Explaining HDTV Video Resolution (480i, 480p, 720p, 1080i, 1080p and beyond)
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By Adrienne Maxwell
Sure, you've heard about high-definition television. Maybe you've even seen it demoed at your local retailer. You know that it looks better than standard-definition, but, beyond that, you're stumped. Why does it look better? What exactly is the difference between standard- and high-definition? And what do all those resolution terms - 480i, 720p, 1080i, and 1080p - mean?
In the simplest terms, a 480i signal is standard-definition, while 720p, 1080i, and 1080p are all high-definition resolutions. As you can see, each resolution is made up of two parts: a number (480, 720, 1080) and a letter (i or p). The number refers to how much detail the signal has, while the letter refers to the way the signal is transmitted and/or displayed on the TV screen.
On the letter side, "i" stands for interlaced. When broadcast TV was first born, the architects decided to break up the signal in order to reduce its transmission size. Rather than show each frame as one full image, they split the frame into two fields, first showing the odd lines and then the even ones. This happens so quickly, your eyes automatically stitch the two fields together to form the complete image in your brain. Most standard-definition TV channels and some high-def ones like NBC HD and CBS HD still broadcast in this interlaced manner. Old analog TVs and some first-generation HDTVs display signals in an interlaced form as well.
Most new HDTVs and many high-def channels have abandoned the "i" for the "p," which stands for progressive. In a progressive signal, the complete frame is transmitted and displayed at once, with no splitting into separate fields. ABC, Fox, and ESPN broadcast their HD channels in progressive form, and digital TV technologies like plasma, LCD, DLP, and LCOS are progressive by design. Displaying an interlaced signal on a progressive TV requires that the TV or source device stitch the interlaced fields back together to show the complete frame. When this is done properly, an interlaced image will look just as detailed as a progressive one. However, many people contend that progressive signals have smoother, cleaner motion on a progressive TV because no extra processing steps are required.
As for the number in each resolution term, it refers to the signal's vertical resolution, or how many rows of pixels make up the image. (Yes, the rows are horizontal; however, to count them, you would move along the vertical axis, thus the term "vertical resolution.") The higher the number, the more rows there are: a 480i signal has 480 rows of pixels, 720p has 720 rows of pixels, and so on. More rows equal more detail. You may also see resolution listed in the form "1,280 x 720," which tells you the number of columns by the number of rows. This is actually a more complete description, as it allows you to calculate the image or screen's exact number of pixels: 1,280 x 720 = 921,600 pixels.
Here's a quick breakdown of each resolution type:
480i: Basic cable, satellite and DVD signals have a 480i resolution, which means the signal is separated into two fields containing 240 rows. DVD has a higher horizontal resolution (more columns of pixels) than cable and satellite SDTV signals, so it has better overall detail. DVD resolution is 720 x 480, for a total of 345,600 pixels.
720p: Broadcasters like ABC, Fox and ESPN transmit their HD signals in the 720p format. Many early HDTVs and a number of today's entry-level models have a 720p resolution. The exact resolution of these TVs is often 1,280 x 720, or 921,600 pixels
1080i: Broadcasters like CBS, NBC and the CW transmit their HD signals in the 1080i format, which means the signal is separated into two fields containing 540 rows. We should note that, when the two fields are stitched together properly, a 1080i signal has the same resolution as a 1080p signal: 1,920 x 1,080, or 2,073,600 pixels. However, there's a greater chance of motion artifacts and other processing errors when dealing with 1080i.
1080p: This is currently the highest resolution available for most consumer HDTVs and source devices. A majority of new HDTVs, especially the more expensive ones, have a 1080p resolution. The exact resolution is 1,920 x 1,080, or 2,073,600 pixels. Blu-ray discs generally have a 1080p resolution. No broadcasters currently transmit TV signals in the 1080p format; however, satellite and cable providers occasionally make on-demand movies available at a 1080p resolution.
Higher Resolutions: Resolutions beyond 1080p are available in the high-end projector realm; companies like Sony and JVC offer projectors with a resolution of 4,096 x 2,160. As for TVs, we've seen many demos at trade shows of HDTVs with higher resolutions, such as 1440p and 2160p. These currently suit applications in the commercial realm, but have yet to materialize as real-world consumer products.
Keywords
High definition, standard definition, 480i, 720p, 1080i, 1080p, interlaced, frame, field, progressive, plasma, LCD, DLP, LCOS, vertical resolution, pixels, 720 x 480, 1,280 x 720, 1,920 x 1,080, Blu-ray, on-demand, 1440p, 2160p
