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The term pixel aspect ratio, sometimes shortened to aspect ratio, is also used in the context of computer graphics to describe the distribution of pixel 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 do not (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 (i.e. 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.

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