- For an article on the aeronautical term, see aspect ratio (wing).
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 2.35:1 or 1.85:1 are frequently used in cinematography, while the aspect ratio of a standard 35mm film frame is around 1.37:1.
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 2.35:1 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, a Cinemascope frame is described as 2.35:1 or just "2.35". This way of speaking comes about because the width of a film image is restricted by the presence of sprocket holes and, usually, an optical soundtrack on the projection print . Development of various camera systems therefore centers on the placement of the frame in relation to these lateral constraints; the height of image can be adjusted freely, so the ingenuity goes into getting different widths. One clever widescreen process, VistaVision, used standard 35mm film running sideways through camera gate, so that the sprocket holes were above and below frame and the width was not restricted. The most common projection ratios in American theaters are 1.85 and 2.35.
The 16:9 format adopted for HDTV is actually narrower than commonly-used cinematic widescreen formats. Anamorphic widescreen (2.35:1) 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.)
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.
Aspect ratios compared
| 4:3 (1.33:1) |
16:9 (1.78:1) |
|
|
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.
See also
External links
Last updated: 05-13-2005 00:27:41
