How were TV size ratios defined and why did we go from 4:3 to 16:9?
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4:3 was agreed upon many, many years ago. At some point movies decided to go to widescreen to differentiate themselves from TV and thus offer some added value. Much more recently TVs also went widescreen, but it’s worth noting TVs use _different_ widescreen ratios than many movies.
IIRC, 4×3 mimic old playhouses, so that was what was adopted in early TV. As movie theaters gained popularity in the 70’s and 80’s, the presentation was widened to 16×9. Then came HD TV standards in the late 1990’s and things where standardized. Sort of.
Also, one of the reasons in case of LCD screens is that with the same diagonal 16:9 matrix has smaller pixel area and is therefore cheaper to produce.
Movies turned to around 2.35:1. In order to display both 4×3 and 2.35:1 without or with minimal “pan&scan” (zooming in to fill the screen and panning the zoom window depending on the shot), they decided on 16×9. Since 4×3 is naturally 12×9, that means it an easily be displayed with pillar-boxes (black bars on the sides); 2.35:1 is close enough to 16×7 that it can be displayed with minimal cropping with letter-boxes (black bars on top/bottom) or can go through pan&scan without much loss of information to the sides of the frame.
4×3 = ~1.33:1
16×9 = ~1.78:1
One reason that wide screens became more prevalent was the ubiquitousness of LCD technology. In the days of CRTs, the electron beam had to be bent by a magnet to illuminate different parts of the screen. The further from the center, the more the beam had to be bent. This either caused a loss of image quality, created issues with hitting the pixel “masks/grids”, or required to tv to be physically larger (deeper). A widescreen tv would have to be just as large as a screen with the same width but more height, so it didn’t make sense for the screens to be wide. With LCDs, you can make a screen with pretty much any aspect ratio you want, and we prefer wide screens.
The first TVs had screens with a 4:3 aspect ratio, which was the most suitable aspect ratio for the cathode ray tubes that were used to display images on the screen. Cathode ray tubes (CRTs) are vacuum tubes that produce images by directing a beam of electrons at a phosphorescent screen, creating a pattern of light and darkness that corresponds to the image being displayed. CRTs were the primary technology used for TVs until the mid-2000s, when they were replaced by flat-panel displays such as LCDs and LEDs.
The 4:3 aspect ratio was also used for early movies, which were shot on film with a frame size of 35mm. The frame size of 35mm film is roughly equivalent to a 4:3 aspect ratio, which is why early TVs used this aspect ratio. As movie-making technology improved and widescreen movies became more popular, the 16:9 aspect ratio became the standard for TVs, as it is more suitable for displaying widescreen content.
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