High Def Forum
Thank you for visiting. This is our website archive. Please visit our main website by clicking the logo above.

1080 vs 720

07-09-2004, 02:08 AM
Hi there. This may be a stupid question, but..

I just hooked up an LG 'HD' set-top box to my Sony 'HD' widescreen TV. When I have the LG box set to 1080, the picture is cropped off on one side (not centered). The problem is fixed when I switch the box to output 720.
I'm sure my TV is capable of accepting 1080.. so what's the problem?
Should I just leave it on 720? What's the difference in resolution?

Any advice greatly appreciated.


07-09-2004, 02:28 PM
It's not a stupid question, but it is incomplete. What is the connection you are using between the two? Component, VGA, DVI, etc. Also the model numbers of the equipment may help us as well.

As far as the resolution question, it used to be thought of as the best between the two would be 720p based on progressive scanning vs interlaced. Because of computer monitors needing to be progressive scanned to avoid flicker, it was assumed for years this carried on to HDTVs as well. In fact due to different persistance of phosphers and other issues, it is generally considered the two formats are about equal and most crt based TVs actually display at 1080i no matter what input is supplied. In your case I suspect the TV will display using the 720p format no matter what it receives. I'd say based on what you have said to leave it at 720p and be happy!

07-10-2004, 12:28 AM
Thanks for the great answer..

My TV is a 36" Sony HD CRT, model number: KVHR36M31. I'm in Australia, so not sure if model numbers change for region. My LG set top box is LST4100P.

I'm guessing that the TV is happier with a progressive signal? As opposed to interlaced..

I'm more than happy with 720p.. it looks great and to be honest, I can't see any difference when I flick it to 1080i..

I have connected them with component (blue, red, green) and audio (white, red).

That actually reminds me of another question! What are the other two inputs for? - I think they are marked 'V and H' from memory. No set-top boxes had this many outputs.


07-10-2004, 08:22 AM
Those are for separate vertical and horizontal sync signals. Not many sources outside the broadcast industry use this method of connection. With the three component connections the sync signals are superimposed on one of the three cables and separated inside the TV. Usually this requires a menu setting in the TV to select which connection you are using and that may be the reason you are getting the symptoms you described. Worth checking.

Your TV will probably not be able to display any better picture at 1080i than it will at 720p. Since it is a crt based unit, most likely it is doubtful if you are able to get the full 1380 x 720 resolution of the HDTV spec anyway. If you were to connect a computer to the TV through the approprate adapter, you would probably find out that the crt is limited to about 800 x 600 actual resolution. The reason for me saying this is that most crts are made to very simular specifications and the shadow masks in the crt will not allow a dot small enough to get to the 1380 x 720 resolution. This is true for most RPTVs as well. The beams comming off of the cathodes in the crts would produce the desired resolution if there were holes in the mask in the proper places. If you can find this sort of information (dot pitch) for your TV it would allow the max resolution to be calculated. Most manufacturers do not publish it. Use the 720 setting and be happy, cause it is most likely as good as it gets.

07-11-2004, 07:43 PM
Thanks again. You've been a great help.

07-12-2004, 12:46 PM
720p is 720 lines 30 x a second.

(If you can get genuine1080i output) 1080i is 540 lines then another 540 lines interleaved (interlaced) each one 30 x a second, total 60 frames in one second.

so really that is 540 lines against 720.

hope this helps


07-12-2004, 02:29 PM
so really that is 540 lines against 720.And that is what the progressive scan advocates say to enforce the notion that 720p > 1080i. And what is left out of the equation is a number of things that enter into the formation of a picture in one's mind that cannot be expressed in numbers alone. For example if we are looking at a still photograph then the fact that the 1080 lines are painted in the interlaced manner will not matter as much because there will be no motion distortion from one scan to the next and the 1080 total lines will produce better picture detail over the 720 lines. Additionally there is the matter of horizontal resolution that comes with the additional lines. The 1080i is 1920 pixels wide versus 1380 for the 720p spec. Also most phosphor persistence for TVs is timed for the interlaced scan rates to reduce flicker (unlike computer monitors that have a lot lower persistence) so the interlacing is not as big a factor as the computer guys (who started the issue of progressive vs. interlaced in the first place) would have us think. There is the issue of motion distortion where a moving object has moved slightly from the first 540 lines to the second 540 lines. But considering the increased number of pixels there is a smaller difference (distortion) than if we were talking about 720 lines interlaced. So generally the two formats are considered about equal.

Another consideration is one of bandwidth of the delivering medium. In the case of OTA signals the compression ratio required for the two formats is about the same - 993,600 pixels for the 720p and 1,036,800 for each 540 lines of the 1080i. This introduces another possible distortion, which gets aggravated at faster motion. So what the progressive scan may have given you at 720p, the bandwidth can take away.

07-20-2004, 06:21 PM
720p can be 30fps OR 60fps

1080i can be 30fps or 60fps

07-20-2004, 06:28 PM
720p can be 30fps OR 60fps

1080i can be 30fps or 60fps


720p can be 24fps,30fps, or 60fps

1080i is 30fps


Dopius Fishius
09-25-2004, 07:52 AM
Hey All,

I just got a Plasma Display and the HD Box mentioned, the LG LST4100P and with a component output it gives me the same problem! It crops a bit off the right hand side of the screen at 1080i but works normally in every other mode.

The interesting part is, that with the RGB output (which my plasma accepts) at 1080i, this doesnt happen.

I will be returning the set top box tomorrow, since I expect to get a product without problems for the price I have paid.

Just thought you would like to know incase it comes up again.


12-23-2007, 04:28 AM
Hey all.
I would like to add a question and ask for help :
if shooting with the Hdvx200 in order to transfer to film,
what is best , to shoot in 1080i/25p or 720p/25p and why ?

thx in advance .