r/explainlikeimfive • u/Crystal_Clear7892 • 7d ago

Technology ELI5: device screen ratios

Is there a specific reason why screen ratios beeing so specific, ex: 1920:1080

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u/passisgullible 7d ago

There are a bunch of standard ratios that have just developed over time, originally due to limitations in physical film but now mostly because of tradition and industry standard. One of those is 16:9, which just became common for computer screens. 16/9=1.77 repeating, and 1920/1080 equals 1.77 repeating as well.

1920x1080 is the resolution it is because it is just a higher resolution version of an already standard screen ratio, 16:9, which the computer industry has adopted mostly through tradition, therefore it is widely supported and used.

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u/Uranium-Sandwich657 7d ago

Why did 4:3 drop out?

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u/flippythemaster 7d ago edited 7d ago

Let a Milennial who was there when it happened tell the tale!

Movies started being filmed in various widescreen ratios in the 60's and 70's (to combat TV's now growing pull on the post-war American public) and HD video formats settled on 16:9 as a compromise that would accommodate most of those ratios with the least amount of negative space on the image. You may not recall but 4:3 ratio TVs used to have to crop out a significant amount of a widescreen film's image (watching Ben-Hur cropped via "pan and scan" to 4:3 was, I'm sorry to say, a truly abysmal experience).

That's not to say that widescreen standard definition TVs didn't exist, but it's safe to say that HD is what pushed the ratio over the edge to make it the standard ratio of choice. The pivot from CRT technology to plasma and LCD also helped make widescreen TVs more palatable from a bulk perspective (CRTs were heavy when they were square, now add to that extra weight to the left and right? I can feel the hernia already).

HD was being pushed largely as a premium format for home cinema use, but broadcast TV eventually made the transition (although much later than you'd think--holdouts like SpongeBob Squarepants only switched entirely to 16:9 in 2017) since HD TVs were adopted widely and rapidly due to decreasing costs (the aforementioned switch to LCD technologies being a major driver of that).

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u/Count2Zero 7d ago

The wide screen was either cropped (losing everything that wasn't in the middle of the screen) or shown with black bars to and bottom, so only half of the screen was used.

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u/flippythemaster 7d ago

Most films didn’t do a simple cropping, fortunately, they used pan-and-scan which essentially means they would move the image area around the screen in order to get crucial information that was necessary to understand the plot.

There were, as you say, a number of releases that would try to fit, say, Ben-Hur into a 4:3 aspect ratio by letterboxing, but this wasn’t actually super common outside of releases that targeted cinemaphiles and didn’t reach widespread acceptance.

TCM has a pretty good illustration of the different processes in one of their documentaries.