Is there a limit to how high-definition TVs can get?

HDTV Image Gallery Every year at CES, manufacturers like Panasonic try to push the limits of HDTV. See more HDTV pictures.
AP Photo/Mark Lennihan

Imagine that you have two copies of a movie and two television sets. One copy is on Blu-ray and you pair that with a high-definition television -- an HDTV. The other copy is on standard DVD, which you'll watch on a standard-definition television. You synchronize both videos and watch the results.

The difference in image quality between the two sets should be obvious. The HDTV's picture should look crisper and have colors far more vibrant than the standard counterpart. We've reached the peak of video quality -- or have we?

When we talk about HDTVs, we're really talking about image resolution. The picture on a television set is composed of millions of tiny dots of light called pixels. Standard-definition televisions have a resolution of 480. That means approximately 480 horizontal lines from the top of the screen to the bottom generate the images you see.

High-definition televisions pack more lines of pixels to create images. On the low end of the high-definition standard in the United States you have approximately 720 lines of pixels. On the high end, you have approximately 1,080 lines of pixels. Manufacturers are slowly phasing out the 720-line models in favor of the 1,080-line ones.

Using more pixels to create an image results in a smoother picture. Imagine you're given a stack of green and brown squares of paper. You're told you have to build a picture of a tree using the squares exactly as they are. If the squares of paper are large, your tree is going to look blocky with lots of jagged edges. But if you have smaller squares of paper, the tree will look smoother and more natural.

That's what high-definition television does. It's not just the number of pixels in the image -- it's the size of each individual pixel. As you pack more pixels into a screen, you have to make the pixels themselves smaller. In turn, the television will produce smoother images.

But is 1080 the best resolution possible? Could you buy a television set that packed even more pixels together? Would it make a difference? And would you be able to find programming that conformed to the higher resolution? Let's find out.

Packing Pixels on HDTV Screens

Currently, the highest resolution television you can buy in the United States is 1080 lines. That's not because we've hit a physical limit on how many pixels we can pack into a screen. It has more to do with the HDTV standard. While many high-definition televisions can upconvert standard signals to fit the screen's resolution, true high-definition content is necessary for the full experience.

You can get high-definition video from certain cable or satellite services, a Blu-ray or HD-DVD player or one of a dozen other devices like the PlayStation 3 or Xbox 360. This content should look crisper than upconverted standard-definition content on an HDTV. If a manufacturer offered a set that fit more pixels on the screen, you wouldn't really be able to take advantage of it. You need that infrastructure of content providers to see pictures in a higher resolution.

With smaller screens, a higher resolution may be a waste. That's because the number of pixels in HDTVs remains constant no matter the size of the screen. It's a question of pixels versus area. A 720-line HDTV has a picture made up of 1,280 vertical lines by 720 horizontal lines of pixels. That gives a grand total of 921,600 pixels. A 1080-line HDTV has 1,920 vertical lines by 1,080 horizontal lines. That gives us a grand total of 2,073,600 pixels.

In general, all 1080-line HDTVs have the same number of pixels. Whether your television screen's diagonal measures 26 inches (approximately 66 centimeters) or 55 inches (approximately 140 centimeters), it will still show 2,073,600 pixels. The pixels in the 26-inch model will just be smaller.

But do the smaller pixels make the picture better? If you put a 26-inch HDTV with 720-line resolution next to a 26-inch HDTV with 1080 resolution, you may not be able to tell the difference in resolution. The pixels are already so small at 720-line resolution that making them smaller doesn't help.

On larger screens -- 55 inches (approximately 140 centimeters) or larger -- the 1080-pixel resolution is best. That's because the larger screens use bigger pixels. If the pixels are too big, the image will look jagged or blocky. The distance between the screen and your eyes makes a difference, too. The farther away you are, the smoother the picture will appear.

Enormous Televisions

As televisions get larger, like this 150-inch set from Panasonic, you need more pixels to keep the picture nice and sharp.
As televisions get larger, like this 150-inch set from Panasonic, you need more pixels to keep the picture nice and sharp.
David Paul Morris/Getty Images

As televisions get bigger, we need more pixels to create a smooth image. For most households, 1080-pixel resolution is probably sufficient. But if you have a mansion and you want a 200-inch (508-centimeter) television screen in your den, 1080 just won't cut it. The sad fact is that even if you get a television with an amazing number of pixels, you may not have any content to watch on it.

In the future, we may see ultra-high definition televisions (UHDTVs). While the peak of HDTV in the United States is 1,080 horizontal lines of pixels, the UHDTV standard may be closer to 4,000 lines. A 200-inch television with 4,000 lines of resolution could provide the clear, smooth images you'd want in a piece of equipment that enormous.

Some manufacturers are already producing technology that could create UHDTV content. A camera known as the RED ONE is one example. It can shoot 4,000 lines of resolution at 30 frames per second. The output of the RED ONE isn't necessarily meant for televisions. Instead, filmmakers can use the camera to shoot HD movies for the cinema. In case you're curious, the RED ONE creates images made up of 12,065,000 pixels [source: Red.com].

Again, packing that many pixels into a smaller television wouldn't necessarily create a perceivably better picture. But for giant screens and movie theaters, it's a requirement. You need each pixel to be tiny to create high-definition images.

The limits of HDTV aren't really technologically mandated -- they're biologically dictated. If a human being can't tell the difference between a 26-inch (66-centimeter) picture that has fewer than 1,000,000 pixels and another that has 12,065,000 pixels, there's no point in pushing the technology further. For the average consumer, a 1080-pixel resolution will probably be enough. As is the case with many things in life, more does not always equal better.

Learn more about HDTV technology by following the links on the next page.

Related HowStuffWorks Articles

More Great Links

Sources

  • Alvarez, Salvador et al. "HDTV: The Engineering History." MIT. Dec. 10, 1999. (Sept. 15, 2009) http://web.mit.edu/6.933/www/HDTV.pdf
  • Barlow, Steven. "HDTV Past, Present and Future." Audioholics. July 23, 2009. (Sept. 15, 2009) http://www.audioholics.com/education/display-formats-technology/hdtv-past-present-and-future-part-i-history
  • Carnoy, David. "720p vs. 1080p HDTVs: 2009 update." CNET. March 10, 2009. (Sept. 16, 2009) http://reviews.cnet.com/720p-vs-1080p-hdtv/
  • CEA. "HDTV." 2009. (Sept 16, 2009) http://www.ce.org/Press/CEA_Pubs/928.asp
  • Gordon, Clay. "The guide to high definition video production: preparing for a widescreen world." Focal Press. 1996.
  • Heingartner, Douglas. "Just Like High-Definition TV, but With Higher Definition." The New York Times. June 3, 2004. (Sept. 16, 2009) http://www.nytimes.com/2004/06/03/technology/circuits/03next.html
  • Long, Mark. "The Long and Winding Road: The Future of High Definition Television in Asia." MLE Inc. 1999. (Aug. 14, 2009). http://mlesat.com/Articl15.html
  • Sugawara, Masayuki. "Research on Human Factors in Ultra-high-definition Television to determine its Specifications." NHK's Science and Technical Research Laboratories (Japan Broadcasting Corporation). October 2007. (Sept. 17, 2009) http://www.nhk.or.jp/digital/en/technical/pdf/IBC2007_08040906.pdf