720p vs 1080p: Which should I buy?

A few years ago we wrote a column about HDTV resolution and whether you should just buy a "standard" 720p/1080i set or pay the extra bucks for a higher-resolution 1080p set. And funnily enough, this is a question that's still relevant today.

Eventually, of course, manufacturers will completely phase out 720p TVs. But it may take a few years. While the number of new 720p models is dwindling, manufacturers including Sony, Samsung, LG and Panasonic are putting out entry-level 720p TVs in 2009. Correspondingly, we're getting a lot of readers asking whether they should save some dough and buy them. With that in mind, here's the word on 720p vs. 1080p, updated for this year.

Clockwise from left: Toshiba 42AV550 (WXGA), Pioneer PDP-LX509A (1080p), LG 42PG60UD (XGA)
(Credit: Toshiba/Pioneer/LG)

1. What's so great about 1080p?
1080p resolution — which equates to 1920x1080 pixels — is the current Holy Grail of HDTV. That's because most 1080p HDTVs are capable of displaying every pixel of the highest-resolution HD broadcasts and Blu-ray movies. They offer more than twice the resolution of the step-down models, which are typically 1366x768 (WXGA), 1280x720 or 1024x768 (XGA). These days, HDTVs with these three lower resolutions are typically called "720p". Nobody wants to remember numbers, and "768p" doesn't really roll off the tongue.

2. How much extra does a 1080p TV cost?
Several few years ago, you had to pay a huge premium to get a 1080p model at the same screen size as an HD-ready set. While the gap has certainly narrowed, there's still a notable difference. In the case of a 32-inch LCD, for instance, you're looking at around an AU$500 to AU$1,000 price bump. For example, the Sharp LC32D53X goes for AU$1,399, while the step-up 1080p version, the LC32D77X, retails for AU$1,999.

As you move up the LCD size chain, your 720p options become more limited because vendors are going with 1080p displays in most LCDs larger than 37 inches. When it comes to plasma, Panasonic's entry-level 42-inch TH-42PX8A carries a price of around AU$1,699, while the step-up 1080p version, the TH-42PZ80A, comes in at AU$2,549. Move up to 50-inch 1080p models and you're looking at AU$3,649.

3. Why is 1080p theoretically better than 1080i?
1080i, the former king of the HDTV hill, actually boasts an identical 1920x1080 resolution, but conveys the images in an interlaced format (the "i" in 1080i). In a CRT, 1080i sources get rendered on-screen sequentially: the odd-numbered lines of the image appear first followed by even lines, all within 1/25 of a second. Progressive-scan formats such as 480p, 720p and 1080p convey all the lines sequentially in a single pass, which makes for smoother, cleaner visuals, especially with sports and other motion-intensive content.

As a flat screen television is naturally progressive (see below), it will automatically upconvert a 1080i signal to a 1080p picture, and so there may not be an appreciable quality difference on some screens.

4. What content is available in 1080p?
Today's high-def broadcasts are done in either 1080i or 720p, and there's little or no chance they'll jump to 1080p anytime soon because of bandwidth issues. As for HD gaming, Xbox 360 and PlayStation 3 games are available in both 720p and 1080p resolutions. (Also, the 720p titles can be upscaled to 1080i or 1080p in the user settings of those consoles).

Really, the main way to get true 1080p output — aside from hooking your PC to your HDTV — is to get a Blu-ray player. All Blu-ray players support 1080p output. More importantly, the vast majority of movie discs are natively encoded in 1080p.

5. What kinds of TV technologies offer 1080p resolution?
Aside from CRT, which has basically been discontinued, every technology on the market comes in 1080p versions. That means you can find 1080p-capable versions utilising all fixed-pixel technologies, including DLP, LCoS and LCD projectors, and flat panels (plasma and LCD). Of course, as specified above, more affordable entry-level models are still limited to 720p resolution. But whatever the resolution, all fixed-pixel TVs are essentially progressive-scan technologies. So when the incoming source is interlaced (1080i or even good old-fashioned 480i standard definition), they convert it to progressive-scan for display.

At this point, we could just expand on that last point and specify that all fixed-pixel screens always display video at their native resolution. The process of converting resolution is called scaling — or sometimes called upconverting or down-converting. A related factor is deinterlacing (see point number 8, below). How well a TV does (or does not handle) these processes is a big factor in how desirable it is — and something that casual shoppers often overlook since, compared to the screen size or resolution, it's not as easy to show as a spec sheet bullet point.

This whole previous paragraph should probably be put in bold though, because the message never seems to get through. So, at the risk of overkill, let's restate it with specific resolutions.

6. What happens when you feed a 1080i signal to a 720p TV?
The 1080i signal is deinterlaced, then scaled (down-converted) to 720p. Nearly all recent HDTVs are able to do this.

7. What happens when you feed a 1080p signal to 720p TV?
Assuming the TV can accept a 1080p signal, it will be scaled to 720p. But the caveat is that many older 720p and even some 1080p models cannot handle 1080p signals at all. In which case, you'll get a blank screen. Thankfully, most newer HDTVs can accept 1080p signals.

8. What happens when you feed a 1080i signal to a 1080p TV?
It's converted to 1080p with no resolution conversion. Instead, the 1080i signal is deinterlaced for display in 1080p. Some HDTVs perform a better job of this deinterlacing process than others, but usually the artefacts caused by improper deinterlacing are difficult for most viewers to spot.

9. Side by side, how do 720p and 1080p TVs match up in head-to-head tests?
We spend a lot of time looking at a variety of source material on many TVs in our labs. Over three years ago, many 1080p TVs weren't as sharp as they claimed to be on paper. By that, we mean a lot of older 1080p sets couldn't necessarily display all 2 million-plus pixels in the real world — technically, speaking, they couldn't "resolve" every line of a 1080i or 1080p test pattern.

That's changed in the last few years. Virtually all 1080p sets are now capable of fully resolving these materials, though not every 1080p TV is created equal. As our resident video guru, senior editor David Katzmaier, explains, Blu-ray serves up 1080p24 video format which not every TV can display properly. The 24 refers to the true frame rate of film-based content, and displaying it in its native format is supposed to give you a picture exactly as the director intended you to see it.

Whether you're dealing with 1080p24 or video-based 1080p50 doesn't alter our overall views about 1080p TVs. We still believe that when you're dealing with TVs 50 inches and smaller, the added resolution has only a very minor impact on picture quality. In our tests, we put 720p next to 1080p sets, then feed them both the same source material from high-end Blu-ray players. We typically watch both sets for a while, with eyes darting back and forth between the two to look for differences in the most-detailed sections such as hair, textures of fabric, and grassy plains.

Bottom line: it's almost always very difficult to see any difference — especially from farther than 2m away on a 50-inch TV.

The fact is, resolution is resolution, and whether you're looking at a Sony or a TCL, 1080p resolution (which relates to picture sharpness) is the same and is a separate issue from black levels and colour accuracy.

Katzmaier stands by his previous analysis: the extra sharpness afforded by the 1080p televisions he's seen is noticeable only when watching 1080i/1080p sources on larger screens, say 55 inches and bigger and projectors that display wall-size pictures. Katzmaier also adds that the main real-world advantage of 1080p is not the extra sharpness you'll be seeing, but instead the smaller, more densely packed pixels. In other words, you can sit closer to a 1080p television and not notice any pixel structure such as stair-stepping along diagonal lines or the screen-door effect (where you can actually see the space between the pixels). This advantage applies regardless of the quality of the source.

10. Should I save some dough and opt for a 720p TV?
If you're just making the leap to HDTV and find the higher-end sets out of your price range, you shouldn't feel bad about going with an entry-level 720p model (just getting HD programming is going to make a huge difference). Also, in a lot of cases, folks are looking at 720p TVs as second sets for bedrooms or playrooms, and in a tough economy, a few hundred bucks make a big difference.

Finally, it's a good idea to go with 1080p instead of 720p if you plan to use your TV a lot as a big computer monitor. That said, if you set your computer to output at 1920x1080, you might find that the icons and text on the screen are too small to view from far away (as a result, you may end up zooming the desktop or even changing to a lower resolution). But a 1080p set does give you some added flexibility (and sharpness) when it comes to computer connectivity.

If none of those factors jump out at you as true priorities — and you're working on a tight budget and want to save some dough — a 720p set is going to do you just fine. HD will still look great on your set, I swear.