- published: 11 Dec 2013
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The aspect ratio of an image describes the proportional relationship between its width and its height.
It is commonly expressed as two numbers separated by a colon, as in 16:9. For an x:y aspect ratio, no matter how big or small the image is, if the width is divided into x units of equal length and the height is measured using this same length unit, the height will be measured to be y units. For example, consider a group of images, all with an aspect ratio of 16:9. One image is 16 inches wide and 9 inches high. Another image is 16 centimeters wide and 9 centimeters high. A third is 8 yards wide and 4.5 yards high.
The most common aspect ratios used today in the presentation of films in movie theaters are 1.85:1 and 2.39:1. Two common videographic aspect ratios are 4:3 (1.33:1), the universal video format of the 20th century and 16:9 (1.77:1), universal for high-definition television and European digital television. Other cinema and video aspect ratios exist, but are used infrequently.
In still camera photography, the most common aspect ratios are 4:3, 3:2, and more recently being found in consumer cameras 16:9. Other aspect ratios, such as 5:3, 5:4, and 1:1 (square format), are used in photography as well, particularly in medium format and large format.
The aspect ratio is the ratio of the width of a shape to its height when the width is larger than the height, i.e. the shape is positioned as a "landscape" rather than "portrait".
It may be applied to two characteristic dimensions of a three-dimensional shape.
The term is most commonly used with reference to:
For a rectangle, the aspect ratio denotes the ratio of length to width of the rectangle. An aspect ratio of 1:1 is a square.
From left to right:
For an ellipse, the aspect ratio denotes the ratio of the major axis to the minor axis. An aspect ratio of 1:1 is a circle.
Aspect ratios are mathematically expressed as x:y (pronounced "x-to-y") and x×y (pronounced "x-by-y"), with the latter particularly used for pixel dimensions, such as 640×480. Cinematographic aspect ratios are usually denoted as a (rounded) decimal multiple of width vs unit height, while photographic and videographic aspect ratios are usually defined and denoted by whole number ratios of width to height. In digital images there is a subtle distinction between the Display Aspect Ratio (the image as displayed) and the Storage Aspect Ratio (the ratio of pixel dimensions); see distinctions, below.