling from an interlaced lower one such as 576i.

Absolutely - even permanent 540p will look better than the approx max 400p / min 288p that 576/50i effectively delivers.

However your original statement was that 1080i to 720/768p scaling was easier than 576/50i to 720/768p scaling I thought?

Whether 576/50i upscaled and 1080/50i downscaled LOOKS better is a different kettle of fish!

There are good and bad methods of handling 576/50i and 1080/50i - and this is key to the quality you get on a 720/768 display when fed with such sources.

Even better to stay progressive all the way from source to display.

In most cases - however 1080/50i carrying 1080/25p may not be that bad a compromise - and will almost certainly improve on 720/50p carrying 720/25p material.

Just as important will be the quality of the source material and the resulting compression, as well as the de-interlacing process.

It may well be that 1080/50i de-interlaced/scaled using a broadcast quality device by the broadcaster to 720/50p prior to transmission will look a lot better than 1080/50i broadcast as 1080/50i and converted to 720/50p by a cheap de-interlacer in the display.

The moral being you really need to see what it looks like for yourself and not rely on paper specs alone.

Absolutely - and it is vital to use real-world material in both SD and HD when making judgements, not just watch films on DVD and HD test loops.

Vital to watch material with 50i/50p motion - so many people just test SD performance with movie DVDs, which aren't at all demanding in many areas. (No real fast motion, no real adaptive de-interlacing etc.)