What’s the Difference Between 1080p and 1080i?

High definition television has become a common presence in many homes, and the array of available features can be dizzying. One of the main decisions to make involves screen resolution. Televisions with 1080 pixels have become the standard for the highest quality, yet consumers must also consider how a unit delivers the picture. Sets with 1080i and 1080p designations both have screen resolutions of 1920 x 1080 pixels, but they render pictures differently, resulting in slightly different image quality.


1080i for Interlaced


Televisions with 1080i resolution display each image twice and interlace them to create a full picture. Odd- and even-numbered pixel rows illuminate alternately so that at any given moment, only half the lines display a picture; instead of 1920 x 1080 resolution, the screen shows 1920 x 540. However, each group flashes 30 times per second, combining for a total of 60 frames per second, which is generally too fast for the human eye to detect. All that’s visible is the complete picture.


1080p for Progressive


Televisions with 1080p resolution also display images at 60 frames per second, but they do so in progressive fashion, lighting one pixel line after another. This results in each line refreshing 60 times every second rather than 30, which creates a sharper image. Progressive displays are especially helpful for fast motion; where 1080i can produce noticeable blurring during quick action, 1080p has the faster refresh rate needed for increased clarity. For this reason, 1080p is often called “True HD” or “Full HD.”


Choosing Between 1080i and 1080p


If 1080p creates a better picture, is there any reason to choose 1080i? Cost may be the main factor. The quality difference is far less noticeable on smaller televisions, such as those intended for a kitchen or office, and consumers may decide that it’s not worth paying more for 1080p on sets under 42 inches. Additionally, viewers who don’t watch a lot of action or sports programming may be able to buy a larger 1080i set for less money yet receive perfectly satisfying images. The one caution to note is that viewing distance has a noticeable impact. Because resolution diminishes the closer the viewer is to the screen, 1080p might be the better choice in close settings regardless of television size.


Cable, Broadcast and Blu-ray Factors


Anyone who has watched both Blu-ray discs and HD programs through a cable or satellite provider knows that the broadcasts suffer by comparison; there is a marked reduction in sharpness and detail. This difference occurs because even though televisions can render full 1080 resolution, images delivered through set-top boxes and cable cards aren’t full HD quality.

Signals may only be sent in 1080i to begin with, and companies also typically compress data to stay within bandwidth restrictions. With limited broadcast space, and with consumer demand for multiple HD channels, providers must compress the signals. This inevitably diminishes HD quality, meaning that even 1080p sets sometimes display color irregularities and fuzzy details. It may seem old-fashioned, but using an over-the-air HD antenna and tuning to broadcast HD channels will result in a better picture since the signals aren’t compressed; the flip side is that cable-only HD channels then become unavailable.

With an ultra-fast Internet data connection and new technology that allows wi-fi transmissions from computer to television, streaming video may look better than cable or satellite images, but many viewers would still lose sharpness due to slower speeds. As companies search for ways to deliver true HD programming, for now, Blu-ray is the only format that shows pure 1080p resolution. Even so, the next innovation is probably just around the corner.

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