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What is the Difference Between 1080p and 1080i, and Does It Matter?
Last Updated on Tuesday, November 20th, 2007 1:38 PM
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With the introduction of the HD DVD and Blu-ray high definition disc formats, as well as HDTV's that are capable of HDTV's highest resolution of 1920x1080, the terms 1080i and 1080p are being thrown around much more than ever before.
The big difference in the terms, of course, is the i (for interlaced) and p (for progressive), which indicate how the image is stored and how it is displayed.
In the analog world of televisions, interlaced vs. progressively scanned video was an important distinction. Interlacing involves showing every other line of video in one frame and then supplying the remaining lines on the next pass. Standard analog television signals are interlaced by necessity, because standard analog TV's were never designed to handle anything but an interlaced signal.
New HDTV's are inherently progressively scanned devices. Their circuitry displays video all at once, so if they receive interlaced signals, those signals are de-interlaced to progressive signals before they are displayed. Until recently, few HDTV's could accept a 1080p signal due to cost savings or other technical limitations. HDTV's capable of only the lower 1280x720 HDTV resolution will usually only accept interlaced video at the higher 1920x1080 resolution.
Both HD DVD and Blu-ray store movie-based video on the discs in 1080p at 24 frames per second (fps). Some players do not output 1080p, but rather 1080i due to the circuitry implemented in the player for cost-savings or product maturity reasons.
Most displays are not capable of accepting a 1080p signal at 24 frames per second. More than likely, they need a 1080p signal at 60 frames per second (if they can take 1080p at all), so the conversion from 24 fps to 60 fps still needs to happen somewhere (this conversion is called 3:2, or 2:3, pulldown). The fact that most TV's cannot handle 1080p24 is why most HD DVD players and Blu-ray players alike output 1920x1080 at 60 fps in either interlaced or progressive fashion.
Does this mean that you're losing picture quality if your player is outputting 1080i, or your TV is only capable of accepting 1080i? As long as your TV is capable of displaying 1920x1080 pixels on the screen, and its internal circuitry was designed properly, there won't be any difference between a 1080i and 1080p input. The HDTV will deinterlace the 1080i signal, create a 1080p signal from it, and then display it to you. Unlike in the old days of analog video, there is no information lost or artifacts introduced as a result of the deinterlacing process. All the information is there, it just has to be reassembled.
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Our recommendation? Don't overspend for the ability to output 1080p vs 1080i from an HD DVD or Blu-ray player (although the addition of 1080p output brings along other features which may be worth the upgrade to a model that sports it.) Unless your display can display 1920x1080 progressive at 24 frames per second (or a multiple of 24, like 48, 72, or 120), you do not need to spend the extra money on players that provide 1080p output. Such displays are beginning to appear on the market, but are not common.
Rather, put that money towards a high quality display that can do 1920x1080 well. A decent HDTV will be able to deinterlace the 1080i signal you give it and you will be able to enjoy all the pixels that the HD formats can provide. If you are looking for a new display, buy one that can handle 1080p24 natively. They are going to be expensive and most likely a little hard to find, so whether the extra expense is worth it to you is for you to decide.
If you can't justify the price increase from a 720p capable display, don't worry. These formats look great on those as well!
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