Aspect Ratio

relation between the width and height of an image on the screen

The aspect ratio of a two-dimensional shape is the ratio of its longer dimension to its shorter dimension. It is also applied to two characteristic dimensions of a three-dimensional shape, especially for the longest and shortest 'axes' or for symmetrical objects (e.g. rods) that are described by just two measures (e.g. length and diameter). In such cases, the aspect ratio may evaluate to a value less than one (e.g. consider very short and very long rods).
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The aspect ratio of an image is its displayed width divided by its height (usually expressed as "x:y" or "x×y," with the joining colon or multiplication symbol articulated as the preposition "by" or sometimes "to"). Currently, the most common motion picture film ratios in use are 1.85:1 and 2.39:1. In video, the two standardized ratios are currently the traditional 4:3 (1.33:1), universal among standard definition video formats, and its modern 16:9 (1.78:1) successor, used in high-definition television and European digital television. Historically, many other aspect ratios no longer in general use have existed in both film and video. Conversion between formats with unequal ratios can be accomplished by either cropping the image to fit the receiving format's ratio or adding black bars (letterboxing or pillarboxing) to retain the original format's ratio. Film ratios tend to be formatted to end with ":1", while video ratios usually prefer to be denoted with whole numbers on both sides of the ratio.
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Noun
1. the ratio of the width to the height of a tv picture
(hypernym) ratio

In facsimile or television, the ratio of the width to the height of a picture, document, or scanning field.

<graphics> The ratio of width to height of a pixel, image, or display screen. Square pixels (1:1) are considered preferable but displays are usually about 5:4.
(1994-11-30)