Technically, ther are 18 different standards for digital TV broadcasting (all Digital TV tuners are required to decode all 18 standards), the practical application of DTV has come down to 3 standards. These standards are: 480p, 720p, and 1080p as picture shown below:
480p
If you have a progressive scan DVD player and TV, you are familiar with 480p (480 lines of resolution, scanned progressively). 480p is similar to the same resolution of standard broadcast TV (and is referred to as SDTV or Standard Definition Television), but the image is scanned progressively, rather than in alternate fields.
480p does provide an excellent picture (especially on smaller 20-27" screens). It is much more film-like than standard cable or even standard DVD output, but it only provides half the potential video quality of an HDTV picture, therefore its effectiveness is lost on larger screen sets. Although 480p is part of the approved DTV broadcasting scheme, it is not HDTV. This standard was included as one of the DTV broadcasting standards to provide broadcasters the option of providing multiple channels of programming in the same bandwidth as a single HDTV signal. In other words, 480p is just more of what we already have with only a slight increase in image quality.
720p
720p (720 lines of resolution scanned progressively) is also a digital TV format, but it is also considered as one of the HDTV standards. As such, ABC, and now FOX, have committed to 720p as their HDTV broadcasting standard. Not only does 720p provide a very smooth, film-like image due to its progressive scan formula, but image detail is at least 30% sharper than 480p. As a result, 720p provides an acceptable image upgrade that is visible on both medium (32"- 36") size screens as well as larger screen sets. Also, even pthough 720p is considered high-definition, it takes up less bandwidth than 1080p, which is covered next.
1080p
In the last couple of years, there has been a big influx of HDTVs with 1080p native resolution, which typically cost a good deal more than their lower-resolution counterparts. But as we've been saying all along, once you get to high-def, the difference between resolutions becomes much more difficult to appreciate. We've done side-by-side tests between two 46-inch LCD HDTVs, one with 1366x768 resolution and the other with 1080p resolution, using the same 1080i source material, and it was extremely difficult for us to see any difference. It becomes even more difficult at smaller screen sizes or farther seating distances--say, more than 1.5 times the diagonal measurement of the screen. We've reviewed a 37-inch 1080p LCD, for example, where it was impossible to see the separation between horizontal lines at farther than 45 inches away.
The 10870p technically do deliver more detail, which can enhance the viewing experience for more eagle-eyed viewers. Also, many manufacturers build other picture-quality benefits, such as better contrast and/or color, into their 1080p HDTVs simply because those sets are the high-end models. And given the continuing march of technology, we expect more and more 1080p models to become available at lower and lower prices. Today, however, the premium for 1080p is still pretty steep, and unless you're getting a very large set, say 50 inches or more, we don't recommend basing a buying decision on whether or not the television has 1080p native resolution.
HDTV source resolutions
If you read those three axioms closely, you'll see that source is everything with HDTV. Or, as some unknown wag once said, "Garbage in, garbage out." There are two main HD resolutions in use today by HD broadcasters and other sources: 1080i and 720p. One is not necessarily better than the other; 1080i has more lines and pixels, but 720p is a progressive-scan format that should deliver a smoother image that stays sharper during motion. Another format is also becoming better known: 1080p, which combines the superior resolution of 1080i with the progressive-scan smoothness of 720p. True 1080p content is extremely scarce, however, and none of the major networks have announced 1080p broadcasts. The term 1080p today appears mostly in reference to the displays' native resolution, not the source.
| Source resolution name | Resolution in pixels | HDTV? | Progressive-scan? | Wide-screen? | Networks/sources |
| 1080p | 1,920x1,080 | Yes | Yes | Yes | Blu-ray and future HD-DVD players; PlayStation 3 |
| 1080i | 1,920x1,080 | Yes | No | Yes | Includes CBS, NBC, PBS, DiscoveryHD,Xbox 360 |
| 720p | 1,280x720 | Yes | Yes | Yes | ABC, Fox, ESPNHD |
| 480p | 852x480 | No | Yes | Yes | Fox wide-screen; progressive-scan DVD players, Wii |
| Regular TV | Up to 480 lines | No | No | No | All |
What is the Difference Between Standard Definition, Enhanced Definition and High Definition TV?
What we call high definition TV is just one type of digital television. All HDTV is digital, but not all digital TV is high definition. In fact, there are three primary types of digital television: standard definition (SDTV), enhanced definition (EDTV) and high definition (HDTV). And within HDTV, there are several variations, each with a different picture resolution. It's all a bit confusing, so settle back for a quick explanation.
Analog vs. Digital
Until very recently, all television broadcasts were analog. With analog transmission, programming is transmitted in a continuous signal that varies in amplitude, depending on the information contained in the picture. This signal can easily deteriorate over distance or suffer interference from other sources, which produces a lower-quality picture than the original. The primary advantage of digital transmission is that it slices the traditional analog television signal into a series of digital bits, which are then recombined to reproduce an exact copy of the original broadcast. These digital signals don't weaken with distance, as analog signals do. As long as the signal can be received, the picture is perfect, with no degradation. Since digital signals are comprised of binary bits, a 1 is always a 1 and a 0 is always a 0. Because of this exact end-to-end reproduction, digital means better picture and sound quality, no matter what is broadcast.
Different Types of Digital TV
Digital programming comes in many shapes and sizes. Not all digital broadcasts have the same resolution or aspect ratio. Here's a quick guide to all current digital formats:
• SDTV - Standard definition digital television has the same resolution and 4:3 aspect ratio as traditional analog television but is transmitted in digital fashion. The SDTV picture is 480 x 640 pixels, with interlaced scanning.
• EDTV - Enhanced definition television has the same resolution as SDTV but with progressive scanning instead of interlaced scanning, which creates a smoother overall picture. EDTV can be in either the 4:3 or 16:9 aspect ratio, for a resolution of either 480 x 640 or 480 x 720 pixels.
• HDTV (720p) - The first of the three current high definition television formats features 720 x 1280 pixel resolution with progressive scanning. This format is ideal for programming with lots of movement, such as sporting events. The aspect ratio is 16:9.
• HDTV (1080i). The second current high definition format features greater resolution than 720p (1080 x 1920 pixels), but with interlaced scanning. Like 720p, the aspect ratio is 16:9
• HDTV (1080p) - This is the ultimate high definition format, with 1080 x 1920 pixel resolution (in the 16:9 ratio) and progressive scanning. Because of the high bandwidth requirements, this format is not yet used for television broadcasts, although the new HD DVD and Blu-ray high-definition DVD formats will be capable of a 1080p picture.
Comparing the Formats
So which formats are used where? The following table provides a brief rundown of all the digital formats, as well as our current NTSC analog format:
| | NTSC | SDTV | EDTV | EDTV | HDTV | HDTV | HDTV |
| Description |
480i (analog) | 480i (digital) | 480p | 480p (widescreen) | 720p | 1080i | 1080p |
| Transmission type |
Analog | Digital | Digital | Digital | Digital | Digital | Digital |
| Aspect ratio |
4:3 | 4:3 | 4:3 | 16:9 | 16:9 | 16:9 | 16:9 |
| Picture height (pixels) |
480 | 480 | 480 | 480 | 720 | 1080 | 1080 |
| Picture width (pixels) |
640 | 640 | 640 | 720 | 1280 | 1920 | 1920 |
| Total number of pixels |
307,200 | 307,200 | 307,200 | 345,600 | 921,600 | 2,073,600 | 2,073,600 |
| Scanning |
Interlaced | Interlaced | Progressive | Progressive | Progressive | Interlaced | Progressive |
| Used by |
Standard broadcast television | DVD, direct broadcast satellite, digital cable | Progressive-scan DVD | Progressive-scan DVD | HD broadcasts (ABC, ESPN, Fox) | HD broadcasts (CBS, CW, DiscoveryHD, HBO, HDNet, NBC, PBS, Showtime) | Not yet in use for broadcast TV; used in HD DVD and Blu-ray high definition DVDs |
|
