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Aspect ratio (image)

From Academic Kids

For an article on the aeronautical term, see aspect ratio (wing). For other uses of aspect ratio, please see its disambiguation page.

The aspect ratio of an image is its displayed width divided by its height (usually expressed as "x:y"). For instance, the aspect ratio of a traditional television screen is 4:3, or 1.33:1. High definition television uses an aspect of 16:9, or about 1.78:1. Aspect ratios of 2.39:1 or 1.85:1 are frequently used in cinematography, while the aspect ratio of a full 35mm film frame with soundtrack (also known as "Academy standard") is around 1.37:1.

Missing image
Aspect_ratios.png
Comparison of three common aspect ratios. The outer box (blue) and middle box (red) are common formats for cinematography. The inner box (green) is the format used in standard television.

The 4:3 ratio for standard television has been in use since television's origins and many computer monitors use the same aspect ratio. Since 4:3 is close to the old 1.37:1 cinema academy format, theaters suffered from a loss of viewers after films were broadcast on TV. To prevent this, Hollywood created widescreen aspect ratios to immerse the viewer in a more realistic experience and, possibly, to make broadcast films less enjoyable if watched on a regular TV set.

16:9 is the format of Japanese and American HDTV as well as European non-HD widescreen television (EDTV). Many digital video cameras have the capability to record in 16:9. Anamorphic DVD transfers store the information in 16:9 vertically squeezed to 4:3; if the TV can handle an anamorphic image the signal will be de-anamorphosed by the TV to 16:9, if not the DVD player will unsqueeze the image and add letterboxing before sending the image to the TV. Wider ratios such as 1.85:1 and 2.39:1 are accommodated within the 16:9 DVD frame by adding some additional masking within the image itself.

Within the motion picture industry, the convention is to assign a value of 1 to the image height, so that, for example, an anamorphic frame is described as 2.39:1 or just "2.39". This way of speaking comes about because the width of a film image is restricted by the presence of sprocket holes and a standard intermittent movement interval of 4 perforations, as well as an optical soundtrack running down the projection print between the image and the perforations on one side. The most common projection ratios in American theaters are 1.85 and 2.39.

Development of various camera systems must therefore ultimately cater to the placement of the frame in relation to these lateral constraints. For example, one clever widescreen process, VistaVision, used standard 35mm film running sideways through camera gate, so that the sprocket holes were above and below frame, resulting in a larger negative size per frame. However, the 1.5 ratio of the initial VistaVision image needed to be cropped down to 1.85 and optically converted to a vertical print for projection. Though the format was briefly revived by Lucasfilm in the 1970's for special effects work that required larger negative size due to image degradation, it went into obsolescence largely due to better cameras, lenses, and film stocks, in addition to increased lab costs of making prints in comparision to more standard vertical processes.

The 16:9 format adopted for HDTV is actually narrower than commonly-used cinematic widescreen formats. Anamorphic widescreen (2.39:1) and American theatrical standard (1.85:1) have wider aspect ratios, while the European theatrical standard (1.66:1) is just slightly less. (IMAX, contrary to some popular perception, is 1.33:1, the traditional television aspect ratio.)

Super 16mm film is frequently used for television production due to its lower cost, lack of need for soundtrack space on the film itself, and aspect ratio similar to 16:9 (Super 16mm is natively 1.66 whilst 16:9 is 1.78).

Aspect ratios compared
4:3 (1.33:1)16:9 (1.78:1)
Image:4_3_example.jpgMissing image
16_9_example.jpg
Image:16_9_example.jpg

The term is also used in the context of computer graphics to describe the shape of an individual pixel in a digitized image. Most digital imaging systems use square pixels—that is, they sample an image at the same resolution horizontally and vertically. But there are some devices that do not, so a digital image scanned at twice the horizontal resolution to its vertical resolution might be described as being sampled at a 2:1 aspect ratio, regardless of the size or shape of the image as a whole.

Missing image
Aspect_ratio.compare6.png
Comparison of common aspect ratios

Historic and commonly used aspect ratios

  • 1.33 - 35 mm original silent film ratio, common in TV and video as 4:3. Also standard ratio for IMAX.
  • 1.37 - 35 mm full-screen sound film image, nearly universal in movies between 1928 and 1953. Still occasionally used. Also standard 16 mm.
  • 1.66 - 35 mm European widescreen standard, also Super 16 mm.
  • 1.75 - early 35 mm widescreen ratio, since abandoned.
  • 1.78 - video widescreen standard (16:9)
  • 1.85 - 35 mm US and UK widescreen standard. Uses approximately 3 perfs of image space per 4 perf frame; films can be shot in 3-perf to save cost of film stock.
  • 2.20 - 70 mm standard
  • 2.35 - 35 mm anamorphic prior to 1970. Cinemascope ('Scope) and early Panavision. The standard has subtly changed so that modern productions are actually 2.39, but often referred to as 2.35 anyway, due to old convention. No recent films are 2.35.
  • 2.39 - 35 mm anamorphic from 1970 onwards. Sometimes rounded up as 2.4
  • 2.59 - Cinerama at full height (three specially captured 35 mm images projected side-by-side into one composite widescreen image)
  • 2.75 - 70 mm anamorphic (Ultra Panavision). Only used on a handful of films between 1956 and 1964.
  • 4.00 - Polyvision, three 35 mm 1.33 images projected side by side. Only used on Abel Gance's Napoleon (1927)

See also

External links

de:16:9 sv:16:9 de:Aspect ratio ja:画面サイズ

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