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.
[The 2.39:1 ratio is commonly labeled 2.40:1, e.g., in the American Society of Cinematographers' American Cinematographer Manual, and is mistakenly referred to as 2.35:1 (only cinema films before the 1970 SMPTE revision used 2.35:1).] 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,
3:2, and more recently being found in consumer cameras, previously only commonly seen in professional cameras,
16:9. Other aspect ratios, such as
5:4,
6:7, and
1:1 (square format), are used in photography as well.
In television and on DVDs, converting formats of unequal ratios is done by cropping the original image to the receiving format's aspect ratio (
zooming), 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.
Practical limitations
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), leaving the de facto ratio of 4:3, or 1.33:1.
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.
Cinema terminology
The
motion picture industry convention assigns a value of 1.0 to the image’s height; thus, an
anamorphic frame (actually 2.39:1) is described (rounded) 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. The "Academy ratio" of 1.37:1 was used for all cinema films until 1953 (with the incarnation of
George Stevens's
Shane). During that time, television, which had a similar aspect 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. The "flat" 1.85:1 aspect ratio was introduced in May, 1953, and became one of the most common cinema projection standards in the U.S. and elsewhere.
Movie camera systems
Development of various film camera systems must ultimately cater to the placement of the frame in relation to the 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, allowing a larger horizontal negative size per frame as only the vertical size was now restricted by the perforations. However, the 1.50:1 ratio of the initial VistaVision image was optically converted to a vertical print (on standard 4-perforation
35 mm film) to show in the projectors available at theaters, and was then masked in the projector to the US standard of 1.85:1. 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 (the native ratio of Super 16 mm 1.66:1 while 16:9 is 1.78:1). It also can be blown up to 35 mm for theatrical release and therefore is also used for feature films.
Current video standards
4:3 standard
The 4:3 ratio (generally named as
"Four-Three",
"Four-by-Three",
"Four-to-Three", or
"Academy Ratio") for standard television has been in use since television's origins and many
computer monitors use the same aspect ratio. 4:3 is the aspect ratio defined by the
Academy of Motion Picture Arts and Sciences as a standard after the advent of optical
sound-on-film. By having TV match this aspect ratio, films previously photographed on film could be satisfactorily viewed on TV in the early days of the medium (i.e. the 1940s and the 1950s). When
cinema attendance dropped, Hollywood created
widescreen aspect ratios (such as the 1.85:1 ratio mentioned earlier) in order to differentiate the film industry from TV.
16:9 standard
16:9 (generally pronounced as
"Sixteen-by-Nine"; alternates include
"Sixteen-Nine" and
"Sixteen-to-Nine") is the international standard format of
HDTV as used in
Australia,
Brazil,
Canada,
Japan,
South Korea, and the
United States, as well as in
Europe on
HDTV, non-HD digital
television and analog widescreen television (
EDTV)
PALplus. Japan's
Hi-Vision originally started with a 5:3 ratio but converted when the international standards group introduced a wider ratio of 5⅓ to 3 (=16:9). Many
digital video cameras have the capability to record in 16:9.
Anamorphic transfers onto
DVD horizontally squeeze the original widescreen image to store the information into a 4:3 aspect ratio DVD frame. If the TV has a feature to un-squeeze an anamorphic image, it will horizontally decompress the image to 16:9. If not, many DVD players can also reduce scan lines and add
letterboxing bars above and below the image before sending it to the TV. Made easier by the simple 4:3 aspect ratio between 4:3 and 16:9 (16:9 = 4:3 × 4:3). DVD producers can also choose to show even wider ratios such as 1.85:1 and 2.39:1
within the 16:9 DVD frame by
hard matting or adding black bars within the image itself. Some films which were made in a 1.85:1 aspect ratio, such as the U.S.-Italian co-production
Man of La Mancha, fit quite comfortably onto a 1.78:1 HDTV screen and have been issued anamorphically enhanced on DVD without the black bars.
Why 16:9 was chosen by the SMPTE
thumb|right|300px|Equal area comparison of the aspect ratios used by Dr. Powers to derive the SMPTE 16:9 standard./2.2 in mauve and
CinemaScope/2.35 in purple.]]When the 16:9 aspect ratio was proposed by Dr.
Kerns H. Powers, a member of the
SMPTE Working Group On High-Definition Electronic Production, nobody was creating 16:9 videos. The popular choices in 1980 were: 4:3 (based on television standard's ratio at the time), 1.66:1 (the European "flat" ratio), 1.85:1 (the American "flat" ratio), 2.20:1 (the ratio of 70 mm films and
Panavision) and 2.35:1 (the
CinemaScope ratio for
anamorphic widescreen films). Dr. Powers cut out rectangles with equal areas and shaped them to match each of the popular aspect ratios. When overlapped with their center points aligned, he found that all of those aspect ratio rectangles fit within an outer rectangle with an aspect ratio of 1.78:1 and all of them also covered a smaller common inner rectangle with the same aspect ratio 1.78:1.
The
geometric mean of the extreme aspect ratios, 4:3 (1.33:1) and 2.35:1, is also 1.77:1 which is coincidentally close to 16:9 (1.78:1).
While 16:9 (1.78:1) was initially selected as a compromise format, the subsequent popularity of HDTV broadcast has solidified 16:9 as perhaps the most important video aspect ratio for the future. Most 4:3 (1.33:1) and 2.39:1 video is now recorded using a "shoot and protect" technique that keeps the main action within a 16:9 (1.78:1) inner rectangle to facilitate HD broadcast.
After the original
16:9 Action Plan of the early 1990s, the
European Union has instituted the 16:9 Action Plan, just to accelerate the development of the advanced television services in 16:9 aspect ratio, both in
PAL and also in
HDTV. The Community fund for the 16:9 Action Plan amounted to
€228 million.
16:9 in Europe
In Europe, 16:9 is being adopted as the standard broadcast format for digital and high definition TV. Some countries have even adopted the format for analog television by means of the
PALplus standard.
Obtaining height, width and area of the screen
Often, screen specifications are given by their diagonal length. Here are some formulae that can help in the finding of height, width and area, where r stands for ratio and d for diagonal length.
Visual comparisons
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 more related to the area, so producing wider and shorter screens with the same advertised diagonal is more profitable. Making tolerable vertical viewing angle for LCD has always been challenging, which explains why LCD manufacturers were so eager to embrace shortscreen lately.
- Two aspect ratios compared with images using the same diagonal size:
- Two aspect ratios compared with images using the same area (number of pixels):
- Two aspect ratios compared with images using the same height (vertical size):
- Two aspect ratios compared with images using the same width (horizontal size):
Previous and presently used aspect ratios
Aspect ratio releases
Original aspect ratio (OAR)
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 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 (MAR)
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.
Problems in film and television
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.
Active Format Description is a mechanism used in digital broadcasting to avoid this problem. It is also common 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.
Still photography
Common aspect ratios in still photography include 4:3 (1.33) used by most
point-and-shoot cameras and
Four Thirds system 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 and some Panasonic multi‐aspect Four Thirds and compact cameras; 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 4×6 (1.5), 5×7 (1.4), 4×5 and 8×10 (1.25), and 11×14 (1.27);
large format cameras typically use one of these aspect ratios.
Medium-format cameras typically have format designated by nominal sizes in centimeters (6×6, 6×7, 6×9, 6×4.5), but these numbers should not be interpreted as exact in computing aspect ratios.
See also
