LCD TV's 42inch/46inch

[feo]

That I still can't figure out ... I don't understand the method on how they get 540 lines to fill 768 ... but the same thing applies to the 720p ... because they need to fill a display of 768 lines with 720 lines ... which is the same sort of concept. Also ... I'm not sure what a standard TV signal is ... I think it is 480 lines ... but what ever the number ... they also have to get that to fill 768 lines ... so in all these cases they have to get it to fill somehow.

Well, on a standard TV image 480 (I think), isn't inter/extrapolation used to stretch the image to fit the screen? It looks better on some TVs because different TVs have different ways of stretching the image.

I don't think that they fill 720 lines with the 540 lines from the first pass. How can they? The 540 lines is only half the picture.

 

[feo]

You are still missing the point ... 1080i is not true high definition ... in essence its an optical illusion. It gives you the illusion of 1080 lines ... but in essence is only 2 x 540 lines ... i.e. 540 lines. Therefore the TV actually has to upscale it ti fit 768 lines ... but I'm not sure how the ratios work.

But it's 1080 DIFFERENT lines that it's using to make up the picture, it's just displaying them 540 at a time.

 

[Perdition]

Ok lets make this simple, don't think in terms of i or p, at the end of the day 1080 = 1080 horizontal lines in the final image. What happens on a 720p set is the 1080 image is DOWNSCALED to 768, not upscaled from 540 to 768.

 

[feo]

Ok lets make this simple, don't think in terms of i or p, at the end of the day 1080 = 1080 horizontal lines in the final image. What happens on a 720p set is the 1080 image is DOWNSCALED to 768, not upscaled from 540 to 768.

Thank you. That's exactly what I'm saying, downscaling happens and not upscaling.

 

[xrapidx]

oh...i knew that in this case at least...

 

[noxibox]

Yes ... with the 768p you are right, I just said that 720p is better than 1080i ... but I you are wrong with the resolution needed for 1080i.

To show 1080 whether interlaced or progressive you need 1080 lines.

If you needed a resolution of 1080 lcd to run 1080i ... why the hell would they have brought out 1080p which would then be an identical resolution.

Because progressive is better than interlaced.

 

[eitai2001]

But if its 1080 different lines being displayed 540 at a time ... then surely a TV which can handle 768 lines at a time is more than adequate.

Think of it this way ... you have 1000 apples. Your trolley can only fit in 600 at a time, but you like to break things down evenly ... so you take 500 of those apples, put them in the trolley drop them off, come back and fetch the other 500 apples. By the time you get to the drop off point the first 500 apples are gone, so you drop off the second 500. Now imagine this process happening so fast that the first lot of apples still appears in your head even though they're gone by the time the second lot of apples gets there.

 

[eitai2001]

To show 1080 whether interlaced or progressive you need 1080 lines.


Because progressive is better than interlaced.

So then why did they make interlaced if a TV needs to have 1080lines to show 1080i ... because then it wouldn't need to be interlaced as all the lines are already there?

 

[noxibox]

Interlaced means your trolley can hold 1000 apples, but you put in the first 500, then put in the second 500. You do this quickly enough that it appears that the trolley is holding 1000. The lines of the second field are not the same lines used by the first field. To show 1080i without downscaling you need 1080 lines.

 

[feo]

But if its 1080 different lines being displayed 540 at a time ... then surely a TV which can handle 768 lines at a time is more than adequate.

Absolutely not.

It's 1080 different, unique lines of resolution. In order to see the picture without any quality degradation you need to view it on a 1080 set, i or p doesn't matter. How are you gonna fit 1080 line of resolution onto only 768 lines without downscaling? Point is, it's not upscaling 540 to 720, it's downscaling 1080 to 720.

Think of it this way ... you have 1000 apples. Your trolley can only fit in 600 at a time, but you like to break things down evenly ... so you take 500 of those apples, put them in the trolley drop them off, come back and fetch the other 500 apples. By the time you get to the drop off point the first 500 apples are gone, so you drop off the second 500. Now imagine this process happening so fast that the first lot of apples still appears in your head even though they're gone by the time the second lot of apples gets there.

Well, actually what happens is that the apples are (magically) squashed to fit into the trolley all at once and all of them are dropped off at one time, 2 trips are not needed.

 

[eitai2001]

Who could we ask that is not from this forum that can give us an expert opinion. I think I will e-mail my manager at work who has been working with TV's for over 10 years ... and has been to worldwide events to view launches of new technologies ... and saw HD when it was still brand new before it hit the shelves overseas. He's in good speed with the big boys at LG, Samsung, Sony and Pioneer ... and has attended more training courses than a doctor studying a PhD ... will you guys be happy with his source ... it may come out that I am wrong.

 

[noxibox]

So then why did they make interlaced if a TV needs to have 1080lines to show 1080i ... because then it wouldn't need to be interlaced as all the lines are already there?

On an analogue TV it was easier to scan half frames, that is why PAL is 576i and NTSC is 480i.

720p sets seem to accept 1080i input. Presumably they're just not fast enough or perhaps their buffers are too small to accept and downscale 1080p to 720p so they can only accept 1080 lines in two halves.

 

[feo]

Who could we ask that is not from this forum that can give us an expert opinion. I think I will e-mail my manager at work who has been working with TV's for over 10 years ... and has been to worldwide events to view launches of new technologies ... and saw HD when it was still brand new before it hit the shelves overseas. He's in good speed with the big boys at LG, Samsung, Sony and Pioneer ... and has attended more training courses than a doctor studying a PhD ... will you guys be happy with his source ... it may come out that I am wrong.

TivoZA is definitely the man to answer this. He comes here quite a bit, only a matter of time before he sees this thread.

 

[eitai2001]

Interlaced means your trolley can hold 1000 apples, but you put in the first 500, then put in the second 500. You do this quickly enough that it appears that the trolley is holding 1000. The lines of the second field are not the same lines used by the first field. To show 1080i without downscaling you need 1080 lines.

But if you have the capability to fill the trolley with 1000 apples ... why didn't you in the first place ... and why has 1080i been out for so long, when 1080p TV's are a new thing.
If they had the capacity to fill the trolley with 1000 apples from the start, why did they bother interlacing it in the first place?

 

[noxibox]

Well, actually what happens is that the apples are (magically) squashed to fit into the trolley all at once and all of them are dropped off at one time, 2 trips are not needed.

With analogue TV you are putting them on the trolley in two passes. They stay on the trolley long enough that it produces the illusion that you did it in one pass.

 

[feo]

With analogue TV you are putting them on the trolley in two passes. They stay on the trolley long enough that it produces the illusion that you did it in one pass.

So when they say 1080i is downscaled to 720p, they mean it's actually 720i then?

We need TivoZA to explain what exactly happens when an interlaced picture is scaled to to a lower res progressive picture.

 

[noxibox]

But if you have the capability to fill the trolley with 1000 apples ... why didn't you in the first place ... and why has 1080i been out for so long, when 1080p TV's are a new thing.
If they had the capacity to fill the trolley with 1000 apples from the start, why did they bother interlacing it in the first place?

When it comes to digital TV where you have individually addressable pixels you would simply show the 1080 lines progressively if you have 1080 physical lines. 720p displays are downscaling the 1080 line input and there is obviously some limitation that prevents them from downscaling 1080p input. Support for 1080i would therefore have existed since the advent of lower resolution displays capable of downscaling the 1080 line interlaced input. 1080p support would have only become available when displays had 1080 addressable lines and therefore require no downscaling.

Analogue TV was different and they had good reasons for choosing to go with an interlaced display. I have a vague recollection of it having to do with the vertical scan rate achievable at a reasonable price, but I'd have to pull out my books on television. Interlacing allows you to mask flicker at a lower scan rate.

 

[eitai2001]

With analogue TV you are putting them on the trolley in two passes. They stay on the trolley long enough that it produces the illusion that you did it in one pass.

Thats my point ... but there is no downscalling involved because the tv can handle the 540 lines at a time ... the same as the trolley could accommodate 500 apples at a time ... and the trolley comes back for the second load so quickly it appears that all the apples are on the trolley as an optical illusion.

 

[noxibox]

So when they say 1080i is downscaled to 720p, they mean it's actually 720i then?

Not necessarily - presumably the data is placed somewhere just before going to the screen and that area would be able to hold 720 lines. The display's processing hardware can probably also only hold 720 lines, so it would take 540 lines, convert them to 360, place those in some final buffer, do the same with the second batch of 540 lines, then when it has 720 send them to the screen. That is what I'd expect. If the display's scaling hardware could store and manipulate 1080 lines before placing them in a final 720 line buffer, then I'd expect it to handle 1080p as well, but all the 720p displays I've seen only accept 1080i.

 

[eitai2001]

What you just said about the 540 down to 360 then eventually sending out 720 makes sense to me as well as my own theory ... but I'll get my manager to confirm how it works.