1080p vs 720p

Hi, I get the difference between 720 and 1080p resolution, but I dont understand why 720p even exists. The salesman told me that when they went to bigger screen size they needed more pixels because the spacing between the pixels was getting to far apart. So they doubled the rez and 1080p was born. The thing is I want a 32" and just about all of them are 720p. I know there are some at 1080p but at almost twice the price. Why have 720p? When color came out we didnt have full color and half color. What Im afraid of is when I get a 720p they will finally find away to broadcast 1080p and Ill have to get a new tv. I know its a bandwidth problem now but not for long I bet. I have also heard not many tv's can correctly de-interlace a 1080i signal to 720p now so I think this could be a problem. What do you guys think?

720p exists because of the ATSC standard, which defines what resolutions HD broadcasts can be in. There are a number of resolutions included in that standard, but the two that everyone uses are 720p and 1080i. When folks started building HDTV's, the early LCD, plasma, and DLP solutions became very expensive if they were built to operate at that 1080 resolution (1900x1080 pixels), so it became common to do a reduced resolution (768 "lines") to be more cost effective. On smaller displays, this has continued and will likely still do so for some time to come, because the cost premium to build a 32" 1080p LCD flat panel is significant without offering an appreciable benefit over 768p at typical viewing distances.

I'll offer a few random observations about shopping for a 32" TV right now. First, HD broadcasts will mostly stay at 1080i, and the few that go to 1080p will simply be deinterlacing 1080i or scaling 720p in almost every case - 1080p content will be scarce. Second, all HDTV's have to be able to scale and deinterlace. Sure, some are better at it than others, but they all need to be able to accept a 480i, 480p, 720p, or 1080i signal (and in most cases today a 1080p signal as well) and manipulate it to the native resolution of the display. As a result, broadcasting at 1080p will not make 720p displays obsolete. The only difference between broadcasting at 1080p and at 1080i is that 1080p means your TV doesn't have to do any deinterlacing. Since the scaling process is easier (relatively speaking) than deinterlacing, it's hard to say that you are losing anything.

As far as I know 1080p is not part of the broadcasting standards for HD, so don't expect it to come out of your cable or satellite box anytime soon. It would have to be 1080p 60fps to make a difference anyhow as you will have a very hard time telling the difference between 1080p 30fps and 1080i 30fps (which is the max that 1080i will do using 60 half frames a second).

They did not start making 1080i sets because they reached limits of 720p display technology. 720p and 1080i have always been a part of the HDTV spec. The older generation CRT HDTVs were all capable of handling 1080i (a lot were not capable of displaying 720p natively at all though).

I'd also like to say that for a 32" TV you'd have to sit very close to get the full detail of 1080i (4' in fact according to my favorite distance calculator http://myhometheater.homestead.com/viewingdistancecalculator.html). So unless you are planning to sit that close, you won't need a 1080 display.

Having said that, and being the owner of a 50" display that I'm sitting 7-8' away from, you can never get big enough. Go with the largest display that you can afford and that fits your space.

32" is not that big for a 16:9 display.

Actually, there is one satellite service now being pitched as providing 1080p. It has the same bandwidth limitations as any other, though, and the ads I've seen don't mention compression algorithms being used to tell how much squeezing they're doing.

They can claim all they want and perhaps it's possible that they are broadcasting at 1080p/30 for movies, but there's no broadcast or cable TV recorded in that format, so any regular TV will be the same on a 1080i set vs a 1080p set.

Also as far as practical matters go, 1080p/30 is the same thing as 1080i/60(60 half frames per second).

About the only time I've heard of 1080p holding an advantage is for some PS3 games that are displayed/rendered at 1080p/60, which cannot be done through 1080i.

BloggingITGuy your link for your favorite calculator did not work. I found myself re-directed to some web page development site.

Yeah, the ")." at the end got added. Try this http://myhometheater.homestead.com/viewingdistancecalculator.html

That worked. Thanks BloggingITGuy.

Isn't 720p superior to 1080i???...I thought if the native resolution was 720p it was just that whereas 1080i was doubling 540 (to get to 1080i)...have I got this wrong???...I can get both 10801 and 720p but can't see a whole lot of difference...
...also, should I be holding off on BluRay if I have a 720p/1080i set (50" rear screen projection Sony)
Bill

The opposite, actually - 1080i has more pixels than 720p, it just redraws them differently (each pixel gets redrawn 30 times in a second rather than 60 times).
The 1080/540 thing you are thinking of may be related to the early 1080 rear-projection displays, back when 720p (or, more exactly, 768p) was the standard - if I remember correctly, they weren't able to put enough pixels on a chip to do 1080 lines, so they did 540p and used that to draw 1080i by alternating. It's been a while since I looked at that issue, though.
I'll counter with a similar question: should I have held off on buying DVD until I had a TV with component video inputs? In both cases, I would answer "no" - in the case of Blu-ray, you have an HDTV and it will give you the best picture it possibly can if you feed it a true HD source. Just because the best results in your case may come from scaling down to 720p output doesn't mean you shouldn't do it.

gonk,

As always I appreciate you expertise...so I can change the TV to 1080i on my AT&T U-Verse (I can get 1080i)for a better picture???...

Perhaps I will look into a BluRay player which may be priced a bit better after Thanksgiving...

Thanks!
Bill

You can give it a try - but it is possible you will like the 720p picture more if your TV's native resolution is 720p (or 768p) depending on the quality of the scaling and deinterlacing at different points in the signal path. If you output 1080i from your AT&T box, the TV will deinterlace it and convert it to its native resolution. If you output 720p from your AT&T box, the TV will still do some scaling but the AT&T box will do deinterlacing and scaling for any HD sources that are natively 1080i. If the TV has a better scaler and deinterlacer than the AT&T box, it's very possible that 1080i will look better.

thanks...
Bill

Hey gonk,

If you are referring to the earlier 1080i DLP chips that used wobulation to get to 1080i, the wobulation was actually done on the 1920 (horizontal lines) by using 960 pixels that wobbled back and forth to approximate 1920x1080.

This is why, when I bought my SXRD Sony 50" there was a clear and noticeable difference between it and the "1080" Mitsubishi right next to it.

That's what it was! Thanks, it had been so long I'd forgotten quite how their wobulation technique worked. So it was 960x1080 instead of 1920x1080, compared to 1388x768 (or one of the other 768 variations) that was standard at the time.

Right. We didn't see true 1080 fixed pixel (non-CRT) sets until Sony and JVC came out with their LCoS RPTVs.

No Gonk you were correct originally. Many of the original CRT based rear based projectors (at least Toshiba's) were based upon a 540p capability and used that to render 1080i. I don't recall the technical details but it was not wobulation which Blogging accurately displayed.

I am guessing it was easier in the early days of HDTV to produce a 540p device then a 720p. It also may be related to PAL and the original Japanese HDTV devices that were all analog.

Wobulation was used only on DLP sets.

As for CRT HDTVs, I can't comment on whether they were truly 1080i capable or if they just displayed each field (half-frame) on the same 540 lines.

Seems kind of preposterous as they'd still need 1920 lines for the width of the picture...then again I guess it's easier to do 1920x540 as opposed to 1920x1080.

IMHO, no one can buy a monitor that will handle all standards that might come into consumer usage for the life of the monitor, without adding/updating electronics that will aid in the process of converting to the native resolution of the display. The HDMI 1.3 standard has already made room for 2560x1600, and 3840x2400 for some special displays is not that far off. Although these increased resolution standards are not just around the corner in the entertainment mass market, some segments of the industry are preparing for the day.

Bottom line: if you 'must have' some of the best available, you'll have to keep spending as 'even better' comes to market. Question: how much 'better' will make a difference?

Correct me if I'm wrong, but early on in the HD evolutionary process, 720p was deemed to be better for sports due to the fact that it was 720p/60, while, as previously stated, 1080i/60 is effectively 1080p/30. Seeing a hockey puck move in 60fps vs. 30fps provided clearer tracking. That is why Fox/ESPN broadcast in 720p.

Also, as stated above, it is likely that any 1080p broadcasts are likely 1080p/30 due to the bandwidth required to broadcast 1080p/60, but they'll never tell you how many fps they're broadcasting in!

FYI. Here is a very helpful link to a chart that gives distances and screen sizes for viewing the different HD resolutions. It is based on the ability of the human eye to see detail:

http://hdguru.com/hdtv-seating-distance-chart/6/

Basically, it tells me that I need to be sitting 7 feet from my 55" SXRD to see a difference between 1080p and 720p.

I like this calculator better: http://myhometheater.homestead.com/viewingdistancecalculator.html

Yep...and if you are sitting farther away than that your TV is too small. At least if the goal is to turn your living room in to a home theater.

You need to sit pretty close to a 50", 55" or even 60" TV to get the same effect as sitting in the middle of a theater.

I would love to have bought the 70", but my goal was to create the best home theater I could for the money, room constraints, spousal limitations, and etc!

The original question of this topic was whether 720p was a waste of money and I believe that most people don't realize that for most living room applications, 720p is going to provide the same level of performance as 1080p. But those of us who are fans of home theater can't resist the "more is better" syndrome (myself included).

As we all know, resolution is only one factor in picture reproduction. Unless you're looking to have a front projector in your theater set-up (which some people in this forum do!), there are other factors that will affect the performance of a HDTV picture more than whether it is 720P or 1080p.