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Aspect ratio demystified

Whenever we talk about the ‘aspect ratio’ of a film or a video, we’re simply talking about the shape of the image. It refers to the ratio between the width of a rectangular frame and its height, and is normally written in the form width:height (1:1 is, of course, a perfect square).

A common ratio is 16:9, which is the standard profile of modern TV screens; they are available at various different sizes, but they all have the same proportions. Occasionally, you might see an aspect ratio described as a single number – in this case, the number refers to the width where the height is 1. For example, 4:3 can be written as 1.33:1 or simply, 1.33.

Terms like widescreen, CinemaScope and Academy Ratio describe specific formats, but aspect ratio also comes into play when we use terms like Standard Definition or HDTV, because they incorporate a screen shape as well as resolution.

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Into the frame

In 1889 Thomas Edison’s assistant, William Kennedy Dickson, devised the first movie film by splitting a reel of 70mm medium format photographic film in two, and pasting it onto a celluloid strip 35mm wide.

Aspect ratio
Image from Blacksmith Scene, the first known film to use Dickson’s 4:3 ratio

Influenced both by the dimensions of the commonly available still photography film, and his own idea of the aesthetics of shot composition, Dickson specified an aspect ratio of approximately 4:3. By 1917, the newly formed Society of Motion Picture Engineers adopted Dickson’s 35mm film, which subsequently became the predominant format used throughout the 20th Century.

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There were two big advances in cinema technology during the first half of the 20th Century that influenced the aspect ratio of the projected images in cinemas. The first was the introduction of sound.

Soundtracks were either recorded separately onto discs, which were then synchronised with the projection in the cinema, or the soundtrack was recorded optically on the film so that synchronisation was automatic.

As optical soundtracks grew in popularity, the size of the film frame was altered to make room for the audio. The aspect ratio was changed from 1:33:1 to 1.15:1, making the image area slightly narrower and therefore leaving room for the optical soundtrack.

Rectangular peg in a square hole

This gave cinemas a bit of a headache because their projection screens were all designed for the wider 1.33:1 image. Consequently, cinemas started to use metal plates with a hole cut to correspond to the original 1:33 aspect ratio, masking off the top and bottom of the image. When the projector lens was adjusted, the cinemas could fill their screens again.

The studios,however, didn’t like movie theatres cropping their films, and eventually the situation was resolved by the introduction of the ‘Academy Ratio’.

The Academy of Motion Picture Arts and Sciences introduced the film format in 1932, which defined new frame dimensions without affecting the area storing the soundtrack. By slightly increasing the height of the black gap between frames, they changed the aspect ratio to 1.37:1, which was so close to Dickson’s original 1.33:1 ratio that cinemas didn’t need to modify their projection systems.

Although the Academy Ratio’s frame size was physically smaller than before, improvements in film technology meant that there was no noticeable loss of quality.

Academy Ratio is rarely used in modern filmmaking, but there are notable exceptions. The Grand Budapest Hotel, directed by Wes Anderson, uses three different aspect ratios to represent three different periods of time: 1.85:1, 2.35:1 and Academy Ratio.

aspect ratio
Academy ratio still frame from The Grand Budapest Hotel (2014) directed by Wes Anderson

The threat from TV

The second technological change to affect film was the introduction of various widescreen formats from the middle of the 1950s.

Television broadcast standards originally set the aspect ratio of TV screens to 1.33:1, which made sense, given the wealth of Hollywood content that already existed in that ratio, plus the fact that film cameras were often used to shoot new material, since dedicated TV cameras were big and bulky.

When the popularity of network television prompted a huge drop in cinema ticket sales, the film industry needed ways to differentiate their offerings. Its first tactic was the move to ‘widescreen’ film formats, presenting an impressive landscape image that TV sets couldn’t compete with.

Up ‘Scope

Early widescreen systems used multiple projectors and non-standard film formats, which were expensive and impractical. However, this all changed with the introduction of CinemaScope in 1953.

CinemaScope uses an anamorphic lens to compress the image onto 35mm film stock, resulting in a distorted image that’s tall and thin. A single projector then decompresses the image, stretching it horizontally and presenting a wide, panoramic image. The standard 1:33 frame produced an image with an aspect ratio of up to 2.66:1, which was later reduced to 2.35:1 to accommodate an optical soundtrack.

CinemaScope films could still be viewed on a TV, but the conversion clipped a 1.33:1 section of the widescreen film, losing imagery on either side. Between the grand vistas experienced in theatres, and the egregious ‘pan and scan’ TV cropping, it was generally recognised that widescreen movies were best viewed at the cinema, and the film industry was back in business.

Aspect ratio
Cinemascope film frame with stereo soundtrack and “squeezed” image
Same image, as projected

CinemaScope and its derivatives dominated Hollywood for the next 50 years. A variety of different aspect ratios were used – including 1.66:1, which found favour in Europe and Asia – but by the end of the 20th Century, 1.85:1 was the most common format used by film studios.

One ratio to rule them all

The adoption of 1.85:1 as the aspect ratio of choice for movies is no surprise when you realise that it’s very close to the 16:9 (or 1.77:1) ratio that has been defined for widescreen televisions. The 16:9 ratio was chosen by SMPTE in the early 1980s because it was close to an average between the major widescreen cinema formats of the time.

Since 2000, however – and perhaps as a response to TVs increasing dominance – there has been a shift in moviemaking, from the standard 1.85:1 to a wider 2.35:1 or 2.39:1 aspect ratio. The wider frame is now by far the more dominant format, especially among the top-grossing blockbuster movies.

Dozens of different aspect ratios have been used over the years, but the majority of digital video content is still consumed at 16:9 and 4:3, although the latter is increasingly rare. TVs, smartphones and computer monitors are mostly formatted for 16:9 viewing, albeit with a few exceptions. These include ultrawide monitors and Sony Xperia smartphones, which have 21:9 screens (2.33:1) that can show widescreen movies in their full glory.

Imagen provides an award-winning platform for cost-effectively distributing large volumes of video content through a range of business models. To find out more about how Imagen’s media management and distribution solution can unlock the full potential of your video, talk to us.

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