1080p- Does it matter?

1080i vs. 1080p: It’s all a matter of time.

1080i is the highest resolution format of the HDTV ATSC specification as well as the recently launched HD DVD and Blu-ray media. 1080p is often quoted as being a higher resolution than 1080i, and though from a certain point of view (which we will touch on) that’s true, in the broad context it is not.

In a very real way, 1080i and 1080p are the same resolution in that both consist of a 1920 x 1080 raster. That is, the picture is comprised of 1080 separate horizontal ‘lines’, with 1920 samples per line (or pixels per line, depending on your point of view). In other words, both 1080i and 1080p represent an image with 1920 x 1080 unique points of data in space.

The difference between ‘i’ and ‘p’ can only be appreciated in the time domain.

In a “true” or “native” 1080i HDTV system, the temporal resolution is 60 Hz. The image is sampled, or updated if you prefer, every 1/60 of a second. As with any interlaced format though, only half the available lines are sampled, or updated, every 1/60 of a second. The capture device (say, a video camera) does not sample the entire 1920 x 1080 at one time. Rather, it samples fields. A single field consists of every other line out of the complete picture. So we have the “odds” field which has lines 1, 3, 5, 7, etc and the “evens” field which has lines 2, 4, 6, 8, etc.

So, in an interlaced system, the camera samples one field (say the “odds”), then 1/60 of a second later, it samples the opposite field (the “evens”), then 1/60 of a second later it refreshes the odds, then 1/60 of a second later the evens, and so on. The alternating set of fields of a 1080i source each make up half the image.

The shorthand for this format is 1080i60.

The subject being captured is updated every 1/60 of a second, but only half the lines are used for each update. This has one benefit and many drawbacks.

The one virtue of this format is its high subject refresh rate: Think of a sporting event where the ball is traveling fast. We get an update on its position every 1/60 of a second. That’s really good compared to film’s 24 Hz refresh rate (even IMAX HD is only 48 Hz).

The downside on an interlaced format is that the alternating fields only truly compliment each other if the subject is stationary. If it is, then the alternating fields “sum” to form a complete and continuous 1920 x 1080 picture (everything lines up perfectly between the two fields). If the subject moves though, it will be in one position for one field and another position for the next. The interlaced fields no longer compliment one another and artifacts such as jaggies, line twitter, and other visual aberrations are a normal side effect of the interlaced format.

This animation demonstrates how objects in motion end up in a different position for each field, resulting in the “comb” effect.  Note however that areas not in motion maintain “full” resolution	This animation simulates the “twittering” of detail, inherent to an interlaced display system.

What does all this have to do with 1080p?

1080p differs from 1080i in that the entire 1920 x 1080 raster (all of the 1080 lines side to side) is sampled and/or displayed at one time. No fields. Just full, 1920 x 1080 frames. No combing. No line twitter. Just perfect pictures. But how, if our HDTV system does not incorporate 1080p does it become at all relevant?

We’re going to show you.

First we will explain how and why 1080i must be processed as best as possible into 1080p in order to maximize the potential of today’s digital displays, including LCD and Plasma flat panel TVs, as well as LCD/DLP etc, projection systems.

Let’s look at some illustrations:

If this were a scene shot at 1080i, and displayed at 1080i, it would look like this.  But today’s digital TV’s cannot do this.  The signal must be de-interlaced.
If we de-interlace it the WRONG way, it would look like this. The entire scene is reduced to 540 lines worth of resolution. Hint: look at the hands. If you display this on a 1366×768 TV (a common resolution right now), you will be wasting 1/3 of the resolution you paid for!
If we de-interlace it the RIGHT way though, to 1080p, it would look like this. Only the areas in motion are reduced in detail.  The rest remains at the full 1080 line resolution. Though you need a full 1920 x 1080 TV to maximize the detail present, on a lesser TV, say a 1366 x 768 model, you will still realize the device’s full potential.

Still wonder if you should care about 1080p?

But do you really need it?

Well, the first thing to come to terms with is, that, as we’ve pointed out, there is an abundance of 1080p24 material out there, encoded into 1080i60 format. If you want to view it at its full potential, you need not only a device capable of displaying it, a so called 1080line TV, but the ability to actually de-interlace it properly.

Some will argue that if you are seated far away and/or the screen is not enormous, one won’t “appreciate” the full detail of 1920 x 1080 (as compared to lower resolution TVs). Well, if you look at a 27″ 480i TV from 20 feet away, you could make the same argument. We could also make the argument that most people don’t appreciate, or even know of, reasonably good video quality to begin with. The strongest argument for that is to look at the quantity vs. quality of channels available from your satellite or cable provider in standard definition digital format vs. a good DVD in the same format, or even a standard definition terrestrial broadcast with a reasonably good signal. Even the most massive compression artifacts are apparently acceptable enough to most viewers such that most broadcast content providers fill up bandwidth with hundreds of programs (and maximize compression to do it) with little complaint from their subscribers.

In that realm, if that’s your baseline, then yes, the 1080p vs. 1366 x 768, or whatever your number, is more of a feel good numbers game. But, that’s not us, and if you’re reading this, we’re betting that’s not you either.

The point is, if you want to view the inherently 1080p24 content which is out there (and even native 1080i content) with maximum resolution (and we maintain that an enthusiast who sets up their viewing environment to get the most out of it can see the difference), you need a display capable of 1080p that keeps the signal in a 1080 line format from input to display surface.

(Article Source: http://www.hometheaterhifi.com/volume_14_1/feature-article-1080p-3-2007-part-1.html)