Everything about Pixel Aspect Ratio totally explained
The term
pixel aspect ratio is used in the context of
computer graphics to describe the layout of
pixels in a digitized image. Most digital
imaging systems use a square grid of pixels—that is, they sample an image at the same resolution horizontally and vertically. But there are some devices that don't (most notably some common
standard-definition formats in
digital television and
DVD-Video) so a digital image scanned at a vertical resolution twice that of its horizontal resolution (for example the pixels are twice as close together vertically as horizontally) might be described as being sampled at a 2:1 pixel aspect ratio, regardless of the size or shape of the image as a whole.
Increasing the aspect ratio of an image makes its use of pixels less efficient, and the resulting image will have lower perceived detail than an image with an equal number of pixels, but arranged with an equal horizontal and vertical resolution. Beyond about 2:1 pixel aspect ratio, further increases in the already-sharper direction will have no visible effect, no matter how many more pixels are added. Hence an NTSC picture (480i) with 1000 lines of horizontal resolution is possible, but would look no sharper than a DVD. The exception to this is in situations where pixels are used for a purpose other than resolution - for example, a printer that uses dithering to simulate gray shades from black-or-white pixels, or analog videotape that loses high frequencies when dubbed.
Different pixel aspect ratios
| Video Standard |
Pixel aspect ratio |
| PAL CCIR-601/ITU-R 601 (720x576) |
1.0666:1The correct figure for this is 1.094:1 TV pixels are not square
see http://www.bbc.co.uk/commissioning/tvbranding/picturesize.shtml for an explantion
|
| PAL Square Pixel (768x576) |
1:1the correct aspect here's 788x576. TV pixels are not square
see http://www.bbc.co.uk/commissioning/tvbranding/picturesize.shtml for an explantion
|
| D1/DV NTSC |
0.9117:1 |
| D1/DV NTSC 16:9 |
1.2121:1 |
| D1/DV PAL |
1.064:1The correct figure for this is 1.094:1 TV pixels are not square
see http://www.bbc.co.uk/commissioning/tvbranding/picturesize.shtml for an explantion
|
| D1/DV PAL 16:9 |
1.4587:1 |
| HD 720 (1280x720) |
1:1 |
| HDV (1440x1080) |
1.333:1 |
| HD 1080 (1920x1080) |
1:1 |
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