Why is 2160p video called 4K?
In: 4205
Others have explained part of this, but part of it has to do with context and history.
1280x720p is the original “HD” resolution, while 1920x1080p is “full HD”. 1080p ended up becoming very popular in television, while other resolutions faded.
Because of how scaling works, it is best to quadruple resolution rather than increase it in smaller increments – it means that older content will look normal on a higher resolution screen.
So the next step up was 3840×2160 (4k) which is exactly 4x the resolution of 1080p.
So the reason that “4K” has less than 4,000 horizontal pixels (3840×2160) is because it was quadruple that of the previous popular TV resolution – 1920×1080.
Computer monitors had a similar change, where 720 was popular, and then 2560×1440 became popular.
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