What is 720p? 1024 x 768 or 1366 x 768? - Page 2 - AVS Forum
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post #31 of 40 Old 04-23-2007, 08:11 PM
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Quote:
Originally Posted by Blackraven View Post

1080i is more like a 644p from what I've heard.

Although I did wish that:

Interlace = Progressive divided by 2

Making 1080i = 540p

Things would have been more simple that way but I guess that's what electronics really is about (complex mumbo-jumbo)


A 1080i at 60 Hz source can mean 1 of 3 things:

1) A true 1080i60 source (every frame a different point in time), giving equivalent 540p at 60 Hz, with a slight half-line (or one full 1080-line) flicker up and down, which can give an illusion of 1080 resolution on static frames, but does not do well on moving items.
2) 1080p at 30 Hz source, which is regenerated by interleaving the correct frames.
3) 1080p at 24 Hz source, regenerated by interleaving the correct frames, and doing inverse 3:2 pulldown. However, most TVs don't display as a multiple of 24 Hz, but display at 60 Hz instead, with a 3:2 cadence.

Flat panels are always progressive display. If the native signal is truly 60 separate time frames, then flat panels don't do 1080i very well (#1 -- though a CRT would work great).

Even for sports, is 1080i really 60 separate frames in time? For movies or the HD Discovery channel, we actually have situation #2 or #3, which flat panels are designed to work with (though about half don't do it well). 1080i60 and the 1080p (24 or 30) signals that it represents are in fact identical, provided the TV can put the signal back together into a progressive image properly.

So, only situation 1 is a problem. In the rest of cases, 1080i and 1080p are identical. Having said that, 1080p is usually best, as there is no chance for mangling the image when puting it back together.
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post #32 of 40 Old 04-23-2007, 08:45 PM
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Quote:
Originally Posted by audioNeil View Post

Even for sports, is 1080i really 60 separate frames in time?

Not frames, but fields. With 1080i60 video, you have 60 different fields, each acquired 1/60th of a second after the other. That's why 1080i60 video requires so much more bandwidth than 24p sourced content, which involves 48 unique fields per second (with repeat flags).

The 24p content -- like movies and series -- may do just fine in 11-13Mbps, but 1080i60 video often requires 18Mbps or more. Some NBC and CBS affiliates supply their feeds with 13-15Mbps, which produces an excellent picture on movies and series, but once they show 1080i60 video (i.e. sports), you get pixelization and macroblocking during movement.

Video-sourced content

In the case of video-sourced material such as sports, we have 60 different 1920x540 fields, all acquired at different points in time (separated by 1/60th of a second). Because the fields were all acquired at different points in time, they don't "match up" when there is any movement on the screen. Attempting to combine every two fields to form a 1080p30 image would result in severe combing. Some older (and many cheaper) TVs simply "bob" to display 540p resolution, by taking each field and making it a frame without adding any new picture information. That was the old/cheap way of doing things.

The better displays on the market interpolate new information to create a full 1080p60 signal through a process known as motion-adaptive deinterlace. Adjacent fields are compared to determine what pixels are in motion. Areas of the picture that aren't in motion -- such as background scenery that did not move in the previous 1/60th of a second -- can be weaved together at full 1080p resolution. Areas of the picture that are in motion -- and did move in the previous 1/60th of a second-- are created by bobbing, or in some cases, averaging the information in adjacent fields, and will vary in resolution between 540p and ~1080p. Whether pixels in motion appear as 540p or closer to 1080p depends on the rate of movement, as well as the quality of the video processor in the display. Not all processors do motion-adaptive deinterlacing equally well.

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post #33 of 40 Old 04-24-2007, 09:57 AM
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Quote:
Originally Posted by bfdtv View Post

Not frames, but fields. With 1080i60 video, you have 60 different fields, each acquired 1/60th of a second after the other. That's why 1080i60 video requires so much more bandwidth than 24p sourced content, which involves 48 unique fields per second (with repeat flags).
(snip)
Not all processors do motion-adaptive deinterlacing equally well.

Thanks for the clarification. I guess the processors have their work cut out for them, trying to figure out the 3 different situations. Motion adaptive deinterlacing sounds like the most difficult.
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post #34 of 40 Old 04-27-2007, 07:12 PM
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Originally Posted by RobsTV View Post

1080i = 540p

If 1080i = 540p and 720p > 540p does that mean 720p > 1080i?

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post #35 of 40 Old 04-27-2007, 07:32 PM
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Quote:
Originally Posted by Louisville S View Post

If 1080i = 540p and 720p > 540p does that mean 720p > 1080i?

No, that user's post was incorrect. See above.

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post #36 of 40 Old 04-27-2007, 07:43 PM
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Quote:
Originally Posted by Louisville S View Post

If 1080i = 540p and 720p > 540p does that mean 720p > 1080i?


In some cases yes. Deinterlaceing is not as easy as some may suggest.

Most 06 models did not do so well.

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post #37 of 40 Old 01-05-2009, 02:43 AM
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Originally Posted by doogiehowser View Post

What is 720p? 1024 x 768 or 1366 x 768?

First of all, these are 2 different resolution ratios:
1024 x 768 is a normal screen 4:3 (or 1.33 : 1 ratio), mostly used by PC monitors;
1366 x 768 is a 16:9 wide screen (or 1.77 : 1 ratio).

720p has nothing to do with any of these 2 resolutions.

The best explanations are given by martyj19 and PRMan.

gg all!
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post #38 of 40 Old 01-05-2009, 05:27 AM
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Why is the 1920 described as horizontal resolution, and the 1080 as vertical resolution? I would assume since the monitor is wider than taller, that the 1920 lines of resolution sit side by side in a vertical fashion, and the 1080 lines are stacked on top of each other horizontally. Perhaps this is the reason for the confusion where I see people describe it both ways and then you have others telling them they have it "backwards." Which is correct?
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post #39 of 40 Old 05-15-2009, 10:05 AM
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Originally Posted by facesnorth View Post

Why is the 1920 described as horizontal resolution, and the 1080 as vertical resolution? ... Which is correct?

Because the 1920 is scanned horizontally across the picture tube by the ion beam. The 1080 is scanned vertically down - at least it used to be in CRTs.
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post #40 of 40 Old 05-15-2009, 10:34 AM
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Quote:
Originally Posted by Louisville S View Post

If 1080i = 540p and 720p > 540p does that mean 720p > 1080i?



There is a lot of misinformation in this thread. First,

1080i > 540p

1080i has TWO 540 fields that are totally different, even for static shots. When the two 540 fields are combined into a frame you have twice the vertical resolution compared to a 540p display.

Secondly,

1080i = 720p

1080i has 50% more vertical resolution compared to 720p, however 720p updates its information twice as often giving twice the time resolution (useful for fast moving events). As a result, on fairly static subjects, 1080i is better because it offers more detail, on fast motion, 720p is better because it more accurately follows the motion. The net effect is to make these two seeminly different resolutions provide about the same information content; as such they are approximately equal in quality. Sports would benefit more from 720p and romantic sunsets will benefit more from 1080i - pick according to your use.
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