The evolution of film and TV aspect ratios
Original aspect ratio
Letterboxing and Pillar Boxing
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 sync-sound 35 mm film frame is around 1.37:1 (also known as "Academy" ratio). Silent films which used the full frame were shot in 1.33:1.
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 the aspect ratio of the usable frame within the Academy format once the soundtrack had been taken into account, films could be satisfactorily viewed on TV in the early days of the medium. When cinema attendance dropped, 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 stretched 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 unstretch 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.
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).
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Original Aspect Ratio 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 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 mattes its original aspect ratio release had.
Letterboxing and pillar boxing
Letterboxing is the practice of transferring widescreen films to video formats while preserving the original aspect ratio. Since the video display is most often a more square aspect ratio than the original film, the resulting video must include masked-off areas above and below the picture area (often referred to as "black bars," or, more accurately, as mattes). Letterboxing takes its name from the similarity of the resulting image to a horizontal opening in a postal letter box.
Letterboxing offers an alternative to the pan and scan or full screen method of transferring a widescreen film to video. In pan and scan, the original image is cropped to to suit the 1.33:1 (or 4:3) ratio of the television screen. In contrast, letterboxing preserves most of the original composition of the film as seen in the theater.
Pillar boxing refers to what happens when a 1.33:1 image is displayed on a wider screen, adding bars on the side. The pillar box effect occurs in widescreen video displays when black bars (mattes or masking) are placed on the sides of the image. It becomes necessary when video that was not originally designed for widescreen is shown on a widescreen display. The original material is shrunk and placed in the middle of the widescreen frame. "Pillar box", sometimes called windowboxing, comes from the similarity of this display to free-standing mailboxes in the UK and the British Commonwealth.
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