The reason this didn’t happen is that the number didn’t match the size of the resolution increase. Display and broadcast resolutions have always referred to resolution in terms of horizontal lines, with the letters “i” and “p” referring to interlacing, which skips every other line, and progressive scan, which doesn’t: 576i (PAL), 480i (NTSC), 576p (DVD), 720p, 1080i, 1080p, and so on.
The real solution would have been to abandon the 4K moniker entirely and instead use the designation 2160p. (Read: 8K UHDTV: How do you send a 48Gbps TV signal over terrestrial airwaves?) It’s reasonable to refer to these two UHD variants as 4K UHD and 8K UHD - but, to be more precise, the 8K UHD spec should probably be renamed QUHD (Quad Ultra HD). There’s 3,840 by 2,160, and then there’s a big step up, to 7,680 by 4,320, which is also called UHD. To make matters more confusing, UHD is actually split in two. But the vast majority are 3,840 by 2,160, for a 1.78:1 aspect ratio. Sure, there are some panels out there that are 4,096 by 2,160, which adds up to an aspect ratio of 1.9:1. It’s not the same as the 4K resolution made above - and yet almost every TV or monitor you see advertised as 4K is actually UHD. UHD quadruples that resolution to 3,840 by 2,160. Ultra High Definition, or UHD for short, is the next step up from what’s called full HD, the official name for the display resolution of 1,920 by 1,080.
(See: How digital technology is reinventing cinema.) A DCI 4K stream is compressed using JPEG2000, can have a bitrate of up to 250Mbps, and employs 12-bit 4:4:4 color depth. The 4K standard is not just a resolution, either: It also defines how 4K content is encoded. 4K refers to the fact that the horizontal pixel count (4,096) is roughly four thousand. In this case, 4K is 4,096 by 2,160 and is exactly four times the previous standard for digital editing and projection (2K, or 2,048 by 1,080).
The term “4K” originally derives from the Digital Cinema Initiatives (DCI), a consortium of motion picture studios that standardized a spec for the production and digital projection of 4K content.
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