The aspect ratio of an image is its width divided by its height.
Aspect ratios are mathematically expressed as x :y (pronounced "x-to-y") and x×y (pronounced "x-by-y"). 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), universal for standard-definition video formats, and 16:9 (1.78:1), universal to 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 and 3:2, though other aspect ratios, such as 5:4, 7:5, and 1:1 (square format), are used.
Converting formats of unequal ratios is done by either cropping the original image to the receiving format's aspect ratio, by adding horizontal mattes (letterboxing) or vertical mattes (pillarboxing) to retain the original format's aspect ratio, or by distorting the image to fill the receiving format's ratio. Cinematographic aspect ratios are usually denoted as a decimal fraction width to unit height, while videographic aspect ratios are usually denoted by ratios of whole numbers.
When the 16:9 aspect ratio was proposed by Kerns H. Powers, nobody was creating 16:9 video. The popular choices in 1980 were 4:3, 15:9, 1.85, 2.20 and 2.35. Powers discovered that all of those aspects would fit within a 1.78:1 outer rectangle and when over-lapped, all shared a common 16:9 inner rectangle. Hence, any of the "common 5" can be neatly cropped or matted to fill a 16:9 screen.
While 1.78:1 was initially selected as a compromise format, the popularity of HDTV broadcast has solidified 1.78:1 as perhaps the most important video aspect ratio going forward. Most 1.33:1 and 2.35:1 video is now recorded such that a 1.78:1 inner rectangle is "protected" for HD broadcast. Meanwhile, the 1.33:1 (4:3) aspect is declining in popularity.
In motion picture formats, the physical size of the film area between the sprocket perforations determines the image's size. The universal standard (established by William Dickson and Thomas Edison in 1892) is a frame that is four perforations high. The film itself is 35 mm wide (1.38 in), but the area between the perforations is 24.89 mm×18.67 mm (0.980 in×0.735 in). With a space designated for the standard optical soundtrack, and the frame size reduced to maintain an image that is wider than taller (mimicking human eyesight), this resulted in the Academy aperture of 22 mm×16 mm (0.866 in×0.630 in) or 1.37:1 aspect ratio.
The motion picture industry convention assigns a value of 1.0 to the image’s height, thus, an anamorphic frame is described as 2.40:1 or 2.40 ("two-four-oh"). In American cinemas, the common projection ratios are 1.85:1 and 2.40:1. Some European countries have 1.66:1 as the wide screen standard. 1.33:1 was used for all cinema films until the 1950s. However, when television, which also had a screen ratio of 1.33:1, became a threat to movie audiences, Hollywood gave birth to a large number of wide-screen formats: Cinemascope, Todd-AO, and VistaVision (to name just a few). During the 1950s the 1.85:1 aspect ratio became one of the most common cinema projection standards in the U.S..
Development of various camera systems must therefore ultimately cater to the placement of the frame in relation to these lateral constraints of the perforations and the optical soundtrack area. One clever wide screen alternative, VistaVision, used standard 35 mm film running sideways through the camera gate, so that the sprocket holes were above and below frame, resulting in a larger horizontal negative size per frame as the vertical size was now restricted by the perforations. 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 (on standard 4-perforation 35 mm film) to show in the projectors available at theaters. Though the format was briefly revived by Lucasfilm in the 1970s for special effects work that required larger negative size (due to image degradation from the optical printing steps necessary to make multi-layer composites), it went into obsolescence largely due to better cameras, lenses, and film stocks available to standard 4-perforation formats, in addition to increased lab costs of making prints in comparison to more standard vertical processes. (The horizontal process was later adapted to 70 mm film by IMAX.)
Super 16 mm film is frequently used for television production due to its lower cost, lack of need for soundtrack space on the film itself (as it is not projected but rather transferred to video), and aspect ratio similar to 16:9 (Super 16 mm is natively 1.66 whilst 16:9 is 1.78). It also can be blown up to 35 mm for theatrical release and therefore is also used for feature films.
|United Kingdom||Almost all main channels|
|Belgium|| Flanders: all main channels|
Wallonia: La Une, La Deux, RTL TVI, Club RTL, Plug TV
|France||France 2, France 5, Arte, NRJ 12, Luxe TV|
|Germany||ARD, ZDF, EinsExtra, EinsFestival, EinsPlus, Arte, Phoenix, Deutsche Welle, Das Erste, Bayerisches Fernsehen, Hessen Fernsehen, WDR Fernsehen Köln, BR-alpha, Südwest Fernsehen Baden-Würtemberg, 3sat, RBB Brandenburg, RBB Berlin, Radio Bremen TV, RTL Television, ProSieben|
|Austria||ORF1, ORF2, ORF Sport Plus and ORF1 HD|
|Switzerland||All SRG SSR idée suisse channels|
|Italy||SKY Italia, Rai Sport Più|
|Denmark||Almost all main channels|
|Sweden||Almost all main channels|
|Norway||Almost all main channels|
|Poland||Polsat 2, Polsat News, Polsat Sport, Polsat Sport Extra, Ale Kino!, Religia TV|
|Bosnia and Herzegovina||RTV BN, TV Mostar, Radio Televizija Republike Srpske|
|Finland||YLE TV1, YLE TV2, MTV3, Nelonen|
|Slovakia||TV Markiza, Slovenská Televízia|
|Netherlands||Public Channels, RTL, SBS|
|Czech||TV Nova, Česká televize, TV Nova HD|
Comparing two different aspect ratios is arguably difficult. Given the same diagonal, the 4:3 screen offers more area. For CRT-based technology, an aspect ratio that is closer to square is cheaper to manufacture. The same is true for projectors, and other optical devices such as cameras, camcorders, etc. For LCD and Plasma displays, however, the cost is proportional to the area. Therefore, 16:9 screens are cheaper than 4:3 screens with the same diagonal.
Two aspect ratios compared with images using the same diagonal size:
|4:3||35 mm original silent film ratio, commonly known in TV and video as 4:3. Also standard ratio for MPEG-2 video compression.|
|1.37||35 mm full-screen sound film image, nearly universal in movies between 1932 and 1953. Officially adopted as the Academy ratio in 1932 by AMPAS. Still occasionally used. Also standard 16 mm.|
|1.43||IMAX format. Imax productions use 70 mm wide film (the same as used for 70 mm feature films), but the film runs through the camera and projector sideways. This allows for a physically larger area for each image.|
|1.5:1||The aspect ratio of 35 mm film used for still photography.|
|1.56:1||Widescreen aspect ratio 14:9. Often used in shooting commercials etc. as a compromise format between 4:3 (12:9) and 16:9, especially when the output will be used in both standard TV and widescreen. When converted to a 16:9 frame, there is slight pillarboxing, while conversion to 4:3 creates slight letterboxing.|
|15:9||35 mm European widescreen standard; native Super 16 mm frame ratio. (5:3, sometimes expressed more accurately as "1.67".)|
|1.75||Early 35 mm widescreen ratio, primarily used by MGM and Warner Bros., and since abandoned.|
|16:9||Video widescreen standard (16:9), used in high-definition television, one of three ratios specified for MPEG-2 video compression.|
|1.85||35 mm US and UK widescreen standard for theatrical film. Uses approximately 3 perforations ("perfs") of image space per 4 perf frame; films can be shot in 3-perf to save cost of film stock.|
|2.00||Original SuperScope ratio, also used in Univisium. Flat ratio in the 1950s, abandoned in the 1960s.|
|2.20||70 mm standard. Originally developed for Todd-AO in the 1950s. 2.21:1 is specified for MPEG-2 but not used.|
|2.35||35 mm anamorphic prior to 1970, used by CinemaScope ("'Scope") and early Panavision. The anamorphic standard has subtly changed so that modern anamorphic productions are actually 2.39, but often referred to as 2.35 anyway, due to old convention. (Note that anamorphic refers to the compression of the image on film to maximize an area slightly taller than standard 4-perf Academy aperture, but presents the widest of aspect ratios.)|
|2.39||35 mm anamorphic from 1970 onwards. Sometimes rounded up to 2.40:1 Often commercially branded as Panavision format or 'Scope.|
|2.55||Original aspect ratio of CinemaScope before optical sound was added to the film. This was also the aspect ratio of CinemaScope 55.|
|2.59||Cinerama at full height (three specially captured 35 mm images projected side-by-side into one composite widescreen image).|
|2.66||Full frame output from Super 16mm negative when an anamorphic lens system has been used. Effectively, an image that is of the ratio 2.66.1 is squashed onto the native 15:9 aspect ratio of a Super 16mm negative.|
|2.76||MGM Camera 65 (65 mm with 1.25x anamorphic squeeze). Used only on a handful of films between 1956 and 1964, such as Ben-Hur (1959).|
|4.00||Polyvision, three 35 mm 1.33 images projected side by side. Used only on Abel Gance's Napoléon (1927).|
Original Aspect Ratio (OAR) is a home cinema term for the aspect ratio or dimensions in which a film or visual production was produced — as envisioned by the people involved in the creation of the work. As an example, the film Gladiator was released to theaters in the 2.39:1 aspect ratio. It was filmed in Super 35 mm film and, in addition to being presented in cinemas and television in the Original Aspect Ratio of 2.39:1, it was also broadcast without the matte altering the aspect ratio to the television standard of 1.33:1. Because of the varied ways in which films are shot, IAR (Intended Aspect Ratio) is a more appropriate term, but is rarely used.
Modified Aspect Ratio is a home cinema term for the aspect ratio or dimensions in which a film was modified to fit a specific type of screen, as opposed to original aspect ratio. Modified aspect ratios are usually either 1.33:1 (historically), or (with the advent of widescreen television sets) 1.78:1 aspect ratio. 1.33:1 is the modified aspect ratio used historically in VHS format. A modified aspect ratio transfer is achieved by means of pan and scan or open matte, the latter meaning removing the cinematic matte from a 1.85:1 film to open up the full 1.33:1 frame.
Multiple aspect ratios create additional burdens on filmmakers and consumers, and confusion among TV broadcasters. It is common for a widescreen film to be presented in an altered format (cropped, letterboxed or expanded beyond the Original Aspect Ratio). It is also not uncommon for windowboxing to occur (when letterbox and pillarbox happen simultaneously). For instance, a 16:9 broadcast could embed a 4:3 commercial within the 16:9 image area. A viewer watching on a standard 4:3 (non-widescreen) television would see a 4:3 image of the commercial with 2 sets of black stripes, vertical and horizontal (windowboxing or the postage stamp effect). A similar scenario may also occur for a widescreen set owner when viewing 16:9 material embedded in a 4:3 frame, and then watching that in 16:9. It is also not uncommon that a 4:3 image is stretched horizontally to fit a 16:9 screen to avoid pillar boxing.
Both PAL and NTSC have provision for some data pulses contained within the video signal used to signal the aspect ratio (See ITU-R BT.1119-1 - Widescreen signaling for broadcasting). These pulses are detected by television sets that have widescreen displays and cause the television to automatically switch to 16:9 display mode. When 4:3 material is included (such as the aforementioned commercial), the television switches to a 4:3 display mode to correctly display the material. Where a video signal is transmitted via a European SCART connection, one of the status lines is used to signal 16:9 material as well.
For many artists, however, aspect ratio is determined not by the constraints of the technology or medium, but by the content or the story. Indeed, as long ago as the early 20th century, film directors such as D. W. Griffith, one of the early giants in film, would sometimes change the picture aspect ratio within the film. In "Intolerance", for example, a single shot where a character falls from a high wall has the sides of the vista greatly cropped to enhance the dramatic height of the fall. More recently, the initial Itchy and Scratchy sketch in The Simpsons Movie is shown in 16:9 ratio, and during the opening the screen widens to 2.35:1.
Today, directors of photography are often forced to compose the shot to keep the essential subjects in the "sweet spot" of the frame, as a compositional compromise between the intended aspect ratio and the potential future alternate ratios to be presented.
Common aspect ratios in still photography include 4:3 (1.33) used by most point-and-shoot digital cameras; 3:2 (1.5) used by 35mm film, APS-C ("classic" mode) and most DSLRs; 1.81:1 (close to 16:9) used by APS-H high definition mode; 3:1 used by APS-P panoramic mode; and 1:1 (square) in a variety of cameras.
Common print sizes in the U.S. (in inches) include 4x6 (1.5), 5x7 (1.4), 4x5 and 8x10 (1.25), and 11x14 (1.27); large-format cameras typical use one of these aspect ratios. Medium-format cameras typically have format designated by nominal sizes in centimeters (6x6, 6x7, 6x9, 6x4.5), but these numbers should not be interpreted as exact in computing aspect ratios.