HDTV Technical > 720p vs 1080i Cable on 1080p TV
Shadowboricua's Avatar Shadowboricua 02:55 PM 12-14-2008
My cable box can output to both 720p and 1080i. I have a Sony Bravia 42V4100 capable of full 1080p. What is the best setting to use? 720p or 1080i for cable TV? I mostly watch FOX, ABC, NBC, TPT/PBS on HD. Any takers?

I know that the differences are barely noticeable, I just want to know which is technically the most optimal setting. Thanks in advance.

walford's Avatar walford 03:03 PM 12-14-2008
If you select either 720p or 1080i which is common for a Motoroloa cable box then you certainly want to use 1080i so as to get the full 2 megapixel per frame to your 1080p TV.
You certainly do not want to have delete have of the detail from 1080i cable channels by outputting them in 720p only to have your TV try to revent the content you deleted in order to upscale the 720p to 1080p.
NetworkTV's Avatar NetworkTV 03:05 PM 12-14-2008
Neither is the best setting. Let the box send them as is and let your TV scale them.
gbynum's Avatar gbynum 03:06 PM 12-14-2008
Quote:
Originally Posted by Shadowboricua View Post

My cable box can output to both 720p and 1080i. I have a Sony Bravia 42V4100 capable of full 1080p. What is the best setting to use? 720p or 1080i for cable TV? I mostly watch FOX, ABC, NBC, TPT/PBS on HD. Any takers?

I know that the differences are barely noticeable, I just want to know which is technically the most optimal setting. Thanks in advance.

I'd bet that the Sony does a better upconversion from 720P to 1080P than the box from 720P to 1080i then the Sony to 1080P. I _PERSONALLY_ have found that feeding the TV the native format and letting it do the work is better.
Shadowboricua's Avatar Shadowboricua 03:08 PM 12-14-2008
Quote:
Originally Posted by walford View Post

If you select either 720p or 1080i which is common for a Motoroloa cable box then you certainly want to use 1080i so as to get the full 2 megapixel per frame to your 1080p TV.
You certainly do not want to have delete have of the detail from 1080i cable channels by outputting them in 720p only to have your TV try to revent the content you deleted in order to upscale the 720p to 1080p.

So displaying at 720p makes halves the resolution on a 1080p even though it is display fullscreen? please excuse my ignorance...

Are the broadcasters doing 720p or 1080i? What if the stations broadcast at 720p, is is still better to send it 1080i to the TV?
Shadowboricua's Avatar Shadowboricua 03:09 PM 12-14-2008
Quote:
Originally Posted by gbynum View Post

I'd bet that the Sony does a better upconversion from 720P to 1080P than the box from 720P to 1080i then the Sony to 1080P. I _PERSONALLY_ have found that feeding the TV the native format and letting it do the work is better.

The box does not allow me to send native format to TV? how do you do that?
NetworkTV's Avatar NetworkTV 03:14 PM 12-14-2008
Quote:
Originally Posted by Shadowboricua View Post

The box does not allow me to send native format to TV? how do you do that?

If both resolutions are selected in the settings menu, it will send both.

Quote:
Originally Posted by Shadowboricua View Post

So displaying at 720p makes halves the resolution on a 1080p even though it is display fullscreen? please excuse my ignorance...

Are the broadcasters doing 720p or 1080i? What if the stations broadcast at 720p, is is still better to send it 1080i to the TV?

Not quite.

While 1080i has more lines total, they're split between two fields that are each scanned one at a time to create one full video frame each second. 720p sends all the lines in one scan, but does it twice as many times per second as 1080i. So you get around 480 lines twice each second with 1080i and 720 lines twice each second with 720p.

All the Disney Owned stations (ABC, ABC Family, ESPN, Disney Channel, etc), all the Fox stations (Fox, FX, Fox News, etc.) as well as the History channel are 720p. Pretty much everyone else is 1080i.

Send both formats to the TV and let the TV deal with it. 720p will be uprezzed to1080p and 1080i will be converted to 1080p.
Shadowboricua's Avatar Shadowboricua 03:17 PM 12-14-2008
Quote:
Originally Posted by NetworkTV View Post

If both resolutions are selected in the settings menu, it will send both.

I guess my box is not that good. It does not have that option, as fas as I can tell. So with my set up, which is the best 1080i or 720p?
Scooper's Avatar Scooper 03:27 PM 12-14-2008
Whatever looks best to your eyes on your equipment.
Shadowboricua's Avatar Shadowboricua 03:29 PM 12-14-2008
Quote:
Originally Posted by Scooper View Post

Whatever looks best to your eyes on your equipment.

If you look at my OP you will see that I want to know which option is the most TECHNICALLY optimal with my set-up, not SUBJECTIVELY optimal...
NetworkTV's Avatar NetworkTV 03:35 PM 12-14-2008
Quote:
Originally Posted by Shadowboricua View Post

I guess my box is not that good. It does not have that option, as fas as I can tell. So with my set up, which is the best 1080i or 720p?

What brand and model box do you have? Someone here can help you set it correctly. The settings are in there somewhere.
Shadowboricua's Avatar Shadowboricua 03:41 PM 12-14-2008
Quote:
Originally Posted by NetworkTV View Post

What brand and model box do you have? Someone here can help you set it correctly. The settings are in there somewhere.

It is a Motorola DCT6200. It is connected to my TV by component, no HDMI available in this stupid box.
NetworkTV's Avatar NetworkTV 03:46 PM 12-14-2008
Quote:
Originally Posted by Shadowboricua View Post

It is a Motorola DCT6200. It is connected to my TV by component, no HDMI available in this stupid box.

Go HERE.

The instructions are on page 24.
Shadowboricua's Avatar Shadowboricua 03:56 PM 12-14-2008
Quote:
Originally Posted by NetworkTV View Post

Go HERE.

The instructions are on page 24.

Thanks, I actually know how to change the settings from the different outputs, but there is no setting that allows you to select multiple, like you were saying before.
NetworkTV's Avatar NetworkTV 04:23 PM 12-14-2008
Quote:
Originally Posted by Shadowboricua View Post

Thanks, I actually know how to change the settings from the different outputs, but there is no setting that allows you to select multiple, like you were saying before.

I'd see if they have a better box, then.

That thing is a pile of junk.

If it doesn't have the most basic features, the scaler in it isn't going to be anything to write home about, either.

Take the box in and ask...no, demand another one. You're paying good money for HD service. Get your money's worth.
Shadowboricua's Avatar Shadowboricua 05:06 PM 12-14-2008
I guess nobody really knows the answer.
walford's Avatar walford 05:11 PM 12-14-2008
Since you have a 1080p TV and with your model cable STB you do not have a pass through option you want to to send it 1080i(1920x1080 interlaced). You do not want to eliminate half of the detail by sending 720p (1280x720). ABC, FOX and ESPN HD broadcast in 720p. CBS, NBC and the other broadcast HD in 1080i.
Interlaced video means that the frames are tranmitted in two fields the even lines and the odd lines and a digital technology TV puts them back together in its own output buffer so as to display them in 1080p.
coyoteaz's Avatar coyoteaz 09:55 PM 12-14-2008
Quote:
Originally Posted by NetworkTV View Post

I'd see if they have a better box, then.

That thing is a pile of junk.

If it doesn't have the most basic features, the scaler in it isn't going to be anything to write home about, either.

Take the box in and ask...no, demand another one. You're paying good money for HD service. Get your money's worth.

What a ridiculous answer. If the cable company is providing the 6200, they're almost certainly only going to have other Motorola boxes available, none of which have Native mode.

To the OP, either setting will cause some loss of detail when watching a channel that uses the opposite format, so the best answer truly is to pick whichever looks best to you on what you watch most. Personally, I use 1080i but will change to 720p if I'm planning to watch ESPN all day. Most Moto boxes have a service menu accessible by turning off the box then pressing OK then Menu on the remote. This will allow you to change the resolution faster than digging through 4 levels of menu to do it the normal way. Just remember that it's not in idiot mode, so anything you adjust will change immediately with no confirmation required, so don't go fiddling with the other settings.
gbynum's Avatar gbynum 05:29 AM 12-15-2008
Quote:
Originally Posted by Shadowboricua View Post

I guess nobody really knows the answer.

The answer is to use 720P on 720P sources, and 1080i on 1080i sources. The "technically best" you request is not definable, but as several of us have suggested, the set likely has better scaling algorithms than the Motorola box. It REALLY IS an issue of which does what and how, with given program material, is better TO YOUR EYES.
Shadowboricua's Avatar Shadowboricua 05:58 AM 12-15-2008
Thanks guys. I guess that I am back to where I have been since the beginning. I've had the setting on 720p on the cable box since I got the TV, recently I changed it to 1080i. Still trying to decide "what looks better to my eyes".

Anyway, what happens when you display 720p on a 1080p? Does the TV interpolates to 1080p to make it fill the screen? Thanks in advance.
walford's Avatar walford 07:45 AM 12-15-2008
Yes the TV upscales the 1280x720 frames to 1020x1080 frame picture quality therefore is much poorer then if 1080i programs were sent direct to the TV without downscaling to 720p since no pixel content has to be invented.
coyoteaz's Avatar coyoteaz 11:53 AM 12-15-2008
1080i content shown on a 1080p display has to have content invented too. The source only has 1920x540 pixels updated every 1/60 of a second, and the TV has 1920x1080 pixels updated every 1/60 of a second.

1080i loses 1/3 of its horizontal resolution, and 1/3 of the vertical resolution on a still shot (or none on a shot with motion) when converted to 720p. 720p loses 1/3 the vertical resolution when converted to 1080i. Either way, the max effective resolution is 1280x540. Whether the source actually has that much effective resolution to begin with is highly dependent on what it was shot and edited on, and how badly your provider is abusing compression.
Shadowboricua's Avatar Shadowboricua 01:07 PM 12-15-2008
Great, thank you for the explanation.
walford's Avatar walford 01:45 PM 12-15-2008
Quote:
Originally Posted by coyoteaz View Post

1080i content shown on a 1080p display has to have content invented too. The source only has 1920x540 pixels updated every 1/60 of a second, and the TV has 1920x1080 pixels updated every 1/60 of a second.

1080i loses 1/3 of its horizontal resolution, and 1/3 of the vertical resolution on a still shot (or none on a shot with motion) when converted to 720p. 720p loses 1/3 the vertical resolution when converted to 1080i. Either way, the max effective resolution is 1280x540. Whether the source actually has that much effective resolution to begin with is highly dependent on what it was shot and edited on, and how badly your provider is abusing compression.

I disagree with your explanation, 1080i consits of two fields the even numbered line field consisting of the 1920x540 even lines in a 1080p frame and the odd nubered line field of the the 1950x540 odd lines in a 1080p frame.
So when the input is de-interlaced by putts the 2 fields back together again in 1080p buffer you get full 1920x1080 frame at 30 frames per second. It is true that with a video(non film) source that the two field are 1/60 of a second apart in time so motion compensation is often applied to correct for this. But at no time is any scaliing of the created 1080p buffer performed.
Since HDTV do refresh their 1080p displays at 60Hz the HDTVs de-interlace using each filed twice once with the previous field and once with the next field this enables them to display 60 frames a second from a 30 frame per second 1080i input stream.

My description above describes how Weave de-interlacing works.
Most 720P HDTVs and many older 1080p HDTVs used bob de-interlacing which scaled each 1920x540 field separatly to a 720 frame or to a 1080p frame in. This technioque was used in order to save memory buffer space and graphic processing power in these models.
Almost all if not all current generation 1080p HDTVs use weave de-interlacing since it produces full 1920x1080 frames without using doubling or interpolating the content of existing lines to upscale resulting in much better quality video.
coyoteaz's Avatar coyoteaz 08:41 PM 12-15-2008
You can only weave when both fields are taken from the same moment in time, which limits you to 30p native content, which simply isn't common. The only shows I can think of that are 30p are Survivor and the Victoria's Secret Fashion Show. Everything else (ignoring converted 50Hz sources) is either 24p with 2:3 pulldown applied to get it to 30i, or 30i native. Some new TVs can correctly reverse the 2:3 pulldown to restore 1080p24 video, but it's not universal in 2008 models, and it's not common in 2007 and earlier models.

As for 30i content, it must be deinterlaced, and weaving isn't going to cut it. Also, the result of the deinterlace needs to be 60fps, not 30. The entire point of interlacing is to allow for fluid motion capture at 60Hz without needing twice the room to do it, and if display devices are going to simply throw away half of that, there would be no reason to do it in the first place. Most progressive TVs simply bob interlaced content, though newer ones are starting to use algorithms involving motion compensation. For better or worse, you're still relying on the device to create content that wasn't present in the source.
walford's Avatar walford 06:29 PM 12-16-2008
When I stated in my above that Weave de-interlaing with motion compensation needed to be use in order to handle the conversion of 1080i content to 1080p frames it apears that is much better descriped as Adaptive de-interlacin
Also as I stated above 1080i 30 fps content is converted to 60 fps second output by using each 1080i field twice they do this as follows:
1080p frame 1 is deinterlaced from 1080i even field 1 with 1080i odd field 1
1080p frame 2 is deinterlaced from 1080i odd field 1 with 1080i even field 2
1080p frame 3 is deinterlaced from 1080i even field 2 with 1080i odd field 2
1080p frame 4 is deinterlaced from 1080i odd field 2 with 1080i even field 3
and so forth so that 60fps output is created from 30fps input.
It is also important to note that current generation of HD studio cameras can capture 1080p/60 and rhwn output either
1080p/60, or 1080i/60, 720p, 480i or 480p doe further processing prior to tranmissionl
So a station has a choice of creating 1080i/60 output from 1 single 1080p/60 frame
or from a even and odd fields from 2 consecutive 1080p frames in order to provide for adaptive deinterlacing to provide PQ when motion content is present.
coyoteaz's Avatar coyoteaz 08:30 PM 12-16-2008
That's more accurately referred to as double weave. Weave is simply combining the 2 fields into a single frame, which is mostly used in 50Hz areas where 24p content is sped up to 25p, then processed through 2:2 pulldown into 50 fields/sec. A weave brings it back to 25p with no loss of resolution or creation of new content.

Using a double weave still doesn't change the fact that the deinterlacer is creating content that isn't there. The goal of a motion-adaptive deinterlacer is to use information from both fields to construct a complete frame that occurs between the 2 fields time-wise (an average of the frames if you will), not unlike how Sony's Motionflow and Samsung's Auto Motion Plus create 120Hz motion from 24 or 60Hz sources. Yes, if done correctly it results in better resolution than a straight bob since non-moving areas will retain higher resolution, but it's still not going to approach 1080p in anything with motion.
John Mason's Avatar John Mason 06:36 AM 12-17-2008
Just to clarify: Although some shows, such as the CBS reality one from Gabon, Africa, are captured at 30p, assume no one's saying they're not being converted to 1080/60i for transmission (for 1080i transmission sources)? Seems that 1080/60i capture--for example, Sony HDCAMs--would be better as far as smoother motion; recall reading here they're using Sony solid-state (tapeless) camcorders in Gabon. Suppose 30p capture gives a somewhat more filmic quality, although those with 1080i CRT displays would still be viewing images at 1080/60i, just as with viewing 24p pulldown fields (most 24p-captured programming) at 1080/60i (with 30i fps through eye/brain fusion). -- John
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