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The 720p vs 1080i question on ALIS 1024x1024


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#1 phreek

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Posted 13 August 2005 - 08:44 PM

Hi all,

Since getting the HD Fuji 42" I've been thinking of the 720p vs 1080i question. This is not to do with the merits of each format - that argument has been debated ad infinitum. My question relates to which of the two translates better to 1024x1024 ie. ALiS based Plasma screens like the Fuji and Hitachi (and Sony).

My personal eyeballing judgement is that 720p looks better on most broadcasts vs 1080i. I'm sure the reason has to do with the quality of broadcasting as much as anything.

Ultimately people say that 1080 lines is better than 720 regardless of interlacing. That's very simplistic.

On an ALiS screen one has a unique progressive display where half the lines are presented at one time (not like a CRT where the electron gun has to draw half the screen each cycle) instantaneously. The chief benefit is energy use is halved! A great benefit when considering power concerns.

Now to some maths. The incoming signals from a set top box are scaled by the panel to the 1024x1024 native resolution of the ALiS panel. With a 720p signal the scaling is thus:

Horizontal: 1280 ---> 1024 = 20% downscaling.
Vertical: 720 ---> 1024 = 42% upscaling.

With a 1080i signal it is:

Horizontal: 1920 ---> 1024 = 46% downscaling.
Vertical: 1080 ---> 1024 = 5% downscaling.

However we have to take into consideration that at each cycle the amount of information coming to the panel is different. With the 720p signal the panel is receiving 720 lines every cycle. By it's nature the ALiS panel uses all that 720 line information to light up only 512 lines (remember alternate)! So in fact it is not upscaling like one might think! Rather it's more like a 720 ---> 512 = 40% downscaling.

It's getting that 720 lines every cycle!

With a 1080i signal however it gets 540 lines per cycle. The math gives an identical 5% downscale when considered in relation to the 512 lines an ALiS panel displays each cycle.

Another important thing in these calculations is the RATIO between the scaling in each direction which can affect the efficiency and smooth appearance of image scaling. With the 720p signal the panel only has a ratio of at most about 2 to 1 between the horizontal and vertical axes. With the 1080i signal the ratio is 8 to 1!


A 1024x1024 ALiS is unable to diplay all the information in either a 1080i or 720p signal however these calculations above ought to indicate that the 720p signal is in fact superior to the 1080i for these particular panels.

It certainly matches up with my experience. The downscaling in 720p is confirmed when I look at the EPG menu of my LG 5100p box. On 720p output the menu is smaller onscreen than when a 1080i output is made.

I hope this helps decide which signal to use for 1024x1024 ALiS panels.

Regards,
Ben

#2 glenncol

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Posted 13 August 2005 - 08:46 PM

Dude grab a external scaler and scale everything to your native res then there is no worries.

#3 Foggy

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Posted 13 August 2005 - 09:04 PM

Very good summary and analysis phreek, but there's one minor flaw in your logic which would also partially explain why the EPG menu is smaller in 720P.

I believe that the scaler in AVMII (and the original AVM) truncates a small number of lines from the top and bottom of the 1080i picture to achieve a 1:1 vertical mapping.

#4 big_marcelo

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Posted 13 August 2005 - 09:32 PM

Very good summary and analysis phreek, but there's one minor flaw in your logic which would also partially explain why the EPG menu is smaller in 720P.

I believe that the scaler in AVMII (and the original AVM) truncates a small number of lines from the top and bottom of the 1080i picture to achieve a 1:1 vertical mapping.

<{POST_SNAPBACK}>

That's how the Hitachi does it ... would be nice if the FUij published more detailed information on its technolgy and processes..

Cheers,

Marcelo

#5 phreek

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Posted 13 August 2005 - 10:31 PM

It would be nice to know the methods the screen actually uses.

The calculations above show that the image is scaled 5% - a small amount vertically with the 1080i signal. The horizontal is 9 times more (I wrote 8 which was out by 1) which leads to a problem of proportionality.

Moreover if what I am conjecturing is correct - ie. more vertical information per cycle to make the 512 lines of an ALiS panel work then the 720p is actually giving a better picture just on that basis not to mention the better proportionality in the respective dimensions - a factor of 2; not 9.

I have just performed an A / B test using the 'Pelican Brief' being broadcast on 90 now. In 1080i mode the panel shows a fuzziness around the "HIGH DEFINITION" writing around the watermark.

In 720p mode the same writing is sharp as a pin and the whole image is more crisp.

Admittedly this could be due to the nature of the broadcast signal - my experience and conjecture shows that 720p is the way to go for a 1024x1024 native resolution.

#6 :)

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Posted 13 August 2005 - 10:33 PM

That's how the Hitachi does it ... would be nice if the FUij published more detailed information on its technolgy and processes..

Cheers,

Marcelo

<{POST_SNAPBACK}>


that is correct. the other fly in the ointment we aren't actually getting 1920x1080i infact only 1440x1080i at best in melb anyway not sure about else where in the country. Also john barber and championR in another thread confirmed that with the hd cameras used limitation is 1440x1080i(dues to tapes used) anyway and its scaled upto 1920x1080i even if we could get it.

phreek you might be interested in this post of mine that has a bit of detail on alis
http://www.dtvforum....ndpost&p=143636

re your post on 720p vs 1080 can't back you up there as really only seen 576p/i & 1080i on my alis hitachi

#7 phreek

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Posted 13 August 2005 - 10:45 PM

that is correct. the other fly in the ointment we aren't actually getting 1920x1080i infact only 1440x1080i at best in melb anyway not sure about else where in the country. Also john barber and championR in another thread confirmed that with the hd cameras used limitation is 1440x1080i(dues to tapes used) anyway and its scaled upto 1920x1080i even if we could get it.

phreek you might be interested in this post of mine that has a bit of detail on alis
http://www.dtvforum....ndpost&p=143636

re your post on 720p vs 1080 can't back you up there as really only seen 576p/i & 1080i on my alis hitachi

<{POST_SNAPBACK}>


Thanks alebonau,

Will read that asap.

It's important to remember that I am not talking about the merits of each format, nor the broadcast signal which is obviously going to affect the final quality.

What matters is the signal the STB is sending the panel for scaling. The STB receives the signal from its RF in and outputs it according to your selection. Its about the what is being fed into the panel and the calculations are based only on that rather than the broadcast signals format and quality which I agree is highly important.

I'm conjecturing and reporting that a 720p signal being fed from the STB is the way to optimise an ALiS 1024x1024 native resolution best.

#8 Foggy

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Posted 13 August 2005 - 10:50 PM

that is correct. the other fly in the ointment we aren't actually getting 1920x1080i infact only 1440x1080i at best in melb anyway not sure about else where in the country. Also john barber and championR in another thread confirmed that with the hd cameras used limitation is 1440x1080i(dues to tapes used) anyway and its scaled upto 1920x1080i even if we could get it.

<{POST_SNAPBACK}>

I initially thought the same thing al, but doesn't your STB actually upscale the 1440x1080i into 1920x1080i, or does the Australian DTV standard allow both?

#9 glenncol

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Posted 13 August 2005 - 11:03 PM

Very good summary and analysis phreek, but there's one minor flaw in your logic which would also partially explain why the EPG menu is smaller in 720P.

I believe that the scaler in AVMII (and the original AVM) truncates a small number of lines from the top and bottom of the 1080i picture to achieve a 1:1 vertical mapping.

<{POST_SNAPBACK}>


This will back up what you have said here

http://www.avsforum....S hd resolution

#10 Foggy

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Posted 13 August 2005 - 11:05 PM

All theory aside, I just did an A/B test and I still think that 1080i gives a slightly sharper image than 720P.

Maybe there's other factors at play that we haven't considered, some things that come to mind:
- colour rendering differences during the scaling process of interlaced vs progressive signals
- source feed. Maybe your LG STB does a better job with 720P output, whereas my AUSID prefers 1080i
- Differences in Calibration settings and Digital Processing features. You may have different menu options enabled that could behave differently with Progressive vs. interlaced signals

The difference is not that great, but on my setup, I still think 1080i is the better option.

#11 phreek

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Posted 13 August 2005 - 11:23 PM

All theory aside, I just did an A/B test and I still think that 1080i gives a slightly sharper image than 720P.

Maybe there's other factors at play that we haven't considered, some things that come to mind:
- colour rendering differences during the scaling process of interlaced vs progressive signals
- source feed. Maybe your LG STB does a better job with 720P output, whereas my AUSID prefers 1080i
- Differences in Calibration settings and Digital Processing features. You may have different menu options enabled that could behave differently with Progressive vs. interlaced signals

The difference is not that great, but on my setup, I still think 1080i is the better option.

<{POST_SNAPBACK}>


I've looked at the 720p vs 1080i signal on Bulletproof on 10HD (12) and again there's no doubt the 720p gives the sharper image. The 1080i is soft in comparison.

There is definitely a difference in the scaling between these two images. The position of the watermark is slightly different in each mode. In 720p the watermark is closer to the centre vertically, and closer to the edge in 1080i.

The STB is obviously a factor here and you may be right that it is the LG's peculiarity that this is so. It may also have to do with matching the source broadcast signal more closely with 720p input to the panel.

In any case the 720p signal is clearly sharper than the 1080i here.

#12 glenncol

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Posted 13 August 2005 - 11:34 PM

Post deleted

#13 :)

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Posted 13 August 2005 - 11:37 PM

I initially thought the same thing al, but doesn't your STB actually upscale the 1440x1080i into 1920x1080i, or does the Australian DTV standard allow both?

<{POST_SNAPBACK}>


I'm runnign the teac on auto mode foggy which has pass through of things as is to display, I'm not using upscaling via the stb.

#14 Champion_R

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Posted 14 August 2005 - 03:32 PM

Also john barber and championR in another thread confirmed that with the hd cameras used limitation is 1440x1080i(dues to tapes used) anyway and its scaled upto 1920x1080i even if we could get it.

<{POST_SNAPBACK}>

But keep in mind the end result has to be converted to 1920x1080 before display and the HDCam decks convert to 1920x1080 on playback. If the broadcaster provides 1440 then the tape is ~1440 then converted to 1920 then converted to 1440 for transmission and converted again to 1920 by your STB.

Better solution is for broadcasters to increase the HD bitrate and transmit 1920 then you have one conversion instead of three.

#15 phreek

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Posted 17 August 2005 - 09:30 PM

OK I've just done some testing on "House" running on 10HD (12).

I asked my wife to change the resolution on the box unknown to me 5 times, watching for 2 to 3 mins each time.

I preferred the 1080i input the 3 times it was presented.

I had played yesterday on XBox MC outputting 720p and 1080i formats and then checking framing of the image carefully and its absolutely correct that the ALiS panel is able to present the central 1024 lines - discarding 28 lines from the top and bottom and presenting the interlaced image natively.

Brilliant!

I know there's alot of debate about the merits and disadvantages of ALiS but this is really cool to get the 1:1 vertical resolution of 1080i. You can't help but love it if you're a fan :blink:.

The detractors always say that the interlaced image falls short compared to progressive but its all moot really. The technology works and works well. What did it for me is when I took a photo of the screen with a shutter speed faster than 1/60s. Now anyone who has photographed a CRT will know how it looks with half black screens etc.

I took digital photos of my ALiS panel at up to 1/1600s and believe it or not there is no half screen ie. odd line or even line on and other line off phenomenon. Every line even at these ridiculously short shutter speeds is lit!

It's technically still not a progressive screen, and the flicker is definitely visible when fed the right input ie. single horizontal white scanline surrounded by two black (off) but you don't see that on 'normal' inputs.

Anyhow 1080i is definitely the way to go!

Later.

#16 Owen

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Posted 17 August 2005 - 10:58 PM

Sounds like you are on a winner their dude.
The big test would be to look at a 1080 resolution test pattern to see if you are really getting full 1080 resolution. If it does, ALiS really does work.

Almost all digital displays use BOB deinterlacing on 1080i, which yields only 540p.
This is then upscaled to 768p or whatever the native panel resolution is.

If the AliS can display TRUE 1080i in interlaced form, it does not need to deinterlace, and should therefor have a very significant vertical resolution advantage over the progressive panels.
Whether this is enough to compensate for the restricted horizontal resolution is anyone’s guess, but it sounds like a damn good compromise to me. Near 100% greater vertical resolution (540-1024) with only about 30% less horizontal resolution (1364-1024)

If only they made AliS panels in larger sizes with at least 1600 horizontal resolution.

Flame suit on. :blink:

#17 tamarasue

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Posted 18 August 2005 - 05:26 PM

I find that on my 1024x1024 plasma, at 576p (native channel 7), the picture looks un-natural. If someone is walking from the left of the screen to the right, there head is elongated when at the ends of the screen and round in the middle! If I watch too long, I get almost sea sick!

I find 1080i clear and well proportioned.

#18 Doug

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Posted 18 August 2005 - 06:39 PM

On my ALIS panel I prefer the 720p over the 576p and 1080i.

It gives a sharper image.

#19 AdrianW

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Posted 18 August 2005 - 06:57 PM

I find that on my 1024x1024 plasma, at 576p (native channel 7), the picture looks un-natural.  If someone is walking from the left of the screen to the right, there head is elongated when at the ends of the screen and round in the middle!  If I watch too long, I get almost sea sick!

I find 1080i clear and well proportioned.

<{POST_SNAPBACK}>

That sounds like you haven't got the panel set to a true 16:9 mode, more like a 4:3 stretch mode (Panasonic calls the mode "Just"). Try changing the aspect mode on the panel.

#20 :)

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Posted 18 August 2005 - 07:06 PM

That sounds like you haven't got the panel set to a true 16:9 mode, more like a 4:3 stretch mode (Panasonic calls the mode "Just"). Try changing the aspect mode on the panel.

<{POST_SNAPBACK}>


I'd say so too as have a hitachi too running of a teav dvb800 as well and definetely don't see what your seeing there tamarasue.

make sure you got the setting via the zoom button on 'full' as opposed to panorama or anything else which will all give some strange effects. otherwise might be someother issue there.

#21 phreek

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Posted 18 August 2005 - 07:24 PM

Can we do an experiment amongst 1024x1024 ALiS panel owners.

When you input 720p vs 1080i can people comment on the size of the onscreen menu from their STB.

Is it (making sure the panel mode is WIDE without orbiter on):

A> Same size in both modes?
B> Smaller in 720p mode?
C> Smaller in 1080i mode?

Also if you could specify which Panel and STB you have.

On my panel the 720p produces a smaller onscreen menu from the STB.

I'm yet to explain why, but knowing how other box/panel combos perform may provide a hypothesis at least.

#22 tamarasue

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Posted 18 August 2005 - 07:34 PM

Thanks guys, that fixed the problem right up! I did not realize you could change the aspect ratio when hooked up on DVI (thought it was locked up).

I'll keep my STB on AUTO output now, although, can't see any difference between 576p and 1080i setting when watching channel 7!

#23 tamarasue

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Posted 18 August 2005 - 07:36 PM

Can we do an experiment amongst 1024x1024 ALiS panel owners.

When you input 720p vs 1080i can people comment on the size of the onscreen menu from their STB.

Is it (making sure the panel mode is WIDE without orbiter on):

A> Same size in both modes?
B> Smaller in 720p mode?
C> Smaller in 1080i mode?

Also if you could specify which Panel and STB you have.

On my panel the 720p produces a smaller onscreen menu from the STB.

I'm yet to explain why, but knowing how other box/panel combos perform may provide a hypothesis at least.

<{POST_SNAPBACK}>


How do you input 720p? I thought channels were only 576p or 1080i?

#24 glenncol

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Posted 18 August 2005 - 07:39 PM

How do you input 720p?  I thought channels were only 576p or 1080i?

<{POST_SNAPBACK}>


Hey dude

You can output 720p to the panel by hitting the VFormat button on the Teac remote until it reads 720P on the screen

#25 tamarasue

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Posted 18 August 2005 - 07:46 PM

But then the screen goes blank? I only get picture in 576p, 1080i or AUTO. I figured this is because no-one broadcasts in 720p ? Am I doing something else wrong?