High definition television (HDTV) is the highest form of digital television. It has a 16:9 aspect ratio, which is similar in appearance to a movie theater screen. HDTV has a couple of advantages over the old analog TV format -- the wide screen and the resolution.
The wide screen is good on our eyes -- we see the rectangular wide screen images better than the old square format. Basically, our eyes see better from left/right compared to up/down. The wide screen will also let us see more of the on-screen scene, which is great for sports and movies.
Resolution is undoubtedly HDTVs biggest selling point. HDTV's resolutions are 720p, 1080i and 1080p -- the number stands for the number of lines that create the image and the letter describes the type of scan used by the TV to display the picture.
Resolution matters because the more lines means a better picture. This is a similar concept to digital photos and how dpi determines print quality.
Resolution is the main reason why HDTV looks so much better than standard television. On a high-definition TV displaying a high-definition source, a million or more pixels combine to create images that appear sharper and more realistic than TV ever has before. Resolution isn't the be-all and end-all of picture quality, however, and its numerous, well, numbers, can be incredibly intimidating at first. In this article we'll try to demystify HDTV resolution and help you cut through the hype that surrounds all of those numbers.
How important is resolution?
Although resolution separates HDTV from standard-definition TV, it's not as important to overall picture quality as other factors. According to the Imaging Science Foundation, a group that consults for home-theater manufacturers and trains professional video calibrators, the most important aspect of picture quality is contrast ratio the second most important is color saturation, and the third is color accuracy. Resolution comes in fourth, despite being the most-cited HDTV specification.
Source resolution name | Resolution in pixels | HDTV? | Progressive- scan? | Wide- screen? | Networks / sources |
1080p | 1,920x1,080 | Yes | Yes | Yes | Blu-ray players; PlayStation 3 and Xbox 360; some video-on-demand sources like Vudu |
1080i | 1,920x1,080 | Yes | No | Yes | Includes CBS, NBC, PBS, DiscoveryHD Theater |
720p | 1,280x720 | Yes | Yes | Yes | Includes ABC, Fox, ESPNHD |
480p | 852x480 | No | Yes | Yes | Progressive-scan DVD players |
480i | Up to 480 lines | No | No | No | All standard-definition TV broadcasts |
Which HDTV Format Is Better -- 720p, 1080i, and 1080p?
To put the 720 or 1080 lines into perspective, televisions of the past had 480 lines. Since more lines means a better picture then that alone shows why the HDTV has a nicer picture than an analog TV.
More lines is nice but don't forget about the 'p' and 'i' in the 720p, 1080i and 1080p. The letter is an abbreviation for the type of scan the TV uses -- 'p' stands for progressive and 'i' stands for interlaced.
Progressive scan is better than interlaced because it processes the images twice as fast. This faster scan rate produces better clarity and color in the on-screen picture.
The difference between 720p and 1080i is minimal but the TV industry is using 720p more than 1080i. So, buying a 720p HDTV is recommended over a 1080i HDTV.
As far as 1080p, there is no doubt that 1080p is the best resolution on the market. However, there is little to no difference in picture quality between a 1080p and 720p at the 32" and below screen size.
The truth about 1080p
In the last couple of years, HDTVs with 1080p native resolution have taken over the market at nearly every price and size point. But as we've been saying all along, once you get to high-definition, the difference between resolutions becomes much more difficult to appreciate. We've done numerous side-by-side tests between two same-size HDTVs, one with 1080p resolution and another with lower resolution, and every time it's been almost impossible to see the difference with regular program material, especially when that material is moving. The difference becomes even more difficult to see at smaller screen sizes or farther seating distances--say, more than 1.5 times the diagonal measurement of the screen. For example, to see the benefits of stationary 1080p content on a 50-inch screen, you'll generally need to sit about 6.5 feet or closer. Few viewers want to sit that close, especially when low-quality content seen at that distance (remember the "garbage" maxim?) looks so bad. The main visible benefit of 1080p native resolution comes when the display is asked to show computer sources. With a PC set to output 1080p resolution and a 1080p display that can accept it, computer desktops and text generally look superb, and quite a bit better than when displayed on a TV with lower native resolution. But for movies, games, and other standard video material, the benefits of 1080p are negligible unless you're sitting quite close. That doesn't matter much anymore though. 1080p native resolution is so common among HDTVs, and has so little impact, that you shouldn't even consider it as a factor in your purchasing decision. As we mentioned at the top, factors like contrast and color are more important to image quality, and unfortunately, you can't depend on a specification sheet for an accurate representation of those factors.
More mixed signals: 1080p/60 versus 1080p/24
1080p HDTVs are a dime a dozen, but not all 1080p HDTVs are created equal. First off, some older HDTVs with 1080p resolution couldn't accept 1080p sources at all. More recently, the advent of Blu-ray has delivered another video format variation to worry about: 1080p/24.
The numbers 24 and 60 refer to frame rate. Moving video is composed of a certain number of frames transmitted every second that combine in the viewer's mind to create the illusion of movement. The nominal rate for film is 24 frames per second, while the rate for video is 30 frames per second. In standard 1080p video, which is technically 1080p/60, each frame is repeated twice. Every 1080p HDTV sold today can accept and display 1080p/60 sources via its HDMI inputs.
Not every 1080p HDTV properly displays 1080p/24 sources, however. Most Blu-ray players, as well as the PlayStation 3, have a setting that lets the player transmit 1080p/24 video directly. Blu-ray Discs with movies that originate on film are encoded at 1080p/24 to preserve the proper cadence of film--that characteristic motion that's smooth but not too smooth. If your player is set to output 1080p/24 directly, and your TV can properly display it, you're seeing the image as close as possible to what the director intended--how it looks when displayed on a cinema screen from a film projector at your local movie theater.
Generally, for an HDTV to properly display 1080p/24 it needs to have a refresh rate at some multiple of 24. The standard refresh rate for HDTVs of all varieties is 60Hz, which is not a multiple of 24. There's no benefit to sending these displays 1080p/24 instead of 1080p/60. If the HDTV can actually show the signal (some cannot), the result usually looks the same regardless of the setting on your Blu-ray player.
On the other hand, increasing numbers of LCD TVs have refresh rates of 120Hz or 240Hz, for example, while a few plasmas refresh at 48Hz, 72Hz, or 96Hz. All are exact multiples of 24. Some of these HDTVs come closer to preserving the cadence of film than others, and some can introduce extra dejudder video processing (usually user defeatable) that also affects cadence. Unlike with resolution, there's no easy way to tell from the spec sheet if a display with a multiple of 24 as its refresh rate handles 1080p/24 correctly, although most such displays that we've tested do.
For most viewers the visible benefits of 1080p/24 are slight. Displays that cannot show it correctly can nonetheless produce a viable semblance of film's cadence, one that to experienced viewers appears to stutter slightly, especially in pans or camera movement, instead of move more smoothly like true film cadence. But for purists interested in seeing every last benefit of film, 1080p/24 signals mated to a 1080p/24-compatible display are worth the investment.
The numbers 24 and 60 refer to frame rate. Moving video is composed of a certain number of frames transmitted every second that combine in the viewer's mind to create the illusion of movement. The nominal rate for film is 24 frames per second, while the rate for video is 30 frames per second. In standard 1080p video, which is technically 1080p/60, each frame is repeated twice. Every 1080p HDTV sold today can accept and display 1080p/60 sources via its HDMI inputs.
Not every 1080p HDTV properly displays 1080p/24 sources, however. Most Blu-ray players, as well as the PlayStation 3, have a setting that lets the player transmit 1080p/24 video directly. Blu-ray Discs with movies that originate on film are encoded at 1080p/24 to preserve the proper cadence of film--that characteristic motion that's smooth but not too smooth. If your player is set to output 1080p/24 directly, and your TV can properly display it, you're seeing the image as close as possible to what the director intended--how it looks when displayed on a cinema screen from a film projector at your local movie theater.
Generally, for an HDTV to properly display 1080p/24 it needs to have a refresh rate at some multiple of 24. The standard refresh rate for HDTVs of all varieties is 60Hz, which is not a multiple of 24. There's no benefit to sending these displays 1080p/24 instead of 1080p/60. If the HDTV can actually show the signal (some cannot), the result usually looks the same regardless of the setting on your Blu-ray player.
On the other hand, increasing numbers of LCD TVs have refresh rates of 120Hz or 240Hz, for example, while a few plasmas refresh at 48Hz, 72Hz, or 96Hz. All are exact multiples of 24. Some of these HDTVs come closer to preserving the cadence of film than others, and some can introduce extra dejudder video processing (usually user defeatable) that also affects cadence. Unlike with resolution, there's no easy way to tell from the spec sheet if a display with a multiple of 24 as its refresh rate handles 1080p/24 correctly, although most such displays that we've tested do.
For most viewers the visible benefits of 1080p/24 are slight. Displays that cannot show it correctly can nonetheless produce a viable semblance of film's cadence, one that to experienced viewers appears to stutter slightly, especially in pans or camera movement, instead of move more smoothly like true film cadence. But for purists interested in seeing every last benefit of film, 1080p/24 signals mated to a 1080p/24-compatible display are worth the investment.
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