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1080i/p

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1080i refers to video containing 1080 horizontal lines of resolution, stored in an interlaced fashion. 1080p refers to the progressive nature of the storage.


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1080i/p Confusion

There is a great deal of confusion regarding the differences between 1080i and 1080p.

Film Content

For film content, for example those found on Blu-ray or HD DVD, they are stored as 1080p/24, which means a 1080-line progressive video with 24 frames per second. Some HD DVD players only have 1080i output, and some displays only have 1080i inputs (even when they support 1080p mode) - this has led some to believe that players/displays with 1080p output/input will produce a superior picture. This is not entirely true, in fact, in most cases, this is not true at all. It is easier to explain with an example:

Example 1: A HD DVD player has 1080p output 24 fps. The HD DVD movie being played is stored in 1080p/24 fashion. The display connected to the HD DVD player has a native resolution of 1080 lines, and it supports both 1080i and 1080p input. 1080p output mode is used on the HD DVD player With this connection, the displays receives the transmission as a series of 1080 line progressive frames, and then displays it accordingly.

Example 2: The same player, movie and display as above, except now that the player's output mode is changed to 1080i/60 (60 fields per second). The display receives the transmission as odd and even fields of 540 lines each, 48 fields altogether for the 24 fps film (2 fields for each frame). The display recognises that the content being played is film content, and then combines the odd and even fields into a series of 1080 line progressive frames, and then displays it accordingly.

As you can see from the above examples, the picture you are seeing on screen is identical in both cases, there is no difference in quality at all unless the display fails to recognise the content being played as film content, or if the display's de-interlacer is of cheap quality (a cheap de-interlacer is unable to combine fields, rather, it line doubles each field to make a frame so you are only seeing 540 lines of detail in each frame. Note that since 1080-line displays are considered very high end, and it is unlikely they are fitted with cheaper de-interlacers). Also, unlike old CRT TV, most modern displays (LCD, plasma) are progressive in nature, so all interlaced content are converted in this fashion to a progressive image, and not displayed in an interlaced fashion at all.

Gaming

While for film content, 1080i and 1080p in most cases will offer no difference, it is somewhat different for gaming.

For example, the PS3 supports 1080p output, while the Xbox 360 mainly supports 1080i output (although 1080p is available using the VGA cable accessory, or through the HDMI output on the Elite version of the console). Some PS3 games support 1080p output at 30 FPS, and this is identical to an Xbox 360 games at 1080i/60 (60 fields => 30 frames), especially when viewed on a progressive/digital display.

But some PS3 games support 1080p output at 60 FPS, and in this case, the Xbox 360 game at 1080i/60 will only offer half of the framerate as the PS3 game, although both are displaying 1080 lines of information. Note that this is only an example, and Xbox 360 games with 1080p/60fps are said to be available in the future. And it's also worth noting that some games, when used at 1080p/60fps mode, will reduce details/quality in order ensure no frame drops.

See Also