Information on HDTV Resolutions
Putting the High Def into HDTV
In this section of our HDTV shopping guide, we'll examine resolution: that's the format that makes the pictures so clear in HDTV. Get an idea of what the numbers mean before you're standing in the big box store getting tutored in HDTV resolutions by little Billy.
One of the obvious features of high definition television is the enhanced resolution it offers. Presenting the viewer with more pixels is primarily makes the difference between an HDTV and the standard TV you've been watching most of your life. A high definition TV has more pixels so it's able to present more detail in a frame. This is particularly pronounced when looking at background details which on a standard TV will appear jumbled and undefined. HDTV is particularly good at presenting crisp detail in a panoramic view. The exact number of pixels your new HDTV is capable of presenting is called the TV's native resolution. Understanding the formats of television will enable you to understand the display technologies used to create images.
480i: This the broadcast standard outlined by the NTSC in North America. Sometimes 480i is simply called NTSC or SDTV, but the terms are practically interchangeable. This refers to the old way pictures were displayed on CRT (Cathode Ray Tubes or picture tubes) for decades.
The CRT creates pictures with scan lines that are basically a series of horizontal lines stacked on top of each other to comprise a single frame. These lines are interlaced, which means you only see every 'other' line at any one time. At one instant you'll see every even numbered line and then in the very next you'll see the odd numbered lines. The alternating interlaced lines switch so quickly that we don't notice. The refresh rate or fps, which stands for frames or fields per second, is 60 cycles per second to be exact.
When your set is designated 480i, as all older TVs are, it has 480 visible lines of resolution interlaced so they cycle between odd and even lines at a rate of 60 fps. This is how your old uncle Ralph grew up watching I Love Lucy and how you used to watch reruns of Gilligan's Island.
480P: The first trick performed by advanced television engineering to improve image quality was to de-interlace the images. That is, to display all the horizontal lines at one time (or in one sweep) instead of having them alternate between odd and even numbers. This format is visibly better than standard definition TV at 480i.
- Most EDTV (Enhanced Definition TVs) can display 480P, but not much more than that
- If you have an HDTV and watch a DVD through component cables (in progressive scan), you're watching it in 480P
720P: At the 720P designation we have entered true HDTV. Just as 480i is displayed by CRT display technology, 720P is displayed on a fixed pixel display technology like LCD or Plasma. These display types don't use scan lines, rather they present a matrix of pixels. What makes it high definition is that instead of 480 lines there are 720 lines that comprise the picture.
The 720P format can actually be given a resolution in ## of pixels by ## of pixels which is usually 1280 x 720. Sometimes the native resolution can be a bit more. For instance, it's not uncommon to find an HDTV at 1280 x 760 or 768. Most computers have a common resolution called 1024 x 768, which is very similar to 720P. However, a TV that advertises a native resolution of 1024 x 720 (or 1024 x 768) is not a true HDTV. In fact, it's only an EDTV. EDTV offers a low budget alternative to true HDTV. EDTV is a set capable of progressive scan, but does not offer true HD resolutions. Either way, EDTV's are sold at slightly lower prices than true HDTV. It's probably not a good idea to save money by buying an EDTV. The difference in image quality is noticeable and any savings you'll get from EDTV will be recovered if you simply wait a few months before buying a real HDTV.
1080i: The next HDTV format is 1080i, which is the CRT's equivalent of a 720P image. The two formats are about equal in relative picture quality. Since CRT based display types use scan lines as explained in 480i, the native resolution for a CRT based HDTV becomes 1080i.
1080P: Some expensive sets today can produce images that are 1080P. The trouble with 1080P is that many are only displaying 1080P images at 30 frames per second. All the above formats are safely assumed to be presented at 50 or 60 fps. This is not so with 1080P. 1080P is generally seen as a way for affluent buyers to avoid purchasing a TV that isn't capable of displaying an even newer format. At this time there is no source material that is capable of displaying 1080P. It's too early to tell if HD DVD or Blu-ray media will be available as a 1080P / 60 source for this new and untested format. It is unlikely that broadcasters will embrace the 1080P format any time soon as most have only recently upgraded cameras and transmission equipment to facilitate 720P at great cost.
- CRT based HDTVs use interlaced scan lines to produce a native resolution of 1080i
- LCD (Liquid Crystal Display), Plasma, DLP (Digital Light Processing) are examples of fixed pixel display types
- Fixed pixel display types do not use scan lines so they display a progressive resolution similar to a computer in a fixed matrix of pixels
- 1080i and 720P are accepted formats for HDTV, anything less is designated as EDTV
- Standard TV is only capable of 480i
- EDTV is capable of 480P or any other resolution that falls short of a true 1280x720 resolution
Another important attribute to understanding HDTV before you buy is Aspect Ratio.